As filed with the Securities and Exchange Commission on November 24, 1998.
                                     Registration No.333-

                       SECURITIES AND EXCHANGE COMMISSION

                             WASHINGTON, D.C. 20549
                                 ---------------

                                    FORM S-8
                             Registration Statement
                                      Under
                           The Securities Act of 1933
                                 ---------------

                            THERMO OPTEK CORPORATION
             (Exact name of registrant as specified in its charter)
                                 ---------------

      DELAWARE                                                   04-3283973
(State or other jurisdiction of                             (I.R.S. Employer
 incorporation or organization)                        Identification Number)

                              8 East Forge Parkway
                          Franklin, Massachusetts 02038
               (Address of Principal Executive Offices) (Zip Code)


                 THERMO OPTEK CORPORATION EQUITY INCENTIVE PLAN

        THERMO OPTEK CORPORATION DEFERRED COMPENSATION PLAN FOR DIRECTORS

    THERMO ELECTRON CORPORATION - THERMO OPTEK CORPORATION NONQUALIFIED STOCK
                                   OPTION PLAN

  THERMO INSTRUMENT SYSTEMS INC. - THERMO OPTEK CORPORATION NONQUALIFIED STOCK
                                   OPTION PLAN

                THERMO ELECTRON CORPORATION MONEYMATCH PLUS PLAN

             THERMO OPTEK CORPORATION EMPLOYEES' STOCK PURCHASE PLAN

             THERMO ELECTRON CORPORATION DIRECTORS STOCK OPTION PLAN

           THERMO INSTRUMENT SYSTEMS INC. DIRECTORS STOCK OPTION PLAN


                           (Full Titles of the Plans)


<PAGE>



                          Sandra L. Lambert, Secretary
                            Thermo Optek Corporation
                         c/o Thermo Electron Corporation
                                 81 Wyman Street
                                 P. O. Box 9046
                        Waltham, Massachusetts 02454-9046
                     (Name and Address of Agent for Service)

                                  (781) 622-1000
          (Telephone Number, Including Area Code, of Agent For Service)

                                   Copies to:
                    Seth H. Hoogasian, Esq., General Counsel
                            Thermo Optek Corporation
                         c/o Thermo Electron Corporation
                                 81 Wyman Street
                                 P. O. Box 9046
                        Waltham, Massachusetts 02454-9046

                                 ---------------

                         CALCULATION OF REGISTRATION FEE


  Title of                                   Proposed Maximum
 securities         Amount       Proposed       Aggregate         Amount of
   to be            to be        Maximum      Offering Price     Registration 
registered        registered     Offering                             Fee
                                 Price Per
                                   Share
  Common Stock,
 $.01 par value     2,062,500     $9.5625(3)    $19,722,656.25        $5,483
    per share         shares                         (3)
                      (1)(2)


      In  addition,  pursuant to Rule 416(c) under the  Securities  Act of 1933,
this Registration  Statement also covers an indeterminate amount of interests to
be offered or sold pursuant to the employee  benefit plans described  herein and
an  indeterminate  number of shares of the  Registrant's  Common Stock as may be
issuable  in  connection  with  adjustments  under the  employee  benefit  plans
described  herein  to  reflect  certain  changes  in  the  Registrant's  capital
structure, including stock dividends or stock splits.

(1)   The shares registered hereunder are divided among the various plans as set
      forth in the following table:

      Name of Plan                                               No. of Shares

      Thermo Optek Corporation
            Employees Equity Incentive Plan                           450,000

<PAGE>


      Thermo Electron Corporation - Thermo Optek Corporation
            Nonqualified Stock Option Plan                            375,000

      Thermo Instrument Systems Inc. - Thermo Optek
            Corporation Nonqualified Stock
            Option Plan                                               750,000

      Thermo Electron Corporation MoneyMatch Plus Plan                200,000

      Thermo Optek Corporation Employees'
            Stock Purchase Plan                                       100,000

      Thermo Electron Corporation Directors
            Stock Option Plan                                         150,000

      Thermo Instrument Systems Inc. Directors
            Stock Option Plan                                          37,500


(2)   The number of shares of Common  Stock which will  actually be issued under
      the Thermo  Electron  Corporation  MoneyMatch  Plus Plan (the  "MoneyMatch
      Plan")  cannot be  determined  at this  time,  as the  number of shares of
      Common Stock  purchased by the  administrator  of the MoneyMatch Plan will
      depend on the amount of contributions to be used to purchase shares of the
      Registrant's  Common  Stock in the open market and the  prevailing  market
      prices.

(3)   Estimated  solely  for  the  purpose  of  calculating  the  amount  of the
      registration  fee in accordance  with Rule 457(h) under the Securities Act
      of 1933. The calculation of the proposed maximum aggregate  offering price
      has been based upon (1) the  registration  hereunder  of an  aggregate  of
      2,062,500  shares and (2) the  average  of the high and low sales  prices,
      $9.625 and $9.50,  respectively,  of the Registrant's  Common Stock on the
      American   Stock  Exchange  on  November  20,  1998  as  reported  in  the
      consolidated reporting system.



<PAGE>



                                      
                                     PART I

              INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

      The information  required by Part I is included in documents sent or given
to the  respective  participants  in the plans  listed on the cover page of this
Registration  Statement  pursuant to Rule 428(b)(1)  under the Securities Act of
1933, as amended (the "Securities Act"). As used in this Registration Statement,
the terms "Registrant" or "Company" refer to Thermo Optek Corporation.


                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3.  Incorporation of Documents by Reference.

      The Registrant is subject to the informational and reporting  requirements
of Sections 13(a),  13(c), 14 and 15(d) of the Securities  Exchange Act of 1934,
as amended (the  "Exchange  Act"),  and in accordance  therewith  files reports,
proxy  statements  and  other  information  with  the  Securities  and  Exchange
Commission (the "Commission").  The following documents,  which are on file with
the Commission, are incorporated in this Registration Statement by reference:

            (a)   The  Company's  Annual Report on Form 10-K for the fiscal year
                  ended January 3, 1998.

            (b)   The  Company's  Quarterly  Report on Form 10-Q for the  fiscal
                  quarter ended April 4, 1998.

            (c)   The  Company's  Quarterly  Report on Form 10-Q for the  fiscal
                  quarter ended July 4, 1998.

            (d)   The  Company's  Current  Report  on Form  8-K  filed  with the
                  Commission on September 29, 1998.

            (e)   The  Company's  Quarterly  Report on Form 10-Q for the  fiscal
                  quarter ended October 3, 1998.

            (f)   The  description of the Common Stock which is contained in the
                  Company's  Registration  Statement on Form 8-A filed under the
                  Exchange Act, as such  description may be amended from time to
                  time.

      All reports or proxy  statements filed by the Company pursuant to Sections
13(a),  13(c),  14 and 15(d) of the Exchange Act  subsequent to the date of this
Registration  Statement  and prior to the filing of a  post-effective  amendment
that  indicates  that all  securities  offered  herein  have been sold,  or that
deregisters  all such securities  then remaining  unsold,  shall be deemed to be
incorporated by reference in this Registration Statement and to be a part hereof
from the respective dates of filing of such documents.
<PAGE>

Item 4.  Description of Securities.

      Not applicable.

Item 5.  Interests of Named Experts and Counsel.

      The  validity of the Common Stock  offered  hereby has been passed upon by
Seth H.  Hoogasian,  Esq.,  General Counsel of the Company.  Mr.  Hoogasian is a
full-time  employee of Thermo  Electron  Corporation  ("Thermo  Electron"),  the
majority  stockholder of Thermo Instrument  Systems Inc. ("Thermo  Instrument"),
which in turn is the majority  stockholder of the Company,  is an officer of the
Company,  Thermo  Instrument and Thermo  Electron,  and owns or has the right to
acquire  6,000 shares of Common Stock,  20,973 shares of the common stock,  $.10
par value per  share,  of Thermo  Instrument  and  123,028  shares of the common
stock, $1.00 par value per share, of Thermo Electron.

Item 6.  Indemnification of Directors and Officers.

      The Delaware  General  Corporation  Law and the Company's  Certificate  of
Incorporation  and By-Laws  limit the  monetary  liability  of  directors to the
Company and to its stockholders and provide for indemnification of the Company's
officers and directors for  liabilities and expenses that they may incur in such
capacities.  In general,  officers and directors are indemnified with respect to
actions  taken in good faith in a manner  reasonably  believed  to be in, or not
opposed to, the best  interests of the Company and, with respect to any criminal
action or proceeding,  actions that the  indemnitee  had no reasonable  cause to
believe were unlawful. The Company also has indemnification  agreements with its
directors and officers that provide for the maximum  indemnification  allowed by
law.

      Thermo  Electron has an insurance  policy which  insures the directors and
officers of Thermo Electron and its subsidiaries, including the Company, against
certain  liabilities  which might be incurred in connection with the performance
of their duties.

Item 7.  Exemption from Registration Claimed.

      Not Applicable.

Item 8.  Exhibits.

      The Exhibit Index  immediately  preceding the exhibits is attached  hereto
and incorporated herein by reference.

Item 9.  Undertakings.

      (a)   The undersigned Registrant hereby undertakes:

            (1) To file,  during any  period in which  offers or sales are being
made, a post-effective amendment to this registration statement:
<PAGE>

                  (i)    To include any prospectus required by Section 10(a)(3)
                           of the Securities Act of 1933;

                  (ii) To reflect in the  prospectus any facts or events arising
      after the effective date of the registration statement (or the most recent
      post-effective amendment thereof) which, individually or in the aggregate,
      represent  a  fundamental  change  in the  information  set  forth  in the
      registration  statement.  Notwithstanding  the foregoing,  any increase or
      decrease in volume of  securities  offered (if the total  dollar  value of
      securities  offered  would not exceed that which was  registered)  and any
      deviation from the low or high end of the estimated maximum offering range
      may be  reflected  in the form of  prospectus  filed  with the  Commission
      pursuant  to Rule 424(b) if, in the  aggregate,  the changes in volume and
      price  represent no more than 20 percent  change in the maximum  aggregate
      offering price set forth in the "Calculation of Registration Fee" table in
      the effective registration statement;

                  (iii) To include any material  information with respect to the
      plan  of  distribution  not  previously   disclosed  in  the  registration
      statement or any material change to such  information in the  registration
      statement.

      Provided,  however,  that paragraphs (a)(1)(i) and (a)(1)(ii) do not apply
if the  information  required to be included in a  post-effective  amendment  by
those paragraphs is contained in periodic reports filed with or furnished to the
Commission  by the  Registrant  pursuant  to Section 13 or Section  15(d) of the
Securities  Exchange  Act of 1934  that are  incorporated  by  reference  in the
registration statement.

            (2) That,  for the purpose of  determining  any liability  under the
Securities Act of 1933, each such post-effective amendment shall be deemed to be
a new registration statement relating to the securities offered therein, and the
offering of such  securities at that time shall be deemed to be the initial bona
fide offering thereof.

            (3)  To  remove  from  registration  by  means  of a  post-effective
amendment  any of the  securities  being  registered  which remain unsold at the
termination of the offering.

      (b) The undersigned  Registrant  hereby  undertakes  that, for purposes of
determining  any liability  under the Securities Act of 1933, each filing of the
Registrant's  annual report pursuant to Section 13(a) or 15(d) of the Securities
Exchange Act of 1934 (and, where applicable,  each filing of an employee benefit
plan's annual report pursuant to Section 15(d) of the Securities Exchange Act of
1934) that is incorporated by reference in the  registration  statement shall be
deemed to be a new  registration  statement  relating to the securities  offered
therein,  and the offering of such securities at that time shall be deemed to be
the initial bona fide offering thereof.
<PAGE>


      (c)  Insofar  as  indemnification   for  liabilities   arising  under  the
Securities Act of 1933 may be permitted to directors,  officers and  controlling
persons of the Registrant  pursuant to the foregoing  provisions,  or otherwise,
the  Registrant  has been  advised  that in the  opinion of the  Securities  and
Exchange  Commission such  indemnification is against public policy as expressed
in the Act and is,  therefore,  unenforceable.  In the  event  that a claim  for
indemnification  against  such  liabilities  (other  than  the  payment  by  the
Registrant of expenses  incurred or paid by a director,  officer or  controlling
person of the  Registrant  in the  successful  defense  of any  action,  suit or
proceeding)  is  asserted by such  director,  officer or  controlling  person in
connection with the securities being registered,  the Registrant will, unless in
the opinion of its counsel the matter has been settled by controlling precedent,
submit  to a  court  of  appropriate  jurisdiction  the  question  whether  such
indemnification  by it is against public policy as expressed in the Act and will
be governed by the final adjudication of such issue.


<PAGE>


                                   SIGNATURES

      Pursuant to the requirements of the Securities Act of 1933, the Registrant
certifies  that it has  reasonable  grounds to believe  that it meets all of the
requirements  for  filing  on Form S-8 and has  duly  caused  this  Registration
Statement  to be  signed  on its  behalf  by  the  undersigned,  thereunto  duly
authorized, in the City of Franklin, Commonwealth of Massachusetts, on this 24th
day of November, 1998.

                                        THERMO OPTEK CORPORATION


                                    By: /s/  Robert J. Rosenthal
                                             Robert J. Rosenthal
                                             President and
                                             Chief Executive Officer


                                POWER OF ATTORNEY

      Each of the undersigned Directors and Officers of Thermo Optek Corporation
hereby appoints John N. Hatsopoulos, Paul F. Kelleher, Kenneth J. Apicerno, Seth
H.  Hoogasian  and  Sandra L.  Lambert,  and each of them,  his true and  lawful
attorneys-in-fact  and agents,  with full power of substitution,  for him and in
his  name,  place  and  stead,  in any and all  capacities,  to sign any and all
amendments (including post-effective amendments) to this Registration Statement,
and to file the same, with all exhibits thereto, and all documents in connection
therewith,  with the  Securities  and Exchange  Commission,  granting  unto said
attorneys-in-fact  and agents,  and each of them, full power and authority to do
and perform each and every act and thing  requisite  and necessary to be done in
and about the  premises,  as fully to all  intents  and  purposes as he might or
could  do  in  person,   hereby   ratifying   and   confirming   all  that  said
attorneys-in-fact  and  agents  or any of them,  or their or his  substitute  or
substitutes, may lawfully do or cause to be done by virtue thereof.

      Pursuant  to  the  requirements  of  the  Securities  Act  of  1933,  this
Registration  Statement  has been signed below by the  following  persons in the
capacities and on the dates indicated:

            
Signature                         Title                          Date

                              
/s/ Robert J. Rosenthal       President, Chief Executive    November 24, 1998
------------------------      Officer and Director
Robert J. Rosenthal
                                   
/s/ John N. Hatsopoulos       Chief Financial Officer and   November 24, 1998
------------------------      Senior Vice President
John N. Hatsopoulos
<PAGE>

/s/ Paul F. Kelleher          Chief Accounting Officer      November 24, 1998
------------------------
Paul F. Kelleher
                                         
/s/ Earl R. Lewis             Chairman of the Board of      November 24, 1998
------------------------      Directors 
Earl R. Lewis

/s/ George N. Hatsopoulos     Director                      November 24, 1998
-------------------------
George N. Hatsopoulos


s/ Stephen R. Levy            Director                      November 24, 1998
------------------------
Stephen R. Levy


/s/ Robert A. McCabe          Director                      November 24, 1998
------------------------
Robert A. McCabe




<PAGE>


      Pursuant to the  requirements  of the  Securities Act of 1933, as amended,
the Plan Administrator of the Thermo Electron  Corporation  MoneyMatch Plus Plan
has duly caused this  Registration  Statement  to be signed on its behalf by the
undersigned,  thereunto duly authorized, in the City of Waltham, Commonwealth of
Massachusetts, on this 24th day of November, 1998.

                              Thermo Electron Corporation
                              MoneyMatch Plus Plan

                              By:   Thermo Electron Corporation,
                                    Plan Administrator



                                    By:   /s/ Kenneth J. Apicerno
                                              Kenneth J. Apicerno
                                              Treasurer




<PAGE>


                                  EXHIBIT INDEX


Exhibit
Number            Description


5.1               Opinion of Seth H. Hoogasian, Esq.

5.2               Internal Revenue Service  Determination  Letter, dated May 15,
                  1995, with respect to the qualification of the Thermo Electron
                  Corporation MoneyMatch Plus Plan under Section 401 of the
                  Internal Revenue Code.

23.1              Consent of Arthur Andersen LLP

23.2              Consent of Seth H. Hoogasian, Esq.
                  (contained in his opinion filed as
                  Exhibit 5).

24                Power of Attorney (see  signature  pages to this  Registration
                  Statement).



<PAGE>





                                                                 EXHIBIT 5.1



                            Thermo Optek Corporation
                              8 East Forge Parkway
                          Franklin, Massachusetts 02038




                                                      November 24, 1998

Thermo Optek Corporation
8 East Forge Parkway
Franklin, Massachusetts 02038

Re:   Registration Statement on Form S-8
      Relating to 2,062,500 Shares of the Common Stock,
      $.01 par value, of Thermo Optek Corporation

Dear Sirs:

      I am General Counsel to Thermo Optek Corporation,  a Delaware  corporation
(the  "Company"),  and have acted as counsel in connection with the registration
under the  Securities  Act of 1933, as amended,  on Form S-8 (the  "Registration
Statement"),  of 2,062,500 shares of the Company's Common Stock,  $.01 par value
per share (the "Shares") subject to the following  employee benefit plans (each,
a "Plan"), as well as an indeterminate amount of related interests in such Plans
(the  "Interests"):  Thermo Optek  Corporation  Employees Equity Incentive Plan,
Thermo Electron Corporation - Thermo Optek Corporation Nonqualified Stock Option
Plan,  Thermo Instrument  Systems Inc. - Thermo Optek  Corporation  Nonqualified
Stock Option Plan,  Thermo Electron  Corporation  MoneyMatch  Plus Plan,  Thermo
Optek Corporation  Employees' Stock Purchase Plan,  Thermo Electron  Corporation
Directors Stock Option Plan, and Thermo Instrument Systems Inc.
Directors Stock Option Plan.

      I or a member of my legal staff have  reviewed the  corporate  proceedings
taken by the Company  with respect to the  authorization  of the issuance of the
Shares.  I or a member of my legal  staff have also  examined  and  relied  upon
originals or copies, certified or otherwise authenticated to my satisfaction, of
all corporate records, documents, agreements or other instruments of the Company
and have made all  investigations  of law and have  discussed with the Company's
representatives   all  questions  of  fact  that  I  have  deemed  necessary  or
appropriate.

<PAGE>

      Based upon and subject to the foregoing, I am of the opinion that:

      1. The Company is a corporation  duly organized,  validly  existing and in
corporate good standing under the laws of the State of Delaware.

      2. The issuance and sale of the Shares as contemplated in the Registration
Statement have been duly authorized by the Company.

      3. The Shares,  when issued and sold in accordance  with the provisions of
the applicable Plan, will be validly issued, fully paid and nonassessable.

      I am also of the opinion that the respective  Plans confer valid Interests
upon the  participants  in such  Plans,  to the  extent  and upon the  terms and
conditions described in such Plans.

      I hereby  consent  to the filing of this  opinion  as  Exhibit  5.1 to the
Registration Statement.

                                          Very truly yours,




                                          Seth H. Hoogasian
                                          General Counsel


<PAGE>


                                                                 EXHIBIT 5.2



Internal Revenue Service                Department of the Treasury
District Director
G.P.O. Box 1680
Brooklyn, NY 11202

                                        Employer Identification Number:
Date:  May 15, 1995                               04-2209186
                                        File Folder Number:
                                             043002050
THERMO ELECTRON CORPORATION             Person to Contact:
81 WYMAN STREET                         SANDRA JORDAN
WALTHAM, MA 02254                       Contact Telephone Number:
                                             (617) 565-7808
                                        Plan Name:
                                        THERMO ELECTRON CORPORATION
                                        MONEY MATCH PLUS PLAN
                                        Plan Number: 001

Dear Applicant:

      We have made a favorable  determination  on your plan,  identified  above,
based on the  information  supplied.  Please keep this letter in your  permanent
records.

      Continued  qualification of the plan under its present form will depend on
its  effect  in  operation.   (See  section  1.401-1(b)(3)  of  the  Income  Tax
Regulations.) We will review the status of the plan in operation periodically.

      The  enclosed   document  explains  the  significance  of  this  favorable
determination  letter,  points out some  features  that may affect the qualified
status  of your  employee  retirement  plan,  and  provides  information  on the
reporting  requirements  for your  plan.  It also  describes  some  events  that
automatically nullify it. It is very important that you read the publication.

      This  letter  relates  only to the status of your plan under the  Internal
Revenue Code. It is not a determination regarding the effect of other federal or
local statutes.

      This determination is subject to your adoption of the proposed  amendments
submitted in your letter dated December 30, 1994. The proposed amendments should
be  adopted  on or before  the date  prescribed  by the  regulations  under Code
section 401 (b).

      This plan has been mandatorily disaggregated,  permissively aggregated, or
restructured to satisfy the nondiscrimination requirements.

     This letter is issued under Rev.  Proc.  93-39 and considers the amendments
required by the Tax Reform Act of 1986  except as  otherwise  specified  in this
letter.
<PAGE>

      This   plan   satisfies   the   nondiscriminatory   current   availability
requirements  of section 1.401  (a)(4)-4(b) of the  regulations  with respect to
those  benefits,  rights,  and  features  that are  currently  available  to all
employees in the plan's  coverage group.  For this purpose,  the plan's coverage
group consists of those employees  treated as currently  benefiting for purposes
of demonstrating  that the plan satisfies the minimum  coverage  requirements of
section 410(b) of the Code.

      This   plan   satisfies   the   nondiscriminatory   current   availability
requirements  of section 1.401  (a)(4)-4(b) of the  regulations  with respect to
those  benefits,  rights,  and  features  that are  currently  available  to all
employees in the plan's  coverage group.  For this purpose,  the plan's coverage
group consists of those employees  treated as currently  benefiting for purposes
of demonstrating  that the plan satisfies the minimum  coverage  requirements of
section 410 (b) of the Code.

      This plan also satisfies the requirements of section  1.401(a)(4)-4(b)  of
the regulations with respect to the specific  benefits,  rights, or features for
which you have provided information.

     This  letter  may not be  relied  upon with  respect  to  whether  the plan
satisfies  the  qualification  requirements  as  amended  by the  Uruguay  Round
Agreements Act, Pub. L. 103-465.

      The  information  on the  enclosed  addendum is an  integral  part of this
determination. Please be sure to read and keep it with this letter.

      We have sent a copy of this letter to your  representative as indicated in
the power of attorney.

      If you have questions  concerning  this matter,  please contact the person
whose name and telephone number are shown above.

                                             Sincerely yours,


                                             /s/ Herbert J. Huff
                                             Herbert J. Huff
                                             District Director

Enclosures:
Publication 794
Reporting & Disclosure Guide
  for Employee Benefit Plans
Addendum



<PAGE>


                                                                 Exhibit 23.1


                        [ARTHUR ANDERSEN LLP LETTERHEAD]



            Consent of Independent Public Accountants
            -----------------------------------------


     As independent public  accountants,  we hereby consent to the incorporation
by  reference  in this  registration  statement  on Form S-8 of our report dated
February 17, 1998, included in Thermo Optek Corporation's  Annual Report on Form
10-K for the year  ended  January  3, 1998,  and to all  references  to our Firm
included in this registration statement.


                                                Arthur Andersen LLP



Boston, Massachusetts
November 24, 1998
[{"type": "S-8", "sequence": "1", "description": "FORM S-8", "secsgml_size_bytes": 28890}]
{"company-data": {"conformed-name": "THERMO OPTEK CORP", "cik": "0001012368", "assigned-sic": "3826", "irs-number": "043283973", "state-of-incorporation": "DE", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-67869", "film-number": "98758685"}, "business-address": {"street1": "8E FORGE PARKWAY", "street2": "P.O. BOX 9046", "city": "FRANKLIN", "state": "MA", "zip": "02038", "phone": "6176221000"}, "mail-address": {"street1": "81 WALTHAM STREET", "street2": "P.O. BOX 9046", "city": "WALTHAM", "state": "MA", "zip": "02154"}}
As filed with the Securities and Exchange Commission on November 24, 1998.
                                     Registration No.333-

                       SECURITIES AND EXCHANGE COMMISSION

                             WASHINGTON, D.C. 20549
                                 ---------------

                                    FORM S-8
                             Registration Statement
                                      Under
                           The Securities Act of 1933
                                 ---------------

                            THERMO OPTEK CORPORATION
             (Exact name of registrant as specified in its charter)
                                 ---------------

      DELAWARE                                                   04-3283973
(State or other jurisdiction of                             (I.R.S. Employer
 incorporation or organization)                        Identification Number)

                              8 East Forge Parkway
                          Franklin, Massachusetts 02038
               (Address of Principal Executive Offices) (Zip Code)

                 THERMO OPTEK CORPORATION EQUITY INCENTIVE PLAN

        THERMO OPTEK CORPORATION DEFERRED COMPENSATION PLAN FOR DIRECTORS

    THERMO ELECTRON CORPORATION - THERMO OPTEK CORPORATION NONQUALIFIED STOCK
                                   OPTION PLAN

  THERMO INSTRUMENT SYSTEMS INC. - THERMO OPTEK CORPORATION NONQUALIFIED STOCK
                                   OPTION PLAN

                THERMO ELECTRON CORPORATION MONEYMATCH PLUS PLAN

             THERMO OPTEK CORPORATION EMPLOYEES' STOCK PURCHASE PLAN

             THERMO ELECTRON CORPORATION DIRECTORS STOCK OPTION PLAN

           THERMO INSTRUMENT SYSTEMS INC. DIRECTORS STOCK OPTION PLAN

                           (Full Titles of the Plans)
Sandra L. Lambert, Secretary
                            Thermo Optek Corporation
                         c/o Thermo Electron Corporation
                                 81 Wyman Street
                                 P. O. Box 9046
                        Waltham, Massachusetts 02454-9046
                     (Name and Address of Agent for Service)

                                  (781) 622-1000
          (Telephone Number, Including Area Code, of Agent For Service)

                                   Copies to:
                    Seth H. Hoogasian, Esq., General Counsel
                            Thermo Optek Corporation
                         c/o Thermo Electron Corporation
                                 81 Wyman Street
                                 P. O. Box 9046
                        Waltham, Massachusetts 02454-9046

                                 ---------------

                         CALCULATION OF REGISTRATION FEE

  Title of                                   Proposed Maximum
 securities         Amount       Proposed       Aggregate         Amount of
   to be            to be        Maximum      Offering Price     Registration 
registered        registered     Offering                             Fee
                                 Price Per
                                   Share
  Common Stock,
 $.01 par value     2,062,500     $9.5625(3)    $19,722,656.25        $5,483
    per share         shares                         (3)
                      (1)(2)

      In  addition,  pursuant to Rule 416(c) under the  Securities  Act of 1933,
this Registration  Statement also covers an indeterminate amount of interests to
be offered or sold pursuant to the employee  benefit plans described  herein and
an  indeterminate  number of shares of the  Registrant's  Common Stock as may be
issuable  in  connection  with  adjustments  under the  employee  benefit  plans
described  herein  to  reflect  certain  changes  in  the  Registrant's  capital
structure, including stock dividends or stock splits.

(1)   The shares registered hereunder are divided among the various plans as set
      forth in the following table:

      Name of Plan                                               No. of Shares

      Thermo Optek Corporation
            Employees Equity Incentive Plan                           450,000
Thermo Electron Corporation - Thermo Optek Corporation
            Nonqualified Stock Option Plan                            375,000

      Thermo Instrument Systems Inc. - Thermo Optek
            Corporation Nonqualified Stock
            Option Plan                                               750,000

      Thermo Electron Corporation MoneyMatch Plus Plan                200,000

      Thermo Optek Corporation Employees'
            Stock Purchase Plan                                       100,000

      Thermo Electron Corporation Directors
            Stock Option Plan                                         150,000

      Thermo Instrument Systems Inc. Directors
            Stock Option Plan                                          37,500

(2)   The number of shares of Common  Stock which will  actually be issued under
      the Thermo  Electron  Corporation  MoneyMatch  Plus Plan (the  "MoneyMatch
      Plan")  cannot be  determined  at this  time,  as the  number of shares of
      Common Stock  purchased by the  administrator  of the MoneyMatch Plan will
      depend on the amount of contributions to be used to purchase shares of the
      Registrant's  Common  Stock in the open market and the  prevailing  market
      prices.

(3)   Estimated  solely  for  the  purpose  of  calculating  the  amount  of the
      registration  fee in accordance  with Rule 457(h) under the Securities Act
      of 1933. The calculation of the proposed maximum aggregate  offering price
      has been based upon (1) the  registration  hereunder  of an  aggregate  of
      2,062,500  shares and (2) the  average  of the high and low sales  prices,
      $9.625 and $9.50,  respectively,  of the Registrant's  Common Stock on the
      American   Stock  Exchange  on  November  20,  1998  as  reported  in  the
      consolidated reporting system.
PART I

              INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

      The information  required by Part I is included in documents sent or given
to the  respective  participants  in the plans  listed on the cover page of this
Registration  Statement  pursuant to Rule 428(b)(1)  under the Securities Act of
1933, as amended (the "Securities Act"). As used in this Registration Statement,
the terms "Registrant" or "Company" refer to Thermo Optek Corporation.

                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3.  Incorporation of Documents by Reference.

      The Registrant is subject to the informational and reporting  requirements
of Sections 13(a),  13(c), 14 and 15(d) of the Securities  Exchange Act of 1934,
as amended (the  "Exchange  Act"),  and in accordance  therewith  files reports,
proxy  statements  and  other  information  with  the  Securities  and  Exchange
Commission (the "Commission").  The following documents,  which are on file with
the Commission, are incorporated in this Registration Statement by reference:

            (a)   The  Company's  Annual Report on Form 10-K for the fiscal year
                  ended January 3, 1998.

            (b)   The  Company's  Quarterly  Report on Form 10-Q for the  fiscal
                  quarter ended April 4, 1998.

            (c)   The  Company's  Quarterly  Report on Form 10-Q for the  fiscal
                  quarter ended July 4, 1998.

            (d)   The  Company's  Current  Report  on Form  8-K  filed  with the
                  Commission on September 29, 1998.

            (e)   The  Company's  Quarterly  Report on Form 10-Q for the  fiscal
                  quarter ended October 3, 1998.

            (f)   The  description of the Common Stock which is contained in the
                  Company's  Registration  Statement on Form 8-A filed under the
                  Exchange Act, as such  description may be amended from time to
                  time.

      All reports or proxy  statements filed by the Company pursuant to Sections
13(a),  13(c),  14 and 15(d) of the Exchange Act  subsequent to the date of this
Registration  Statement  and prior to the filing of a  post-effective  amendment
that  indicates  that all  securities  offered  herein  have been sold,  or that
deregisters  all such securities  then remaining  unsold,  shall be deemed to be
incorporated by reference in this Registration Statement and to be a part hereof
from the respective dates of filing of such documents.
Item 4.  Description of Securities.

      Not applicable.

Item 5.  Interests of Named Experts and Counsel.

      The  validity of the Common Stock  offered  hereby has been passed upon by
Seth H.  Hoogasian,  Esq.,  General Counsel of the Company.  Mr.  Hoogasian is a
full-time  employee of Thermo  Electron  Corporation  ("Thermo  Electron"),  the
majority  stockholder of Thermo Instrument  Systems Inc. ("Thermo  Instrument"),
which in turn is the majority  stockholder of the Company,  is an officer of the
Company,  Thermo  Instrument and Thermo  Electron,  and owns or has the right to
acquire  6,000 shares of Common Stock,  20,973 shares of the common stock,  $.10
par value per  share,  of Thermo  Instrument  and  123,028  shares of the common
stock, $1.00 par value per share, of Thermo Electron.

Item 6.  Indemnification of Directors and Officers.

      The Delaware  General  Corporation  Law and the Company's  Certificate  of
Incorporation  and By-Laws  limit the  monetary  liability  of  directors to the
Company and to its stockholders and provide for indemnification of the Company's
officers and directors for  liabilities and expenses that they may incur in such
capacities.  In general,  officers and directors are indemnified with respect to
actions  taken in good faith in a manner  reasonably  believed  to be in, or not
opposed to, the best  interests of the Company and, with respect to any criminal
action or proceeding,  actions that the  indemnitee  had no reasonable  cause to
believe were unlawful. The Company also has indemnification  agreements with its
directors and officers that provide for the maximum  indemnification  allowed by
law.

      Thermo  Electron has an insurance  policy which  insures the directors and
officers of Thermo Electron and its subsidiaries, including the Company, against
certain  liabilities  which might be incurred in connection with the performance
of their duties.

Item 7.  Exemption from Registration Claimed.

      Not Applicable.

Item 8.  Exhibits.

      The Exhibit Index  immediately  preceding the exhibits is attached  hereto
and incorporated herein by reference.

Item 9.  Undertakings.

      (a)   The undersigned Registrant hereby undertakes:

            (1) To file,  during any  period in which  offers or sales are being
made, a post-effective amendment to this registration statement:
(i)    To include any prospectus required by Section 10(a)(3)
                           of the Securities Act of 1933;

                  (ii) To reflect in the  prospectus any facts or events arising
      after the effective date of the registration statement (or the most recent
      post-effective amendment thereof) which, individually or in the aggregate,
      represent  a  fundamental  change  in the  information  set  forth  in the
      registration  statement.  Notwithstanding  the foregoing,  any increase or
      decrease in volume of  securities  offered (if the total  dollar  value of
      securities  offered  would not exceed that which was  registered)  and any
      deviation from the low or high end of the estimated maximum offering range
      may be  reflected  in the form of  prospectus  filed  with the  Commission
      pursuant  to Rule 424(b) if, in the  aggregate,  the changes in volume and
      price  represent no more than 20 percent  change in the maximum  aggregate
      offering price set forth in the "Calculation of Registration Fee" table in
      the effective registration statement;

                  (iii) To include any material  information with respect to the
      plan  of  distribution  not  previously   disclosed  in  the  registration
      statement or any material change to such  information in the  registration
      statement.

      Provided,  however,  that paragraphs (a)(1)(i) and (a)(1)(ii) do not apply
if the  information  required to be included in a  post-effective  amendment  by
those paragraphs is contained in periodic reports filed with or furnished to the
Commission  by the  Registrant  pursuant  to Section 13 or Section  15(d) of the
Securities  Exchange  Act of 1934  that are  incorporated  by  reference  in the
registration statement.

            (2) That,  for the purpose of  determining  any liability  under the
Securities Act of 1933, each such post-effective amendment shall be deemed to be
a new registration statement relating to the securities offered therein, and the
offering of such  securities at that time shall be deemed to be the initial bona
fide offering thereof.

            (3)  To  remove  from  registration  by  means  of a  post-effective
amendment  any of the  securities  being  registered  which remain unsold at the
termination of the offering.

      (b) The undersigned  Registrant  hereby  undertakes  that, for purposes of
determining  any liability  under the Securities Act of 1933, each filing of the
Registrant's  annual report pursuant to Section 13(a) or 15(d) of the Securities
Exchange Act of 1934 (and, where applicable,  each filing of an employee benefit
plan's annual report pursuant to Section 15(d) of the Securities Exchange Act of
1934) that is incorporated by reference in the  registration  statement shall be
deemed to be a new  registration  statement  relating to the securities  offered
therein,  and the offering of such securities at that time shall be deemed to be
the initial bona fide offering thereof.
(c)  Insofar  as  indemnification   for  liabilities   arising  under  the
Securities Act of 1933 may be permitted to directors,  officers and  controlling
persons of the Registrant  pursuant to the foregoing  provisions,  or otherwise,
the  Registrant  has been  advised  that in the  opinion of the  Securities  and
Exchange  Commission such  indemnification is against public policy as expressed
in the Act and is,  therefore,  unenforceable.  In the  event  that a claim  for
indemnification  against  such  liabilities  (other  than  the  payment  by  the
Registrant of expenses  incurred or paid by a director,  officer or  controlling
person of the  Registrant  in the  successful  defense  of any  action,  suit or
proceeding)  is  asserted by such  director,  officer or  controlling  person in
connection with the securities being registered,  the Registrant will, unless in
the opinion of its counsel the matter has been settled by controlling precedent,
submit  to a  court  of  appropriate  jurisdiction  the  question  whether  such
indemnification  by it is against public policy as expressed in the Act and will
be governed by the final adjudication of such issue.
SIGNATURES

      Pursuant to the requirements of the Securities Act of 1933, the Registrant
certifies  that it has  reasonable  grounds to believe  that it meets all of the
requirements  for  filing  on Form S-8 and has  duly  caused  this  Registration
Statement  to be  signed  on its  behalf  by  the  undersigned,  thereunto  duly
authorized, in the City of Franklin, Commonwealth of Massachusetts, on this 24th
day of November, 1998.

                                        THERMO OPTEK CORPORATION

                                    By: /s/  Robert J. Rosenthal
                                             Robert J. Rosenthal
                                             President and
                                             Chief Executive Officer

                                POWER OF ATTORNEY

      Each of the undersigned Directors and Officers of Thermo Optek Corporation
hereby appoints John N. Hatsopoulos, Paul F. Kelleher, Kenneth J. Apicerno, Seth
H.  Hoogasian  and  Sandra L.  Lambert,  and each of them,  his true and  lawful
attorneys-in-fact  and agents,  with full power of substitution,  for him and in
his  name,  place  and  stead,  in any and all  capacities,  to sign any and all
amendments (including post-effective amendments) to this Registration Statement,
and to file the same, with all exhibits thereto, and all documents in connection
therewith,  with the  Securities  and Exchange  Commission,  granting  unto said
attorneys-in-fact  and agents,  and each of them, full power and authority to do
and perform each and every act and thing  requisite  and necessary to be done in
and about the  premises,  as fully to all  intents  and  purposes as he might or
could  do  in  person,   hereby   ratifying   and   confirming   all  that  said
attorneys-in-fact  and  agents  or any of them,  or their or his  substitute  or
substitutes, may lawfully do or cause to be done by virtue thereof.

      Pursuant  to  the  requirements  of  the  Securities  Act  of  1933,  this
Registration  Statement  has been signed below by the  following  persons in the
capacities and on the dates indicated:

            
Signature                         Title                          Date

                              
/s/ Robert J. Rosenthal       President, Chief Executive    November 24, 1998
------------------------      Officer and Director
Robert J. Rosenthal
                                   
/s/ John N. Hatsopoulos       Chief Financial Officer and   November 24, 1998
------------------------      Senior Vice President
John N. Hatsopoulos
/s/ Paul F. Kelleher          Chief Accounting Officer      November 24, 1998
------------------------
Paul F. Kelleher
                                         
/s/ Earl R. Lewis             Chairman of the Board of      November 24, 1998
------------------------      Directors 
Earl R. Lewis

/s/ George N. Hatsopoulos     Director                      November 24, 1998
-------------------------
George N. Hatsopoulos

s/ Stephen R. Levy            Director                      November 24, 1998
------------------------
Stephen R. Levy

/s/ Robert A. McCabe          Director                      November 24, 1998
------------------------
Robert A. McCabe
Pursuant to the  requirements  of the  Securities Act of 1933, as amended,
the Plan Administrator of the Thermo Electron  Corporation  MoneyMatch Plus Plan
has duly caused this  Registration  Statement  to be signed on its behalf by the
undersigned,  thereunto duly authorized, in the City of Waltham, Commonwealth of
Massachusetts, on this 24th day of November, 1998.

                              Thermo Electron Corporation
                              MoneyMatch Plus Plan

                              By:   Thermo Electron Corporation,
                                    Plan Administrator

                                    By:   /s/ Kenneth J. Apicerno
                                              Kenneth J. Apicerno
                                              Treasurer
EXHIBIT INDEX

Exhibit
Number            Description

5.1               Opinion of Seth H. Hoogasian, Esq.

5.2               Internal Revenue Service  Determination  Letter, dated May 15,
                  1995, with respect to the qualification of the Thermo Electron
                  Corporation MoneyMatch Plus Plan under Section 401 of the
                  Internal Revenue Code.

23.1              Consent of Arthur Andersen LLP

23.2              Consent of Seth H. Hoogasian, Esq.
                  (contained in his opinion filed as
                  Exhibit 5).

24                Power of Attorney (see  signature  pages to this  Registration
                  Statement).
EXHIBIT 5.1

                            Thermo Optek Corporation
                              8 East Forge Parkway
                          Franklin, Massachusetts 02038

                                                      November 24, 1998

Thermo Optek Corporation
8 East Forge Parkway
Franklin, Massachusetts 02038

Re:   Registration Statement on Form S-8
      Relating to 2,062,500 Shares of the Common Stock,
      $.01 par value, of Thermo Optek Corporation

Dear Sirs:

      I am General Counsel to Thermo Optek Corporation,  a Delaware  corporation
(the  "Company"),  and have acted as counsel in connection with the registration
under the  Securities  Act of 1933, as amended,  on Form S-8 (the  "Registration
Statement"),  of 2,062,500 shares of the Company's Common Stock,  $.01 par value
per share (the "Shares") subject to the following  employee benefit plans (each,
a "Plan"), as well as an indeterminate amount of related interests in such Plans
(the  "Interests"):  Thermo Optek  Corporation  Employees Equity Incentive Plan,
Thermo Electron Corporation - Thermo Optek Corporation Nonqualified Stock Option
Plan,  Thermo Instrument  Systems Inc. - Thermo Optek  Corporation  Nonqualified
Stock Option Plan,  Thermo Electron  Corporation  MoneyMatch  Plus Plan,  Thermo
Optek Corporation  Employees' Stock Purchase Plan,  Thermo Electron  Corporation
Directors Stock Option Plan, and Thermo Instrument Systems Inc.
Directors Stock Option Plan.

      I or a member of my legal staff have  reviewed the  corporate  proceedings
taken by the Company  with respect to the  authorization  of the issuance of the
Shares.  I or a member of my legal  staff have also  examined  and  relied  upon
originals or copies, certified or otherwise authenticated to my satisfaction, of
all corporate records, documents, agreements or other instruments of the Company
and have made all  investigations  of law and have  discussed with the Company's
representatives   all  questions  of  fact  that  I  have  deemed  necessary  or
appropriate.
Based upon and subject to the foregoing, I am of the opinion that:

      1. The Company is a corporation  duly organized,  validly  existing and in
corporate good standing under the laws of the State of Delaware.

      2. The issuance and sale of the Shares as contemplated in the Registration
Statement have been duly authorized by the Company.

      3. The Shares,  when issued and sold in accordance  with the provisions of
the applicable Plan, will be validly issued, fully paid and nonassessable.

      I am also of the opinion that the respective  Plans confer valid Interests
upon the  participants  in such  Plans,  to the  extent  and upon the  terms and
conditions described in such Plans.

      I hereby  consent  to the filing of this  opinion  as  Exhibit  5.1 to the
Registration Statement.

                                          Very truly yours,

                                          Seth H. Hoogasian
                                          General Counsel
EXHIBIT 5.2

Internal Revenue Service                Department of the Treasury
District Director
G.P.O. Box 1680
Brooklyn, NY 11202

                                        Employer Identification Number:
Date:  May 15, 1995                               04-2209186
                                        File Folder Number:
                                             043002050
THERMO ELECTRON CORPORATION             Person to Contact:
81 WYMAN STREET                         SANDRA JORDAN
WALTHAM, MA 02254                       Contact Telephone Number:
                                             (617) 565-7808
                                        Plan Name:
                                        THERMO ELECTRON CORPORATION
                                        MONEY MATCH PLUS PLAN
                                        Plan Number: 001

Dear Applicant:

      We have made a favorable  determination  on your plan,  identified  above,
based on the  information  supplied.  Please keep this letter in your  permanent
records.

      Continued  qualification of the plan under its present form will depend on
its  effect  in  operation.   (See  section  1.401-1(b)(3)  of  the  Income  Tax
Regulations.) We will review the status of the plan in operation periodically.

      The  enclosed   document  explains  the  significance  of  this  favorable
determination  letter,  points out some  features  that may affect the qualified
status  of your  employee  retirement  plan,  and  provides  information  on the
reporting  requirements  for your  plan.  It also  describes  some  events  that
automatically nullify it. It is very important that you read the publication.

      This  letter  relates  only to the status of your plan under the  Internal
Revenue Code. It is not a determination regarding the effect of other federal or
local statutes.

      This determination is subject to your adoption of the proposed  amendments
submitted in your letter dated December 30, 1994. The proposed amendments should
be  adopted  on or before  the date  prescribed  by the  regulations  under Code
section 401 (b).

      This plan has been mandatorily disaggregated,  permissively aggregated, or
restructured to satisfy the nondiscrimination requirements.

     This letter is issued under Rev.  Proc.  93-39 and considers the amendments
required by the Tax Reform Act of 1986  except as  otherwise  specified  in this
letter.
This   plan   satisfies   the   nondiscriminatory   current   availability
requirements  of section 1.401  (a)(4)-4(b) of the  regulations  with respect to
those  benefits,  rights,  and  features  that are  currently  available  to all
employees in the plan's  coverage group.  For this purpose,  the plan's coverage
group consists of those employees  treated as currently  benefiting for purposes
of demonstrating  that the plan satisfies the minimum  coverage  requirements of
section 410(b) of the Code.

      This   plan   satisfies   the   nondiscriminatory   current   availability
requirements  of section 1.401  (a)(4)-4(b) of the  regulations  with respect to
those  benefits,  rights,  and  features  that are  currently  available  to all
employees in the plan's  coverage group.  For this purpose,  the plan's coverage
group consists of those employees  treated as currently  benefiting for purposes
of demonstrating  that the plan satisfies the minimum  coverage  requirements of
section 410 (b) of the Code.

      This plan also satisfies the requirements of section  1.401(a)(4)-4(b)  of
the regulations with respect to the specific  benefits,  rights, or features for
which you have provided information.

     This  letter  may not be  relied  upon with  respect  to  whether  the plan
satisfies  the  qualification  requirements  as  amended  by the  Uruguay  Round
Agreements Act, Pub. L. 103-465.

      The  information  on the  enclosed  addendum is an  integral  part of this
determination. Please be sure to read and keep it with this letter.

      We have sent a copy of this letter to your  representative as indicated in
the power of attorney.

      If you have questions  concerning  this matter,  please contact the person
whose name and telephone number are shown above.

                                             Sincerely yours,

                                             /s/ Herbert J. Huff
                                             Herbert J. Huff
                                             District Director

Enclosures:
Publication 794
Reporting & Disclosure Guide
  for Employee Benefit Plans
Addendum
Exhibit 23.1

                        [ARTHUR ANDERSEN LLP LETTERHEAD]

            Consent of Independent Public Accountants
            -----------------------------------------

     As independent public  accountants,  we hereby consent to the incorporation
by  reference  in this  registration  statement  on Form S-8 of our report dated
February 17, 1998, included in Thermo Optek Corporation's  Annual Report on Form
10-K for the year  ended  January  3, 1998,  and to all  references  to our Firm
included in this registration statement.

                                                Arthur Andersen LLP

Boston, Massachusetts
November 24, 1998