<PAGE>

                                                                    EXHIBIT 4.12

THIS WARRANT AND THE COMMON SHARES ISSUABLE UPON EXERCISE OF THIS WARRANT HAVE
NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED. THIS WARRANT
AND THE COMMON SHARES ISSUABLE UPON EXERCISE OF THIS WARRANT MAY NOT BE SOLD,
OFFERED FOR SALE, PLEDGED OR HYPOTHECATED IN THE ABSENCE OF AN EFFECTIVE
REGISTRATION STATEMENT AS TO THIS WARRANT UNDER SAID ACT OR AN OPINION OF
COUNSEL REASONABLY SATISFACTORY TO JMAR TECHNOLOGIES, INC. THAT SUCH
REGISTRATION IS NOT REQUIRED.

                           Right to Purchase 200,000 Shares of Common Stock of
                           JMAR Technologies, Inc. (subject to adjustment as
                           provided herein)

                          COMMON STOCK PURCHASE WARRANT

No. 2003-4                                         Issue Date: December 17, 2003

         JMAR TECHNOLGIES, INC., a corporation organized under the laws of the
State of Delaware (the "COMPANY"), hereby certifies that, for value received,
LAURUS MASTER FUND, LTD., or assigns (the "HOLDER"), is entitled, subject to the
terms set forth below, to purchase from the Company from and after the Issue
Date of this Warrant and at any time or from time to time before 5:00 p.m., New
York time, through seven (7) years after such date (the "EXPIRATION DATE"), up
to 200,000 fully paid and nonassessable shares of Common Stock (as hereinafter
defined), $.01 par value per share, of the Company, at the Exercise Price (as
defined below). The number and character of such shares of Common Stock and the
Exercise Price are subject to adjustment as provided herein.

         As used herein the following terms, unless the context otherwise
requires, have the following respective meanings:

         (a)      The term "Company" shall include JMAR Technologies, Inc. and
any corporation which shall succeed or assume the obligations of JMAR
Technologies, Inc. hereunder.

         (b)      The term "Common Stock" includes (a) the Company's Common
Stock, $.01 par value per share, and (b) any other securities into which or for
which any of the securities described in (a) may be converted or exchanged
pursuant to a plan of recapitalization, reorganization, merger, sale of assets
or otherwise.

         (c)      The term "Other Securities" refers to any stock (other than
Common Stock) and other securities of the Company or any other person (corporate
or otherwise) which the holder of the Warrant at any time shall be entitled to
receive, or shall have received, on the exercise of the Warrant, in lieu of or
in addition to Common Stock, or which at any time shall be issuable or shall
have been issued in exchange for or in replacement of Common Stock or Other
Securities pursuant to Section 4 or otherwise.

<PAGE>

         (d)      The term "EXERCISE PRICE" shall be $2.25 per share;

         1.       EXERCISE OF WARRANT.

                  1.1      Number of Shares Issuable upon Exercise. From and
after the date hereof through and including the Expiration Date, the Holder
shall be entitled to receive, upon exercise of this Warrant in whole or in part,
by delivery of an original or fax copy of the exercise notice attached hereto as
Exhibit A (the "EXERCISE NOTICE"), shares of Common Stock of the Company,
subject to adjustment pursuant to Section 4.

                  1.2      Fair Market Value. Fair Market Value of a share of
Common Stock as of a particular date (the "DETERMINATION DATE") shall mean:

                           (a)      If the Company's Common Stock is traded on
an exchange or is quoted on the National Association of Securities Dealers, Inc.
Automated Quotation ("NASDAQ") National Market or the NASDAQ SmallCap Market,
then the closing or last sale price, respectively, reported for the last
business day immediately preceding the Determination Date.

                           (b)      If the Company's Common Stock is not traded
on an exchange or on the NASDAQ National Market or the NASDAQ SmallCap Market
but is traded on the NASD OTC Bulletin Board or BBX Exchange, then the mean of
the average of the closing bid and asked prices reported for the last business
day immediately preceding the Determination Date.

                           (c)      Except as provided in clause (d) below, if
the Company's Common Stock is not publicly traded, then as the Holder and the
Company agree or in the absence of agreement by arbitration in accordance with
the rules then in effect of the American Arbitration Association, before a
single arbitrator to be chosen from a panel of persons qualified by education
and training to pass on the matter to be decided.

                           (d)      If the Determination Date is the date of a
liquidation, dissolution or winding up, or any event deemed to be a liquidation,
dissolution or winding up pursuant to the Company's charter, then all amounts to
be payable per share to holders of the Common Stock pursuant to the charter in
the event of such liquidation, dissolution or winding up, plus all other amounts
to be payable per share in respect of the Common Stock in liquidation under the
charter, assuming for the purposes of this clause (d) that all of the shares of
Common Stock then issuable upon exercise of the Warrant are outstanding at the
Determination Date.

         2.       PROCEDURE FOR EXERCISE.

                  2.1      Delivery of Stock Certificates, etc. on Exercise. The
Company agrees that the shares of Common Stock purchased upon exercise of this
Warrant shall be deemed to be issued to the Holder as the record owner of such
shares as of the close of business on the date on which this Warrant shall have
been surrendered and payment made for such shares as aforesaid. As soon as
practicable after the exercise of this Warrant in full or in part, and in any
event within 3 business days thereafter, the Company at its expense (including
the payment by it of any applicable issue taxes) will cause to be issued in the
name of and delivered to the Holder, or as

                                       2

<PAGE>

such Holder (upon payment by such holder of any applicable transfer taxes) may
direct in compliance with applicable securities laws, a certificate or
certificates for the number of duly and validly issued, fully paid and
nonassessable shares of Common Stock (or Other Securities) to which such Holder
shall be entitled on such exercise, plus, in lieu of any fractional share to
which such holder would otherwise be entitled, cash equal to such fraction
multiplied by the then Fair Market Value of one full share, together with any
other stock or other securities and property (including cash, where applicable)
to which such Holder is entitled upon such exercise pursuant to Section 1 or
otherwise.

                  2.2      Exercise.

                           (a)      Payment may be made by delivery of the
Warrant, and/or Common Stock receivable upon exercise of the Warrant in
accordance with Section (b) below, for the number of Common Shares specified in
such form (as such exercise number shall be adjusted to reflect any adjustment
in the total number of shares of Common Stock issuable to the holder per the
terms of this Warrant) and the Holder shall thereupon be entitled to receive the
number of duly authorized, validly issued, fully-paid and non-assessable shares
of Common Stock (or Other Securities) determined as provided herein.

                           (b)      Notwithstanding any provisions herein to the
contrary, if the Fair Market Value of one share of Common Stock is greater than
the Exercise Price (at the date of calculation as set forth below), the Holder
may elect to receive shares equal to the value (as determined below) of this
Warrant (or the portion thereof being exercised) by surrender of this Warrant at
the principal office of the Company together with the properly endorsed Exercise
Notice in which event the Company shall issue to the Holder a number of shares
of Common Stock computed using the following formula:

                  X=Y (A-B)
                      -----
                        A
                  -------

            Where X=       the number of shares of Common Stock to be issued to
                           the Holder

                  Y=       the number of shares of Common Stock purchasable
                           under the Warrant or, if only a portion of the
                           Warrant is being exercised, the portion of the
                           Warrant being exercised (at the date of such
                           calculation)

                  A=       the Fair Market Value of one share of the Company's
                           Common Stock (at the date of such calculation)

                  B=       Exercise Price (as adjusted to the date of such
                           calculation)

                                       3

<PAGE>

         3.       EFFECT OF REORGANIZATION, ETC.; ADJUSTMENT OF EXERCISE PRICE.

                  3.1      Reorganization, Consolidation, Merger, etc. In case
at any time or from time to time, the Company shall (a) effect a reorganization,
(b) consolidate with or merge into any other person, or (c) transfer all or
substantially all of its properties or assets to any other person under any plan
or arrangement contemplating the dissolution of the Company, then, in each such
case, as a condition to the consummation of such a transaction, proper and
adequate provision shall be made by the Company whereby the Holder of this
Warrant, on the exercise hereof as provided in Section 1 at any time after the
consummation of such reorganization, consolidation or merger or the effective
date of such dissolution, as the case may be, shall receive, in lieu of the
Common Stock (or Other Securities) issuable on such exercise prior to such
consummation or such effective date, the stock and other securities and property
(including cash) to which such Holder would have been entitled upon such
consummation or in connection with such dissolution, as the case may be, if such
Holder had so exercised this Warrant, immediately prior thereto, all subject to
further adjustment thereafter as provided in Section 4.

                  3.2      Dissolution. In the event of any dissolution of the
Company following the transfer of all or substantially all of its properties or
assets, the Company, prior to such dissolution, shall at its expense deliver or
cause to be delivered the stock and other securities and property (including
cash, where applicable) receivable by the Holder of the Warrant after the
effective date of such dissolution pursuant to Section 3.1 to a bank or trust
company having its principal office in New York, NY, as trustee for the Holder
of the Warrant.

                  3.3      Continuation of Terms. Upon any reorganization,
consolidation, merger or transfer (and any dissolution following any transfer)
referred to in this Section 3, this Warrant shall continue in full force and
effect and the terms hereof shall be applicable to the shares of stock and other
securities and property receivable on the exercise of this Warrant after the
consummation of such reorganization, consolidation or merger or the effective
date of dissolution following any such transfer, as the case may be, and shall
be binding upon the issuer of any such stock or other securities, including, in
the case of any such transfer, the person acquiring all or substantially all of
the properties or assets of the Company, whether or not such person shall have
expressly assumed the terms of this Warrant as provided in Section 4. In the
event this Warrant does not continue in full force and effect after the
consummation of the transactions described in this Section 3, then only in such
event will the Company's securities and property (including cash, where
applicable) receivable by the holders of the Warrant be delivered to the Trustee
as contemplated by Section 3.2.

                  3.4      Adjustment of Warrant Exercise Price and Number of
Shares upon Issuance of Common Stock. Other than (i) pursuant to warrants or
options that are outstanding as of the date hereof and warrants and options that
may be granted in the future under any option plan of the Company, or any
employment agreement, joint venture, credit, leasing or other financing
agreement or any joint venture or other strategic arrangement, in each case now
or hereinafter entered into by the Company, (ii) pursuant to any securities
issued by the Company to the Holder, (iii) pursuant to any agreement entered
into by the Company or any of its subsidiaries for the acquisition of another
business (whether by stock purchase or asset purchase, merger or otherwise;
((i), (ii) and (iii) above, are hereinafter referred to as the "EXCLUDED
ISSUANCES")), if the Company at any time shall issue any shares of Common Stock
prior to the complete exercise

                                       4

<PAGE>

of this Warrant for a consideration less than the Exercise Price that would be
in effect at the time of such issue, then, and thereafter successively upon each
such issue, the Exercise Price shall be reduced as follows: (i) the number of
shares of Common Stock outstanding immediately prior to such issue shall be
multiplied by the Exercise Price in effect at the time of such issue and the
product shall be added to the aggregate consideration, if any, received by the
Company upon such issue of additional shares of Common Stock; and (ii) the sum
so obtained shall be divided by the number of shares of Common Stock outstanding
immediately after such issue. The resulting quotient shall be the adjusted
Exercise Price. For purposes of this adjustment, the issuance of any security of
the Company carrying the right to convert such security into shares of Common
Stock or of any warrant, right or option to purchase Common Stock shall result
in an adjustment to the Exercise Price upon the issuance of shares of Common
Stock upon exercise of such conversion or purchase rights..

         4.       EXTRAORDINARY EVENTS REGARDING COMMON STOCK. In the event that
the Company shall (a) issue additional shares of the Common Stock as a dividend
or other distribution on outstanding Common Stock, (b) subdivide its outstanding
shares of Common Stock, or (c) combine its outstanding shares of the Common
Stock into a smaller number of shares of the Common Stock, then, in each such
event, the Exercise Price shall, simultaneously with the happening of such
event, be adjusted by multiplying the then Exercise Price by a fraction, the
numerator of which shall be the number of shares of Common Stock outstanding
immediately prior to such event and the denominator of which shall be the number
of shares of Common Stock outstanding immediately after such event, and the
product so obtained shall thereafter be the Exercise Price then in effect. The
Exercise Price, as so adjusted, shall be readjusted in the same manner upon the
happening of any successive event or events described herein in this Section 4.
The number of shares of Common Stock that the holder of this Warrant shall
thereafter, on the exercise hereof as provided in Section 1, be entitled to
receive shall be increased to a number determined by multiplying the number of
shares of Common Stock that would otherwise (but for the provisions of this
Section 4) be issuable on such exercise by a fraction of which (a) the numerator
is the Exercise Price that would otherwise (but for the provisions of this
Section 4) be in effect, and (b) the denominator is the Exercise Price in effect
on the date of such exercise.

         5.       CERTIFICATE AS TO ADJUSTMENTS. In each case of any adjustment
or readjustment in the shares of Common Stock (or Other Securities) issuable on
the exercise of the Warrant, the Company at its expense will promptly cause its
Chief Financial Officer or other appropriate designee to compute such adjustment
or readjustment in accordance with the terms of the Warrant and prepare a
certificate setting forth such adjustment or readjustment and showing in detail
the facts upon which such adjustment or readjustment is based, including a
statement of (a) the consideration received or receivable by the Company for any
additional shares of Common Stock (or Other Securities) issued or sold or deemed
to have been issued or sold, (b) the number of shares of Common Stock (or Other
Securities) outstanding or deemed to be outstanding, and (c) the Exercise Price
and the number of shares of Common Stock to be received upon exercise of this
Warrant, in effect immediately prior to such adjustment or readjustment and as
adjusted or readjusted as provided in this Warrant. The Company will forthwith
mail a copy of each such certificate to the holder of the Warrant and any
Warrant agent of the Company (appointed pursuant to Section 11 hereof).

                                       5

<PAGE>

         6.       RESERVATION OF STOCK, ETC. ISSUABLE ON EXERCISE OF WARRANT.
The Company will at all times reserve and keep available, solely for issuance
and delivery on the exercise of the Warrant, shares of Common Stock (or Other
Securities) from time to time issuable on the exercise of the Warrant.

         7.       ASSIGNMENT; EXCHANGE OF WARRANT. Subject to compliance with
applicable securities laws, this Warrant, and the rights evidenced hereby, may
be transferred by any registered holder hereof (a "TRANSFEROR") with respect to
any or all of the Shares. On the surrender for exchange of this Warrant, with
the Transferor's endorsement in the form of Exhibit B attached hereto (the
"TRANSFEROR ENDORSEMENT FORM") and together with evidence reasonably
satisfactory to the Company demonstrating compliance with applicable securities
laws, which shall include, without limitation, a legal opinion from the
Transferor's counsel that such transfer is exempt from the registration
requirements of applicable securities laws, the Company at its expense (but with
payment by the Transferor of any applicable transfer taxes) will issue and
deliver to or on the order of the Transferor thereof a new Warrant of like
tenor, in the name of the Transferor and/or the transferee(s) specified in such
Transferor Endorsement Form (each a "Transferee"), calling in the aggregate on
the face or faces thereof for the number of shares of Common Stock called for on
the face or faces of the Warrant so surrendered by the Transferor.

         8.       REPLACEMENT OF WARRANT. On receipt of evidence reasonably
satisfactory to the Company of the loss, theft, destruction or mutilation of
this Warrant and, in the case of any such loss, theft or destruction of this
Warrant, on delivery of an indemnity agreement or security reasonably
satisfactory in form and amount to the Company or, in the case of any such
mutilation, on surrender and cancellation of this Warrant, the Company at its
expense will execute and deliver, in lieu thereof, a new Warrant of like tenor.

         9.       REGISTRATION RIGHTS. The Holder of this Warrant has been
granted certain registration rights by the Company. These registration rights
are set forth in a Registration Rights Agreement entered into by the Company and
Purchaser at or prior to the issue date of this Warrant.

         10.      MAXIMUM EXERCISE. The Holder shall not be entitled to exercise
this Warrant on an exercise date, in connection with that number of shares of
Common Stock which would result in beneficial ownership by the Holder and its
affiliates of more than 4.99% of the shares of Common Stock of the Company on
such date. For the purposes of the proviso to the immediately preceding
sentence, beneficial ownership shall be determined in accordance with Section
13(d) of the Securities Exchange Act of 1934, as amended, and Regulation 13d-3
thereunder. Subject to the foregoing, the Holder shall not be limited to
aggregate exercises which would result in the issuance of more than 4.99%. The
restriction described in this paragraph may be revoked upon 75 days prior notice
from the Holder to the Company and is automatically null and void upon an Event
of Default under the Preferred Stock.

         11.      WARRANT AGENT. The Company may, by written notice to the each
holder of the Warrant, appoint an agent for the purpose of issuing Common Stock
(or Other Securities) on the exercise of this Warrant pursuant to Section 1,
exchanging this Warrant pursuant to Section 7, and replacing this Warrant
pursuant to Section 8, or any of the foregoing, and thereafter any such

                                       6

<PAGE>

issuance, exchange or replacement, as the case may be, shall be made at such
office by such agent.

         12.      TRANSFER ON THE COMPANY'S BOOKS. Until this Warrant is
transferred on the books of the Company, the Company may treat the registered
holder hereof as the absolute owner hereof for all purposes, notwithstanding any
notice to the contrary.

         13.      NOTICES, ETC. All notices and other communications from the
Company to the Holder of this Warrant shall be mailed by first class registered
or certified mail, postage prepaid, at such address as may have been furnished
to the Company in writing by such holder or, until any such Holder furnishes to
the Company an address, then to, and at the address of, the last Holder of this
Warrant who has so furnished an address to the Company.

         14.      MISCELLANEOUS. This Warrant and any term hereof may be
changed, waived, discharged or terminated only by an instrument in writing
signed by the party against which enforcement of such change, waiver, discharge
or termination is sought. This Warrant shall be governed by and construed in
accordance with the laws of State of New York without regard to principles of
conflicts of laws. Any action brought concerning the transactions contemplated
by this Warrant shall be brought only in the state courts of New York or in the
federal courts located in the state of New York; provided, however, that the
Holder may choose to waive this provision and bring an action outside the state
of New York. The individuals executing this Warrant on behalf of the Company
agree to submit to the jurisdiction of such courts and waive trial by jury. The
prevailing party shall be entitled to recover from the other party its
reasonable attorney's fees and costs. In the event that any provision of this
Warrant is invalid or unenforceable under any applicable statute or rule of law,
then such provision shall be deemed inoperative to the extent that it may
conflict therewith and shall be deemed modified to conform with such statute or
rule of law. Any such provision which may prove invalid or unenforceable under
any law shall not affect the validity or enforceability of any other provision
of this Warrant. The headings in this Warrant are for purposes of reference
only, and shall not limit or otherwise affect any of the terms hereof. The
invalidity or unenforceability of any provision hereof shall in no way affect
the validity or enforceability of any other provision. The Company acknowledges
that legal counsel participated in the preparation of this Warrant and,
therefore, stipulates that the rule of construction that ambiguities are to be
resolved against the drafting party shall not be applied in the interpretation
of this Warrant to favor any party against the other party.

                      [THIS SPACE INTENTIONALLY LEFT BLANK]

                                       7

<PAGE>

         IN WITNESS WHEREOF, the Company has executed this Warrant under seal as
of the date first written above.

                                             JMAR TECHNOLOGIES, INC.

                                             By: /s/ JOSEPH G. MARTINEZ

                                                 Joseph G. Martinez, Senior V.P.

Witness:

/s/ DENNIS E. VALENTINE

                                       8

<PAGE>

                                                                       EXHIBIT A

                              FORM OF SUBSCRIPTION
                   (To be signed only on exercise of Warrant)

TO:      JMAR Technologies, Inc.

The undersigned, pursuant to the provisions set forth in the attached Warrant
(No.____), hereby irrevocably elects to purchase (check applicable box):

___      ________ shares of the Common Stock covered by such Warrant; or

___ the maximum number of shares of Common Stock covered by such Warrant
pursuant to the cashless exercise procedure set forth in Section 2.

The undersigned herewith makes payment of the full Exercise Price for such
shares at the price per share provided for in such Warrant, which is
$___________. Such payment takes the form of (check applicable box or boxes):

___ the cancellation of such portion of the attached Warrant as is exercisable
for a total of _______ shares of Common Stock (using a Fair Market Value of
$_______ per share for purposes of this calculation); and/or

___ the cancellation of such number of shares of Common Stock as is necessary,
in accordance with the formula set forth in Section 2, to exercise this Warrant
with respect to the maximum number of shares of Common Stock purchaseable
pursuant to the cashless exercise procedure set forth in Section 2.

The undersigned requests that the certificates for such shares be issued in the
name of, and delivered to ____________________ whose address is ________________

_________________________________________.

The undersigned represents and warrants that all offers and sales by the
undersigned of the securities issuable upon exercise of the within Warrant shall
be made pursuant to registration of the Common Stock under the Securities Act of
1933, as amended (the "Securities Act") or pursuant to an exemption from
registration under the Securities Act.

Dated:___________________               ________________________________________
                                        (Signature must conform to name of
                                        holder as specified on the face of the
                                        Warrant)

                                        ________________________________________
                                        (Address)

<PAGE>

                                                                       EXHIBIT B

                         FORM OF TRANSFEROR ENDORSEMENT
                   (To be signed only on transfer of Warrant)

                  For value received, the undersigned hereby sells, assigns, and
transfers unto the person(s) named below under the heading "Transferees" the
right represented by the within Warrant to purchase the percentage and number of
shares of Common Stock of JMAR Technologies, Inc. to which the within Warrant
relates specified under the headings "Percentage Transferred" and "Number
Transferred," respectively, opposite the name(s) of such person(s) and appoints
each such person Attorney to transfer its respective right on the books of JMAR
Technologies, Inc. with full power of substitution in the premises.

<TABLE>
<CAPTION>
                        Percentage               Number
Transferees             Transferred           Transferrred
----------------------------------------------------------
<S>                     <C>                   <C>

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

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

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

----------------------------------------------------------
</TABLE>

Dated:___________________                   ____________________________________
                                            (Signature must conform to name of
                                            holder as specified on the face of
                                            the Warrant)

Signed in the presence of:

________________________________            ____________________________________
           (Name)                                       (address)

ACCEPTED AND AGREED:                        ____________________________________
[TRANSFEREE]                                             (address)

_______________________
         (Name)