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                                                              [EXHIBIT 12(a)(3)]

                         NOTICE OF GUARANTEED DELIVERY

                                      for

                        TENDER OF SHARES OF COMMON STOCK

                                       of

                             SPECTRA-PHYSICS, INC.

    As set forth in the section captioned "The Tender Offer--Procedures For
Accepting The Offer And Tendering Shares" in the Offer to Purchase described
below, this Notice of Guaranteed Delivery or one substantially in the form
hereof must be used to tender shares of common stock, par value $0.01 per share
(the "Shares"), of Spectra-Physics, Inc., a Delaware corporation (the
"Company"), pursuant to the Offer (as defined below) if certificates evidencing
Shares are not immediately available or the certificates evidencing Shares and
all other required documents cannot be delivered to EquiServe Trust
Company, N.A. (the "Depositary") prior to the Expiration Date (as defined in the
Offer to Purchase), or if the procedures for delivery by book-entry transfer
cannot be completed on a timely basis. This instrument may be delivered by hand
or transmitted by facsimile transmission, overnight courier or mail to the
Depositary.

                        THE DEPOSITARY FOR THE OFFER IS:

                         EQUISERVE TRUST COMPANY, N.A.

<Table>
                                    
              BY MAIL:                         BY OVERNIGHT COURIER:
           EquiServe Trust                        EquiServe Trust
          Corporate Actions                   Attn: Corporate Actions
        Post Office Box 43025                   40 Campanelli Drive
      Providence, RI 02940-3025                 Braintree, MA 02184
</Table>

                                    BY HAND:
                        Securities Transfer & Reporting
                              c/o EquiServe Trust
                         100 William's Street, Galleria
                            New York, New York 10038

  FACSIMILE NUMBER 781-575-4826 AND FACSIMILE CONFIRMATION NUMBER 781-575-4816

    DELIVERY OF THIS NOTICE OF GUARANTEED DELIVERY TO AN ADDRESS OTHER THAN AS
SET FORTH ABOVE, OR TRANSMISSIONS OF INSTRUCTIONS VIA A FACSIMILE NUMBER OTHER
THAN AS SET FORTH ABOVE, WILL NOT CONSTITUTE A VALID DELIVERY.

    THIS NOTICE OF GUARANTEED DELIVERY IS NOT TO BE USED TO GUARANTEE
SIGNATURES. IF A SIGNATURE ON A LETTER OF TRANSMITTAL IS REQUIRED TO BE
GUARANTEED BY AN ELIGIBLE INSTITUTION (AS DEFINED IN THE OFFER TO PURCHASE)
UNDER THE INSTRUCTIONS THERETO, SUCH SIGNATURE GUARANTEE MUST APPEAR IN THE
APPLICABLE SPACE PROVIDED IN THE SIGNATURE BOX IN THE LETTER OF TRANSMITTAL.

              THE GUARANTEE ON THE REVERSE SIDE MUST BE COMPLETED.
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Ladies and Gentlemen:

    The undersigned hereby tenders to Spectra-Physics Acquisition, Inc., a
Delaware corporation and a wholly-owned subsidiary of Thermo Electron
Corporation, a Delaware corporation, upon the terms and subject to the
conditions set forth in the Offer to Purchase dated November 16, 2001 (the
"Offer to Purchase") and in the related Letter of Transmittal (which, together
with any amendments or supplements thereto, collectively constitute the
"Offer"), receipt of each of which is hereby acknowledged, the number of Shares
indicated below pursuant to the guaranteed delivery procedures set forth in the
section of the Offer to Purchase captioned "The Tender Offer--Procedures For
Accepting The Offer And Tendering Shares."

Signature(s): __________________________________________________________________

Name(s) of Record Holder(s): ___________________________________________________

________________________________________________________________________________

________________________________________________________________________________
                              Please Type or Print

Number of Shares: ______________________________________________________________

Share Certificate No(s).(if available): ________________________________________

________________________________________________________________________________

________________________________________________________________________________

Dated: ___________________________________________________________________, 2001

Address: _______________________________________________________________________

________________________________________________________________________________
                                                                        Zip Code

Area Code and Tel. No.(s): _____________________________________________________

Check box if Shares will be tendered by book-entry transfer: / /

DTC Account Number: ____________________________________________________________
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                                   GUARANTEE
                   (NOT TO BE USED FOR SIGNATURE GUARANTEES)

    The undersigned, a firm which is a commercial bank, broker, dealer, credit
union, savings association or other entity which is a member in good standing of
the Securities Transfer Agents Medallion Program, the Stock Exchanges' Medallion
Program or the New York Stock Exchange, Inc. Medallion Signature Program, hereby
guarantees to either deliver to the Depositary certificates evidencing all the
Shares tendered hereby, in proper form for transfer, or to deliver such Shares
pursuant to the procedure for book-entry transfer into the Depositary's account
at The Depository Trust Company, in either case together with the Letter of
Transmittal, properly completed and duly executed, with any required signature
guarantees or an Agent's Message (as defined in the Offer to Purchase) in the
case of a book-entry transfer, and any other required documents, all within
three Nasdaq trading days after the date hereof.
- --------------------------------------------------------------------------------

Name of Firm: __________________________________________________________________

Address: _______________________________________________________________________

 _______________________________________________________________________________
                                                                        Zip Code

Area Code and Tel. No.: ________________________________________________________

Authorized Signature: __________________________________________________________

Name: __________________________________________________________________________

Title: _________________________________________________________________________

Dated: __________________, 2001
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      NOTE: DO NOT SEND CERTIFICATES WITH THIS NOTICE OF GUARANTEED DELIVERY.
          CERTIFICATES SHOULD BE SENT WITH YOUR LETTER OF TRANSMITTAL.