<PAGE>   1
[COMERICA LOGO]

                                                                    EXHIBIT 10.1

                             MASTER REVOLVING NOTE

              Variable Rate - Maturity Date - Obligatory Advances
                      (Business and Commercial Loans Only)

<TABLE>
<CAPTION>
--------------------------------------------------------------------------------
AMOUNT              NOTE DATE           MATURITY DATE         TAX IDENTIFICATION
--------------------------------------------------------------------------------
<S>                 <C>                 <C>                        <C>
$5,000,000.00       June 25, 1998       June 01, 1999              68-0131180
--------------------------------------------------------------------------------
</TABLE>

On the Maturity Date, as stated above, for value received, the undersigned
promise(s) to pay to the order of Comerica Bank-California ("Bank"), at any
office of the Bank in the State of California, Five Million and no/100 Dollars
(U.S.) or that portion of it advanced by the Bank and not repaid as later
provided) with interest until maturity, whether by acceleration or otherwise, or
an Event of Default, as later defined, at a per annum rate equal to the Bank's
base rate from time to time in effect plus  *0.000% per annum and after that
at a rate equal to the rate of interest otherwise prevailing under this Note
plus 3% per annum (but in no event in excess of the maximum rate permitted by
law). The Bank's "base rate" is that annual rate of interest so designated by
the Bank and which is changed by the Bank from time to time. Interest rate
changes will be effective for interest computation purposes as and when the
Bank's base rate changes. Interest shall be calculated on the basis of a
360-day year for the actual number of days the principal is outstanding.
Accrued interest on this Note shall be payable on the 1st day of each MONTH
commencing August 01, 1998, until the Maturity Date when all amounts
outstanding under this Note shall be due and payable in full. If the frequency
of interest payments is not otherwise specified, accrued interest on this Note
shall be payable monthly on the first day of each month. If any payment of
principal or interest under this Note shall be payable on a day other than a
day on which the Bank is open for business, this payment shall be extended to
the next succeeding business day and interest shall be payable at the rate
specified in this Note during this extension. A late payment charge equal to 5%
of each late payment may be charged on any payment not received by the Bank
within 10 calendar days after the payment due date, but acceptance of payment
of this charge shall not waive any Default under this Note.

     * See addendum for fixed rate option.

The principal amount payable under this Note shall be the sum of all advances
made by the Bank to or at the request of the undersigned, less principal
payments actually received in cash by the Bank. The books and records of the
Bank shall be the best evidence of the principal amount and the unpaid interest
amount owing at any time under this Note and shall be conclusive absent
manifest error. No interest shall accrue under this Note until the date of the
first advance made by the Bank; after that interest on all advances shall
accrue and be computed on the principal balance outstanding from time to time
under this Note until the same is paid in full.

This Note and any other indebtedness and liabilities of any kind of the
undersigned (or any of them) to the Bank, and any and all modifications,
renewals or extensions of it, whether joint or several, contingent or absolute,
now existing or later arising, and however evidenced (collectively
"Indebtedness") are secured by and the Bank is granted a security interest in
all items deposited in any account of any of the undersigned with the Bank and
by all proceeds of these items (cash or otherwise), all account balances of any
of the undersigned from time to time with the Bank, by all property of any of
the undersigned from time to time in the possession of the Bank and by any
other collateral, rights and properties described in each and every deed of
trust, mortgage, security agreement, pledge, assignment and other security or
collateral agreement which has been, or will at any time(s) later be, executed
by any (or all) of the undersigned to or for the benefit of the Bank
(collectively "Collateral"). Notwithstanding the above, (i) to the extent that
any portion of the Indebtedness is a consumer loan, that portion shall not be
secured by any deed of trust or mortgage on or other security interest in any
of the undersigned's principal dwelling or any of the undersigned's real
property which is not a purchase money security interest as to that portion,
unless expressly provided to the contrary in another place, or (ii) if the
undersigned (or any of them) has (have) given or give(s) Bank a deed of trust
or mortgage covering real property, that deed of trust or mortgage shall not
secure this Note or any other indebtedness of the undersigned (or any of them),
unless expressly provided to the contrary in another place.

If the undersigned (or any of them) or any guarantor under a guaranty of all or
part of the Indebtedness ("guarantor") (i) fail(s) to pay any of the
Indebtedness when due, by maturity, acceleration or otherwise, or fail(s) to
pay any Indebtedness owing on a demand basis upon demand; or (ii) fail(s) to
comply with any of the terms or provisions of any agreement between the
undersigned (or any of them) or any such guarantor and the Bank; or (iii)
become(s) insolvent or the subject of a voluntary or involuntary proceeding in
bankruptcy, or a reorganization, arrangement or creditor composition
proceeding, (if a business entity) cease(s) doing business as a going concern,
(if a natural person) die(s) or become(s) incompetent, (if a partnership)
dissolve(s) or any general partner of it dies, becomes incompetent or becomes
the subject of a bankruptcy proceeding or (if a corporation of a limited
liability company) is the subject of a dissolution, merger or consolidation; or
(a) if any warranty or representation made by any of the undersigned or any
guarantor in connection with this Note or any of the Indebtedness shall be
discovered to be untrue or incomplete; or (b) if there is any termination,
notice of termination, or breach of any guaranty, pledge, collateral assignment
or subordination agreement relating to all or any part of the Indebtedness; or
(c) if there is any failure by any of the undersigned or any guarantor to pay
when due any of its indebtedness (other than to the Bank) or in the observance
or performance of any term, covenant or condition in any document evidencing,
securing or relating to such indebtedness; or (d) if the Bank deems itself
insecure believing that the prospect of payment of this Note or any of the
Indebtedness is impaired or shall fear deterioration, removal or waste of any
of the Collateral; or (e) if there is filed or issued a levy or writ of
attachment or garnishment or other like judicial process upon the undersigned
(or any of them) or any guarantor or any of the Collateral, including without
limit, any accounts of the undersigned (or any of them) or any guarantor with
the Bank, then the Bank, upon the occurrence of any of these events (each a
"Default"), may at its option and without prior notice to the undersigned (or
any of them), declare any or all of the Indebtedness to be immediately due and
payable (notwithstanding any provisions contained in the evidence of it to the
contrary), sell or liquidate all or any portion of the Collateral, set off
against the Indebtedness any amounts owing by the Bank to the undersigned (or
any of them), charge interest at the default rate provided in the document
evidencing the relevant Indebtedness and exercise any one or more of the rights
and remedies granted to the Bank by any agreement with the undersigned (or any
of them) or given to it under applicable law. In addition, if this Note is
secured by a deed of trust or mortgage covering real property, then the trustor
or mortgagor shall not mortgage or pledge the mortgaged premises as security
for any other indebtedness or obligations. This Note, together with all other
indebtedness secured by said deed of trust or mortgage, shall become due and
payable immediately, without notice, at the option of the Bank, (a) if said
trustor or mortgagor shall mortgage or pledge the mortgaged premises (or any
other indebtedness or obligations or shall convey, assign or transfer the
mortgaged premises by deed, installment sale contract instrument, or (b) if the
title to the mortgaged premises shall become vested in any other person or
party in any manner whatsoever, or (c) if there is any disposition (through one
or more transactions) of legal or beneficial title to a controlling interest of
said trustor or mortgagor. All payments under this Note shall be in immediately
available United States funds, without setoff or counterclaim.

If this Note is signed by two or more parties (whether by all as makers or by
one or more as an accommodation party or otherwise), the obligations and
undertakings under this Note shall be that of all and any two or more jointly
and also of each severally. This Note shall bind the undersigned, and the
undersigned's respective heirs, personal representatives, successors and
assigns.

The undersigned waive(s) presentment, demand, protest, notice of dishonor,
notice of demand or intent to demand, notice of acceleration or intent to
accelerate, and all other notices and agree(s) that no extension or indulgence
to the undersigned (or any of them) or release, substitution or nonenforcement
of any security, or release or substitution of any of the undersigned, any
guarantor or any other party, whether with or without notice, shall affect the
obligations of any of the undersigned. The undersigned waive(s) all defenses or
right to discharge available under Section 3-605 of the California Uniform
Commercial Code and waive(s) all other suretyship defenses or right to
discharge. The undersigned agree(s) that the Bank has the right to sell,
assign, or grant participations, or any interest, in any or all of the
Indebtedness, and that, in connection with this right, but without limiting its
ability to make other disclosures to the full extent allowable, the Bank may
disclose all documents and information which the Bank now or later has relating
to the undersigned or the Indebtedness. The undersigned agree(s) that the Bank
may provide information relating to the Note or to the undersigned to the
Bank's parent, affiliates, subsidiaries and service providers.


<PAGE>   2
The undersigned agree(s) to reimburse the holder or owner of this Note for any
and all costs and expenses (including without limit, court costs, legal
expenses and reasonable attorney fees, whether inside or outside counsel is
used, whether or not suit is instituted and, if suit is instituted, whether at
the trial court level, appellate level, in a bankruptcy, probate or
administrative proceeding or otherwise) incurred in collecting or attempting to
collect this Note or incurred in any other matter or proceeding relating to
this Note.

The undersigned acknowledge(s) and agree(s) that there are no contrary
agreements, oral or written, establishing a term of this Note and agree(s) that
the terms and conditions of this Note may not be amended, waived or modified
except in a writing signed by an officer of the Bank expressly stating that the
writing constitutes an amendment, waiver or modification of the terms of this
Note. As used in this Note, the word "undersigned" means, individually and
collectively, each maker, accommodation party, indorser and other party signing
this Note in a similar capacity. If any provision of this Note is unenforceable
in whole or part for any reason, the remaining provisions shall continue to be
effective. THIS NOTE IS MADE IN THE STATE OF CALIFORNIA AND SHALL BE GOVERNED
BY AND CONSTRUED IN ACCORDANCE WITH THE INTERNAL LAWS OF THE STATE OF
CALIFORNIA, WITHOUT REGARD TO CONFLICT OF LAWS PRINCIPLES.

The maximum interest rate shall not exceed the highest applicable usury ceiling.

See Addendum and LIBOR Addendum.

THE UNDERSIGNED AND THE BANK ACKNOWLEDGE THAT THE RIGHT TO TRIAL BY JURY IS A
CONSTITUTIONAL ONE, BUT THAT IT MAY BE WAIVED, EACH PARTY, AFTER CONSULTING (OR
HAVING HAD THE OPPORTUNITY TO CONSULT) WITH COUNSEL OF THEIR CHOICE, KNOWINGLY
AND VOLUNTARILY AND FOR THEIR MUTUAL BENEFIT, WAIVES ANY RIGHT TO TRIAL BY JURY
IN THE EVENT OF LITIGATION REGARDING THE PERFORMANCE OR ENFORCEMENT OF, OR IN
ANY WAY RELATED TO, THIS NOTE OR THE INDEBTEDNESS.


JMAR TECHNOLOGIES, INC.

By: /s/ DENNIS E. VALENTINE               Its: Chief Financial Officer
   -------------------------------          -------------------------------
   SIGNATURE OF                             TITLE

By:                                     Its:
   -------------------------------          -------------------------------
   SIGNATURE OF                             TITLE

By:                                     Its:
   -------------------------------          -------------------------------
   SIGNATURE OF                             TITLE

By:                                     Its:
   -------------------------------          -------------------------------
   SIGNATURE OF                             TITLE

Comerica Bank
 /s/ BROCK MULLINS                      Its: Assistant Vice President
--------------------------                  -------------------------------
Signature of Brock Mullins                  Title









<TABLE>
<S>                                     <C>                 <C>             <C>           <C>
9207 ETON AVENUE                        CHATSWORTH          CALIFORNIA      USA           91311
----------------------------------------------------------------------------------------------------
STREET ADDRESS                          CITY                STATE           COUNTRY      ZIP CODE


                              For Bank Use Only                CCAR #
----------------------------------------------------------------------------------------------------
Loan Officer Initials    Loan Group Name              Obligor(s) Name
BM                       WESTWOOD MIDDLE MARKET       JMAR TECHNOLOGIES, INC.
----------------------------------------------------------------------------------------------------
Loan Officer I.D. No.    Loan Group No.               Obligor #                Note #     Amount 
48234                    96551                                                            $5,000,000.00
</TABLE>


CA 00184.1 (12-94)
<PAGE>   3
                       ADDENDUM TO MASTER REVOLVING NOTE
                       ---------------------------------

      This ADDENDUM TO MASTER REVOLVING NOTE (This "Addendum"), dated June 26,
1998, shall be a part of and is hereby incorporated into that certain Master
Revolving Note of even date herewith (the "Note"), executed by JMAR
Technologies, Inc. ("Borrower") in favor of Comerica Bank - California
("Bank"). All initially capitalized terms used but not defined in this addendum
shall have the meanings assigned to such terms in the Note. Borrower hereby
agrees that the following terms and conditions shall be incorporated into the
Note:

1. DEFINITIONS.
      
      1.1   DEFINED TERMS. As used in this Addendum, the following terms shall
have the following respective meanings:

      "Current Assets" shall mean, as of any applicable date of determination,
all cash, non-affiliated customer receivables, United States government
securities, claims against the United States government, and inventories.

      "Current Liabilities" shall mean, as of any applicable date of
determination, (i) all liabilities of a person that should be classified as
current in accordance with GAAP, including without limitation any portion of
the principal of the indebtedness classified as current, plus (ii) to the
extent not otherwise included, all liabilities of the Borrower to any of its
affiliates whether or not classified as current in accordance with GAAP.

      "Debt" shall mean, as of any applicable date of determination, all items
of indebtedness, obligation or liability of the Borrower, whether matured or
unmatured, liquidated or unliquidated, direct or indirect, absolute or
contingent, joint or several, that should be classified as liabilities in
accordance with GAAP.

      "Effective Tangible Net Worth" shall mean, as of any applicable date of
determination, the excess of (i) the net book value of all assets of the
Borrower (other than patents, patent rights, trademarks, trade names,
copyrights, licenses, goodwill, Employee Stock Ownership Plan receivables, and
similar intangible assets) after all appropriate deductions in accordance with
GAAP (including, without limitation, reserves for doubtful receivables,
obsolescence, depreciation and amortization), over (ii) all debt of the
Borrower, increased by (iii) subordinated debt if any. 

      "Event of Default" or "Default" shall have the meaning set forth in the
Note and in the Security Agreement (All Assets) dated June 26, 1998 executed by
JMAR Technologies, Inc. in

                                       1
<PAGE>   4

favor of Comerica Bank-California.

     "Financial Statements" shall mean all those balance sheets, income
statements and other financial data (whether of the Borrower, any of its
subsidiaries or otherwise) which have been furnished to the Bank for the
purposes of, or in connection with, this Agreement and the transactions
contemplated hereby.

     "GAAP" shall mean, as of any applicable date of determination, generally
accepted accounting principles consistently applied.

     "Guarantor" shall mean any individual who has signed and executed a
Guaranty document with the Bank in form and content satisfactory to the Bank.

     "Net Income" shall mean the net income (or loss) of the Borrower for any
period determined in accordance with GAAP.

     "Subordinated Debt" shall mean indebtedness of the Borrower to third
parties which has been subordinated to the Bank pursuant to a subordination
agreement in form and content satisfactory to the Bank.

     "Subsidiaries" shall mean JMAR Precision Systems Inc., JMAR Semiconductor
Inc., JMAR Research Inc., and any other entities owned by JMAR Technologies Inc.

2. Affirmative Covenants.

     On a continuing basis from the date of this Addendum until the later of the
Maturity Date or when the indebtedness is paid in full and the Borrower has
performed all of its other obligations hereunder, the Borrower covenants and
agrees that it will:

     2.1 Financial and Other Information.

     2.1.1 Annual Financial Reports. Furnish to the Bank, in form and reporting
basis satisfactory to the Bank, not later than ninety (90) days after the close
of each fiscal year of the Borrower, beginning with the fiscal year ending
December 31, 1998, financial statements of the Borrower and Subsidiaries on a
consolidated and consolidating basis containing the income statement and balance
sheet of the Borrower and Subsidiaries and a statement of cash flows for each
such fiscal year, and such other comments and financial details as are usually
included in similar reports. Such reports shall be prepared in accordance with
GAAP by independent certified public accountants of recognized standing selected
by the Borrower and acceptable to the Bank and shall be on an audited basis with
an unqualified opinion.

     2.1.2 Quarterly Financial Statements. Furnish to the Bank not later than
thirty (30) days after the close of each quarter of each fiscal year of the
Borrower, beginning with the fiscal


                                       2
<PAGE>   5
quarter ending June 30, 1998, financial statements of the Borrower and
Subsidiaries on a consolidated and consolidating basis containing the income
statement and balance sheet of the Borrower and Subsidiaries as of the end of
each such period, and such other comments and financial details as are usually
included in similar reports. These statements shall be company-prepared on the
same accounting basis as the statements required in section 2.1.1 of this
Agreement and shall be in such detail as the Bank may reasonably require, and
the accuracy of the statements shall be certified by the Borrower.

     2.1.3 Aging of Accounts Receivable. Furnish to the Bank quarterly by the
15th day of the first month of each fiscal quarter an aging as of the end of the
preceding month of Borrower's Accounts Receivable in a form satisfactory to the
Bank.

     2.1.4 Aging of Accounts Payable. Furnish to the Bank quarterly by the 15th
day of the first month of each fiscal quarter an aging as of the end of the
preceding month of Borrower's Accounts Payable in a form satisfactory to the
Bank

     2.1.5 No Default Certificate. Together with each delivery of the financial
statements required by Sections 2.1.1 and 2.1.2 of this Agreement, furnish to
the Bank a certificate stating that no Event of Default or Default has occurred,
or if any such Event of Default or Default exists, stating the nature thereof,
the period of existence thereof and what action the Borrower proposes to take
with respect thereto.

     2.1.6 Maintain Debt Ratio. On a consolidated basis, maintain the ratio of
its Debt (less debt subordinated to the Bank) to Effective Tangible Net Worth at
not more than the 1.25:1 at all times.

     2.1.7 Maintain Effective Tangible Net Worth. On a consolidated basis,
maintain Effective Tangible Net Worth of not less than $7,500,000 at all times.

     2.1.8 Maintain Annual Net Income. On a consolidated basis, maintain annual
Net Income after tax of not less than $1,000,000.

     2.1.9 Maintain Quarterly Net Income. On a consolidated basis, maintain
quarterly Net Income after tax of not less than $0.

     2.1.10 Maintain current ratio. On a consolidated basis, maintain a ratio of
Current Assets to Current Liabilities of not less than 1.75:1.

3. Advances

     3.1 Advances on the Note are allowed to be made directly to JMAR
Technologies Inc. and JMAR Precision Systems, Inc.


                                       3
<PAGE>   6
     3.2  Maximum Advances. Advances made on the Note by JMAR Technologies Inc.
and transferred or loaned to subsidiaries other than JMAR Precision Systems
shall be limited to a maximum aggregate of $1,500,000.

4.   Guarantees

     The Note shall be supported by secured guarantees from JMAR Precision
Systems, Inc., JMAR Research, Inc. and JMAR Semiconducer, Inc.

     IN WITNESS WHEREOF, Borrowers have executed this Addendum as of the date
first above written.

JMAR Technologies, Inc.                 Comerica Bank - California


  /s/ Dennis E. Valentine                  /s/ Brock Mullins
---------------------------------       ---------------------------------








                                       4
<PAGE>   7
[COMERICA LOGO]

                      VARIABLE RATE - SINGLE PAYMENT NOTE


--------------------------------------------------------------------------------
AMOUNT             NOTE DATE            MATURITY DATE       TAX IDENTIFICATION #

$1,000,000.00      June 25, 1998        June 01, 1999
--------------------------------------------------------------------------------


On the Maturity Date, as stated above, for value received, the undersigned
promise(s) to pay to the order of Comerica Bank-California ("Bank"), at any
office of the Bank in the State of California, One Million and no/100 Dollars
(U.S.) with interest from the date of this Note at a per annum rate equal to
the Bank's base rate from time to time in effect plus 0.000% per annum until
maturity, whether by acceleration or otherwise, or until Default, as later
defined, and after that at a default rate equal to the rate of interest
otherwise prevailing under this Note plus 3% per annum (but in no event in
excess of the maximum rate permitted by law). The Bank's "base rate" is that
annual rate of Interest so designated by the Bank and which is
changed by the Bank from time to time. Interest rate changes will be effective
for interest computation purposes as and when the Bank's base rate changes.
Interest shall be calculated for the actual number of days the principal is
outstanding on the basis of a 360-day year if this Note evidences a business or
commercial loan or a 365-day year if a consumer loan. Accrued interest on this
Note shall be payable on either (i) [ ] the Maturity Date or (ii) [X] the 1st
day of each month commencing August 01, 1998, until the Maturity Date when all
amounts outstanding under this Note shall be due and payable in full. If the
frequency of interest payments is not otherwise specified, accrued interest on
this Note shall be payable monthly on the first day of each month. If any
payment of principal or interest under this Note shall be payable on a day
other than a day on which the Bank is open for business, this payment shall be
extended to the next succeeding business day and interest shall be payable at
the rate specified in this Note during this extension. A late payment charge
equal to 5% of each late payment may be charged on any payment not received by
the Bank within 10 calendar days after the payment due date, but acceptance of
payment of this charge shall not waive any Default under this Note.

This Note and any other indebtedness and liabilities of any kind of the
undersigned (or any of them) to the Bank, and any and all modifications,
renewals or extensions of it, whether joint or several, contingent or absolute,
now existing or later arising, and however evidenced (collectively
"Indebtedness") are secured by and the Bank is granted a security interest in
all items deposited in any account of any of the undersigned with the Bank and
by all proceeds of these items (cash or otherwise), all account balances of any
of the undersigned from time to time with the Bank, by all property of any of
the undersigned, from time to time in the possession of the Bank and by any
other collateral, rights and properties described in each and every deed of
trust, mortgage, security agreement, pledge, assignment and other security or
collateral agreement which has been, or will at any time(s) later be, executed
by and (or all) of the undersigned to or for the benefit of the Bank
(collectively "Collateral"). Notwithstanding the above, (i) to the extent that
any portion of the Indebtedness is a consumer loan, that portion shall not be
secured by any deed of trust or mortgage on or other security interest in any
of the undersigned's principal dwelling or in any of the undersigned's real
property which is not a purchase money security interest as to that portion,
unless expressly provided to the contrary in another place, or (ii) if the
undersigned (or any of them) has (have) given or give(s) Bank a deed of trust
or mortgage covering real property, that deed of trust or mortgage shall not
secure this Note or any other indebtedness of the undersigned (or any of them),
unless expressly provided to the contrary in another place.

If the undersigned (or any of them) or any guarantor under a guaranty of all or
part of the Indebtedness ("guarantor") (i) fail(s) to pay any of the 
Indebtedness when due, by maturity, acceleration or otherwise, or fail(s) to
pay any Indebtedness owing on a demand basis upon demand; or (ii) fail(s) to
comply with any of the terms or provisions of any agreement between the 
undersigned (or any of them) or any guarantor and the Bank; or (iii) become(s)
insolvent or the subject of a voluntary or involuntary proceeding in 
bankruptcy, or a reorganization, arrangement or creditor composition
proceeding, (if a business entity) cease(s) doing business as a going concern,
(if a natural person) die(s) or become(s) incompetent, (if a partnership)
dissolve(s) or any general partner of it dies or becomes incompetent or becomes
the subject of a bankruptcy proceeding or (if a corporation or a limited
liability company) is the subject of a dissolution, merger or consolidation; or
(a) if any warranty or representation made by any of the undersigned or any
guarantor in connection with this Note or any of the Indebtedness shall be
discovered to be untrue or incomplete; or (b) if there is any termination,
notice of termination, or breach of any guaranty, pledge, collateral assignment
or subordination agreement relating to all or any part of the Indebtedness; or
(c) if there is any failure by any of the undersigned or any guarantor to pay
when due any of its indebtedness (other than to the Bank) or in the observance
or performance of any term, covenant or condition in any document evidencing,
securing or relating to such indebtedness; or (d) if the Bank deems itself
insecure believing that the prospect of payment of this Note or any of the
Indebtedness is impaired or shall fear deterioration, removal or waste of any
of the Collateral; or (e) if there is filed or issued a levy or writ of
attachment or garnishment or other like judicial process upon the undersigned
(or any of them) or any guarantor or any of the Collateral, including without
limit, any accounts of the undersigned (or any of them) or any guarantor with
the Bank, then the Bank, upon the occurrence of any of these events (each a
"Default"), may at its option and without prior notice to the undersigned (or
any of them); declare any or all of the Indebtedness to be immediately due and
payable (notwithstanding any provisions contained in the evidence of it to the
contrary), sell or liquidate all or any portion of the Collateral, set off
against the Indebtedness any amounts owing by the Bank to the undersigned (or
any of them), charge interest at the default rate provided in the document
evidencing the relevant Indebtedness and exercise any one or more of the rights
and remedies granted to the Bank by any agreement with the undersigned (or any
of them) or given to it under applicable law. In addition, if this Note is
secured by a deed of trust or mortgage covering real property, then the trustor
or mortgagor shall not mortgage or pledge the mortgaged premises as security
for any other indebtedness or obligations. This Note, together with all other
indebtedness secured by said deed of trust or mortgage, shall become due and
payable immediately, without notice, at the option of the Bank, (a) if said
trustor or mortgagor shall mortgage or pledge the mortgaged premises for any
other indebtedness or obligations or shall convey, assign or transfer the
mortgaged premises by deed, installment sale contract or other instrument, or
(b) if the title to the mortgaged premises shall become vested in any other
person or party in any manner whatsoever, or (c) if there is any disposition
(through one or more transactions) of legal or beneficial title to a
controlling interest of said trustor or mortgagor. All payments under this Note
shall be in immediately available United States funds, without setoff or
counterclaim.

If this Note is signed by two or more parties (whether by all as makers or by
one or more as an accommodation party or otherwise), the obligations and
undertakings under this Note shall be that of all and any two or more jointly
and also of each severally. This Note shall bind the undersigned, and
the undersigned's respective heirs, personal representatives, successors and
assigns.

The undersigned waive(s) presentment, demand, protest, notice of dishonor,
notice of demand or intent to demand, notice of acceleration or intent to
accelerate, and all other notices, and agree(s) that no extension or indulgence
to the undersigned (or any of them) or release, substitution or nonenforcement
of any security, or release or substitution of any of the undersigned, any
guarantor or any other party, whether with or without notice, shall affect the
obligations of any of the undersigned. The undersigned waive(s) all defenses or
right to discharge available under Section 3-605 of the California Uniform
Commercial Code and waive(s) all other suretyship defenses on right to
discharge. The undersigned agree(s) that the Bank has the right to sell,
assign, or grant participations, or any interest, in any or all of the
Indebtedness, and that, in connection with this right, but without limiting its
ability to make other disclosures to the full extent allowable, the Bank may
disclose all documents and information which the Bank now or later has relating
to the undersigned or the Indebtedness. The undersigned agree(s) that the Bank
may provide information relating to this Note or to the undersigned to the
Bank's parent, affiliates, subsidiaries and service providers.

The undersigned agree(s) to reimburse the holder or owner of this Note for any
and all costs and expenses (including without limit, court costs, legal expenses
and reasonable attorney fees, whether inside or outside counsel is used, whether
or not the suit is instituted and, if suit is instituted, whether at the trial
court level, appellate level, in a bankruptcy, probate or administrative
proceeding or otherwise) incurred in collecting or attempting to collect this
Note or incurred in any other matter or proceeding relating to this Note.
<PAGE>   8
The undersigned acknowledge(s) and agree(s) that there are no contrary
agreements, oral or written, establishing a term of this Note and agree(s) that
the terms and conditions of this Note may be amended, waived or modified except
in a writing signed by an officer of the Bank expressly stating that the writing
constitutes an amendment, waiver or modification of the terms of this Note. As
used in this Note, the word "undersigned" means, individually and collectively,
each maker, accommodation party, indorser and other party signing this Note in a
similar capacity. If any provision of this Note is unenforceable in whole or
part for any reason, the remaining provisions shall continue to be effective.
THIS NOTE IS MADE IN THE STATE OF CALIFORNIA AND SHALL BE GOVERNED BY AND
CONSTRUED IN ACCORDANCE WITH THE INTERNAL LAWS OF THE STATE OF CALIFORNIA,
WITHOUT REGARD TO CONFLICT OF LAWS PRINCIPLES.

The maximum interest rate shall not exceed the highest applicable usury ceiling.

THE UNDERSIGNED AND THE BANK ACKNOWLEDGE THAT THE RIGHT TO TRIAL BY JURY IS A
CONSTITUTIONAL ONE, BUT THAT IT MAY BE WAIVED EACH PARTY, AFTER CONSULTING (OR
HAVING HAD THE OPPORTUNITY TO CONSULT) WITH COUNSEL OF THEIR CHOICE, KNOWINGLY
AND VOLUNTARILY AND FOR THEIR MUTUAL BENEFIT, WAIVES ANY RIGHT TO TRIAL BY JURY
IN THE EVENT OF LITIGATION REGARDING THE PERFORMANCE OR ENFORCEMENT OF, OR IN
ANY WAY RELATED TO, THIS NOTE OR THE INDEBTEDNESS.

See Addendum.

JMAR TECHNOLOGIES, INC.

By: /s/ DENNIS E. VALENTINE            Its: Chief Financial Officer
   -------------------------------          -------------------------------
   SIGNATURE OF                             TITLE

By:                                     Its:
   -------------------------------          -------------------------------
   SIGNATURE OF                             TITLE

By:                                     Its:
   -------------------------------          -------------------------------
   SIGNATURE OF                             TITLE

By:                                     Its:
   -------------------------------          -------------------------------
   SIGNATURE OF                             TITLE

Comerica Bank
 /s/ BROCK MULLINS                      ITS: Assistant Vice President
--------------------------                  -------------------------------
Signature of Brock Mullins                  Title










<TABLE>
<S>                                     <C>                 <C>             <C>           <C>
9207 ETON AVENUE                        CHATSWORTH          CALIFORNIA      USA           91311
--------------------------------------------------------------------------------------------------------
STREET ADDRESS                          CITY                STATE            COUNTRY      ZIP CODE


                              For Bank Use Only                CCAR #
--------------------------------------------------------------------------------------------------------
Loan Officer Initials    Loan Group Name              Obligor(s) Name
BM                       WESTWOOD MIDDLE MARKET       JMAR TECHNOLOGIES, INC.
--------------------------------------------------------------------------------------------------------
Loan Officer I.D. No.    Loan Group No.               Obligor #                Note #     Amount 
48234                    96551                                                            $1,000,000.00
</TABLE>


CA 00179 (9/95)
<PAGE>   9


            ADDENDUM TO $1,000,000 VARIABLE RATE-SINGLE PAYMENT NOTE


     This ADDENDUM TO VARIABLE RATE-SINGLE PAYMENT NOTE (This "Addendum"), dated
June 25, 1998, shall be a a part of and is hereby incorporated into that certain
Variable Rate-Single Payment Note of even date herewith (the "Note"), executed
by JMAR Technologies, Inc. ("Borrower") in favor of Comerica Bank-California
("Bank"). All initially capitalized terms used but not defined in this addendum
shall have the meanings assigned to such terms in the Note. Borrower hereby
agrees that the following terms and conditions shall be incorporated into the
Note:

1. USE OF FUNDS. Advances under the Note shall be used to finance 80% of the
total cost of new equipment. Borrower may also use the Note to finance 70% of
the total cost of demo inventory at JMAR Precision Systems, Inc.

2. ISSUANCE OF TERM NOTE. On 6/1/99 (the "Conversion Date"), the Borrower shall
execute and deliver to the Bank a term note (a "Term Note") consistent with the
Bank's then standard forms, in an aggregate principal amount equal to the
outstanding principal balance on the Note. The Term Note shall have a maturity
date that is 48 months from the date of its issuance. The outstanding principal
of the Term Note shall bear interest at the variable rate equal to the Bank's
base rate, or upon the request of the Borrower a fixed rate of interest equal to
two and one-half percent above Bank's Cost of Funds as determined on the
Conversion Date, and such interest shall be payable on the same dates on which
interest is payable under the Note. Principal shall be payable concurrently with
interest, in substantially equal installments such that the Term Note will be
fully amortized by its maturity date. The Term Note shall contain the same
covenants, conditions, and Defaults as are contained in the Note (including this
Addendum), and shall have the benefit of all collateral, guaranties and
subordination agreements in favor of the Note.

3. ADVANCES. Advances on the Note are allowed to be made directly to JMAR
Technologies, Inc. And JMAR Precision Systems, Inc.

     IN WITNESS WHEREOF, Borrowers have executed this Addendum as of the date
first above written.

JMAR Technologies, Inc.                 Comerica Bank-California


/s/ JOHN S. MARTINEZ                    /s/ BROCK MULLINS
-----------------------                 -------------------------


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