<PAGE>

                                                                    EXHIBIT 10.4



THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED UNDER
THE SECURITIES ACT OF 1933, AS AMENDED, OR APPLICABLE STATE SECURITIES LAWS, AND
MAY NOT BE TRANSFERRED, SOLD OR OTHERWISE DISPOSED OF WITHOUT AN EFFECTIVE
REGISTRATION STATEMENT UNDER SUCH ACT AND REGISTRATION OR QUALIFICATION UNDER
APPLICABLE STATE SECURITIES LAWS OR PURSUANT TO AN EXEMPTION FROM THE
REGISTRATION REQUIREMENTS OF SUCH ACT AND APPLICABLE STATE SECURITIES LAWS,
SUPPORTED BY AN OPINION OF COUNSEL, REASONABLY SATISFACTORY TO THE COMPANY AND
ITS COUNSEL, THAT SUCH REGISTRATION IS NOT REQUIRED.



                              WARRANT CERTIFICATE

No. 00-9                                              Right to Purchase 184,000
                                                      Shares of Common Stock
                                                      (Subject to adjustment)

                WARRANT CERTIFICATE FOR PURCHASE OF COMMON STOCK

                           PHOTOELECTRON CORPORATION

                              This Certifies That

     FOR VALUE RECEIVED, KSH INVESTMENT GROUP, INC. or registered assigns (the
"Registered Holder") is the owner of the number of Common Stock Purchase
Warrants ("Warrants") specified above. Each Warrant initially entitles the
Registered Holder to purchase, subject to the terms and conditions set forth in
this Certificate and the Warrant Agreement (as hereinafter defined), one fully
paid and non-assessable share of Common Stock, $.01 par value ("Common Stock"),
of PHOTOELECTRON CORPORATION, a Massachusetts corporation (the "Company"), at
any time between the Initial Exercise Date (as herein defined) and the
Expiration Date (as hereinafter defined), upon the presentation and surrender of
this Warrant Certificate with the Subscription Form attached hereto duly
executed, at the corporate office of the Company, accompanied by payment of
$4.00 per share of common stock, subject to adjustment from time to time
pursuant to the terms and provisions of Section 8 of the Warrant Agreement in
lawful money of the United States of America in cash or by official bank or
certified check made payable to the Company.

     This Warrant Certificate and each Warrant represented hereby are issued
pursuant to and are subject in all respects to the terms and conditions set
forth in the Warrant Agreement (the "Warrant Agreement") made as of the 30th day
of June, 2000 by and between the Company and

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the Registered Holder. Terms not defined herein shall have the meanings assigned
to them in the Warrant Agreement.


     In the event of certain contingencies provided for in the Warrant
Agreement, the Exercise Price and/or the number of shares of Common Stock
subject to purchase upon the exercise of each Warrant represented hereby are
subject to modifications or adjustment.

     Each Warrant represented hereby is exercisable at the option of the
Registered Holder, but no fractional shares of Common Stock will be issued. In
the case of the exercise of less than all the Warrants represented hereby, the
Company shall cancel this Warrant Certificate upon the surrender hereof and
shall execute and deliver a new Warrant Certificate or Warrant Certificates of
like tenor, which the Warrant Agent shall countersign, for the balance of such
Warrants.

     The term "Initial Exercise Date" shall mean as of the date hereof.

     The term "Expiration Date" shall mean 5:00 p.m. (Eastern Standard time) on
June 30, 2005.  If such date shall in The Commonwealth of Massachusetts be a
holiday or a day on which banks are authorized or required to close, then the
Expiration Date shall mean 5:00 p.m. (Eastern Standard time) the next following
day which in The Commonwealth of Massachusetts is not a holiday or a day on
which banks are authorized or required to close.

     This Warrant Certificate shall be governed by and construed in accordance
with the laws of The Commonwealth of Massachusetts, without reference to
principles of conflicts of laws.

     IN WITNESS WHEREOF, the Company has caused this Warrant Certificate to be
duly executed, manually or in facsimile by its officer thereunto duly
authorized.

                                PHOTOELECTRON CORPORATION

                                By: /s/ Euan S. Thomson
                                   -------------------------------------
                                  Euan S. Thomson
                                  President and Chief Executive Officer

Date:  June 30, 2000

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                               SUBSCRIPTION FORM

    (To Be Executed by the Registered Holder in Order to Exercise Warrants)

                           __________________________

     Date:______________________


          The Undersigned hereby elects irrevocably to exercise the within
     Warrant and to purchase ____________ Shares of Common Stock of
     Photoelectron Corporation and hereby makes payment of
     $_____________________ (at the rate of $______________ per share) in
     payment of the Exercise Price pursuant thereto.  Please issue the shares as
     to which this Warrant is exercised in accordance with the instructions
     given below.

                                       OR

          The Undersigned hereby elects irrevocably to exercise the within
     Purchase Option and to purchase ___________ Shares of Common Stock of
     Photoelectron Corporation  by surrender of the unexercised portion of the
     within Warrant.  Please issue the Common Stock comprising the Warrant in
     accordance with the instructions given below.


                                           ______________________________
                                           Signature


                                           ______________________________
                                           Signature Guaranteed


                  INSTRUCTIONS FOR REGISTRATION OF SECURITIES

Name_________________________________________________________________________

                            (Print in Block Letters)

Address_______________________________________________________________________


     NOTICE:  The signature to this form must correspond with the name as
written upon the face of the within Warrant in every particular without
alteration or enlargement or any change whatsoever, and must be guaranteed by a
bank, other than a savings bank, or by a trust company or by a firm having
membership on a registered national securities exchange.

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                                   ASSIGNMENT

     (To Be Executed by the Registered Holder in Order to Assign Warrants)

                          ___________________________
     FOR VALUE RECEIVED, the Undersigned Registered Holder hereby sells, assigns
     and transfers unto

                   __________________________________________
                                 (insert name)

whose taxpayer identification or other identifying number is:
____________________ and whose address is:

                   __________________________________________

                   __________________________________________

                   __________________________________________

                   __________________________________________
                         (please print or type address)

the following number of the Warrants represented by this Warrant Certificate:
___________________, and hereby irrevocably constitutes and appoints
___________________ Attorney to transfer this Warrant Certificate on the books
of the Company, with full power of substitution in the premises.

                          ___________________________
                                     (Date)

                          ___________________________
                                  (Signature)


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