<PAGE>

                                                                   Exhibit 10.36

                   CONFIDENTIAL TREATMENT HAS BEEN SOUGHT FOR
                 PORTIONS OF THIS EXHIBIT PURSUANT TO RULE 24B-2
              UNDER THE SECURITIES EXCHANGE ACT OF 1934, AS AMENDED

                              [Photogen Letterhead]

January 18, 2000

BY FAX (408/764-4850) AND FEDERAL EXPRESS

Coherent Laser Group
5100 Patrick Henry Drive
Santa Clara, CA 95054

Attention:  Mr. Michael Armas

RE: COHERENT SOFTWARE DISTRIBUTION AGREEMENT ("DISTRIBUTION AGREEMENT")

Dear Mr. Armas:

          This letter sets out the agreement between Photogen, Inc. ("Photogen")
and the Laser Group of Coherent, Inc. ("Coherent") regarding a license to
distribute certain software Photogen developed.

1.       This Distribution Agreement applies to the software product described
         in Exhibit A to this letter, together with the documentation Photogen
         provides with that software for distribution to end users and any
         maintenance modifications that correct errors resulting from incorrect
         operation of the object code of that software (the "Software"). The
         Software does not include any update, new version or enhancement unless
         Photogen, in its sole discretion, adds that item and related fees to
         Exhibit A. A "Software Copy" is an exact object code copy of the
         Software in machine readable form, together with an exact copy of the
         end-user documentation included in the definition of the Software, made
         by or on behalf of Photogen. Software Copies may be sold in disk form
         or as part of a software/interface hardware package.

2.       Photogen grants to Coherent a license: (a) to license Software Copies
         for use only with laser systems manufactured by Coherent or other laser
         manufacturers ("Laser Systems") and only directly to end-user customers
         who will use the software only for qualitative purposes; (b) to use the
         Software only to test or demonstrate Laser Systems to prospective end
         users; and (c) to use Photogen's service marks and trademarks
         designated on Exhibit A to market the Software in accordance with
         Photogen's prior written approval. Coherent may license the Software to
         end users outside the United States, provided Coherent (at its own
         expense) demonstrates


<PAGE>


Coherent Software Distribution Agreement
January 18, 2000
Page 2 of 6

         compliance with applicable legal and regulatory requirements, such as
         necessary export licensing.

3.       The license granted to Coherent in paragraph 2 is exclusive; except
         that (a) if Coherent fails to meet the "Minimum Performance Criteria"
         in Exhibit A, the license will become non-exclusive with respect to
         Coherent upon written notice by Photogen; and (b) Photogen reserves for
         itself the right to use the Software for research, development and
         similar activities Photogen conducts or engages third parties to
         conduct and reserves all other rights not expressly granted to Coherent
         in this Distribution Agreement.

4.       Under all circumstances, as between the parties, Photogen retains: (a)
         all title to and (except as expressly licensed herein) all rights to
         the Software, all copies and derivative works thereof (by whomever
         produced) and all related documentation and materials; (b) all of its
         service marks, trademarks, tradenames or any other designations; (c)
         all copyrights, patent rights, trade secret rights, and all other
         intellectual and industrial property rights of any sort in the
         Software.

5.       Coherent will not distribute or license a Software Copy except pursuant
         to an enforceable End User License Agreement signed by the end user in
         the form set forth in Exhibit B hereto or a shrink-wrap or "click-on"
         version of the same agreement that is packaged and delivered to the end
         user in the manner specified by Photogen in writing. If a shrink-wrap
         or click-on agreement is used, Coherent will accept returns in
         accordance with the procedure specified in the packaging accompanying
         the Software Copy.

6.       Software Copies are delivered F.O.B. Photogen's principal office in
         Knoxville, Tennessee. Coherent will pay Photogen the Unit Price for
         each Software Copy as set forth in Exhibit A. Coherent will also pay
         all charges, including transportation charges and insurance premiums
         and shall be responsible for all taxes (except Photogen's U.S. income
         taxes) in connection with the subject matter of this Distribution
         Agreement, duties and other governmental assessments. Coherent will
         provide Photogen with quarterly nonbinding good faith forecasts of its
         anticipated requirements for Software Copies and shipping dates for the
         6-month periods following those forecasts.

7.       During the term of this Distribution Agreement, Photogen will: (a)
         inform Coherent within a reasonable time of any substantive changes in
         the Software or delivery schedules; (b) provide Coherent the most
         current commercial release or version of the Software; (c) use its
         reasonable efforts to fill (by full or partial shipment) Coherent's
         orders for Software Copies, which are accepted by Photogen at its main
         office (which acceptance will not be unreasonably withheld) within 60
         days after receipt of order insofar as practicable and consistent with
         Photogen's then-current lead-time schedule, shipping schedule, and
         access to supplies on acceptable terms; (d) provide one standard
         training program for Coherent personnel at Coherent's main office on a
         schedule reasonably acceptable to the parties; and (e) use its
         reasonable efforts to provide


<PAGE>


Coherent Software Distribution Agreement
January 18, 2000
Page 3 of 6

         support and maintenance services relating to the Software directly to
         Coherent, but not to end users, during the term of this Distribution
         Agreement.

8.       Coherent represents and warrants to, and agrees with Photogen, that
         Coherent will:

         (a)      not modify, create any derivative work of, or include in any
                  other software or make any copies of the Software or any
                  portion thereof;

         (b)      not delete, alter, obscure, add to or fail to reproduce in and
                  on any Software Copy and media the name of the Software and
                  any copyright, trademark, patent or other notices appearing in
                  or on any copy, media or master or package materials provided
                  by Photogen or which may be required by Photogen at any time;

         (c)      not reverse assemble, decompile, reverse engineer or otherwise
                  attempt to derive source code (or the underlying ideas,
                  algorithms, structure or organization) from the Software or
                  from any other information;

         (d)      use its best efforts to successfully market, distribute, and
                  support Software Copies within the scope of the license in
                  paragraph 2, including through (i) Coherent affiliates (as
                  defined in regulations under the Securities Exchange Act of
                  1934), and (ii) agents and sublicensees that Photogen approves
                  in its sole discretion in writing prior to their appointment
                  by Coherent;

         (e)      use the designated trademarks and other names associated with
                  the Software, it being agreed that such use (and any related
                  goodwill) shall be solely for Photogen's benefit; and Coherent
                  will not otherwise use or register (or make any filing with
                  respect to) any trademark, name or other designation or
                  copyrightable works relevant to the subject matter of this
                  Distribution Agreement anywhere in the world; and will not
                  contest anywhere in the world the use by or authorized by
                  Photogen of any trademark, name or other designation or
                  copyright relevant to the subject matter of this Distribution
                  Agreement or application or registration therefore, during the
                  term of this Distribution Agreement;

         (f)      keep Photogen informed as to any problems encountered with the
                  Software and any resolutions arrived at for those problems,
                  and communicate promptly to Photogen any and all
                  modifications, design changes or improvements of the Software
                  suggested by any end user, customer, employee, sublicensee or
                  agent; it being agreed by Coherent that Photogen shall have
                  and is hereby assigned any and all right, title, and interest
                  in and to any such suggested modifications, design changes, or
                  improvements of the Software, without the payment of any
                  additional consideration therefore either to Coherent, or its
                  employees, agents or customers and that Coherent will fully
                  cooperate with Photogen in this regard;


<PAGE>


Coherent Software Distribution Agreement
January 18, 2000
Page 4 of 6

         (g)      maintain a file of the name and address of all persons and
                  entities to which it distributes a Software Copy, the serial
                  number designation of the Software Copy, the date of delivery
                  and the End User License Agreement, and any other information
                  necessary to calculate payments due Photogen under this
                  Distribution Agreement; and permit Photogen or its
                  representative to examine and audit those records, records
                  relevant to license fees and any related records during
                  reasonable business hours (and Coherent will pay Photogen's
                  audit expenses if the audit uncovers a 5% or more deficiency
                  in payments);

         (h)      comply with applicable U.S. and foreign laws and regulations
                  covering its activities under this Distribution Agreement, and
                  not export or re-export, or allow the export or re-export of
                  any product, technology or information it obtains or learns
                  pursuant to this Distribution Agreement (or any direct product
                  thereof) in violation of this Distribution Agreement and any
                  such laws, restrictions or regulations; and

         (i)      use, in addition to and without in any way limiting Coherent's
                  other obligations hereunder, all methods to protect Photogen's
                  rights with respect to the Software, Software Copies and
                  Proprietary Information as Coherent uses to protect its own or
                  any third party's software, confidential information or rights
                  of a similar nature.

9.       It is anticipated that during the term of this Distribution Agreement
         Photogen shall disclose proprietary information to Coherent. The
         parties agree that the disclosure of such proprietary information shall
         be governed by the terms of the Proprietary Information Agreement
         attached hereto as Exhibit C.

10.      This Distribution Agreement will be in effect for a term of two years
         from the date of Coherent's acceptance and will automatically terminate
         unless: (a) it is renewed by a written agreement executed by both
         parties expressly providing for renewal; or (b) Coherent meets the
         performance criteria specified in Exhibit A, Unilateral Extension
         Performance Criteria. Photogen may terminate this Distribution
         Agreement at any time during the term upon written notice to Coherent
         if Coherent: (c) files or becomes subject to a petition under the U.S.
         Bankruptcy Code or becomes insolvent; (d) sells, distributes or
         otherwise disposes of all or substantially all of its assets, or any
         other change occurs in Coherent's business affairs which has a material
         adverse effect on its ability to perform under this Distribution
         Agreement; (e) fails to pay amounts owed to Photogen in accordance with
         Exhibit A; or (f) commits any material breach or default of any other
         provision of this Distribution Agreement. Termination is not the sole
         remedy under this Distribution Agreement and, whether or not
         termination is effected, all other remedies will remain available.




<PAGE>


Coherent Software Distribution Agreement
January 18, 2000
Page 5 of 6

11.      Upon termination of this Distribution Agreement: (a) all amounts owed
         by Coherent to Photogen will become immediately due and payable; (b)
         Coherent will cease using the trademarks, service marks and other
         designations of Photogen, cease representing itself as a distributor
         and/or licensee of Photogen, and return all property (including
         Proprietary Information and Software Copies) belonging to Photogen; (c)
         Coherent will furnish to Photogen a complete list of all of Coherent's
         end users of the Software; (d) all unfilled orders for Software Copies
         by Coherent will be canceled; and (e) the license in paragraph 2 will
         terminate (but not the End User License Agreement) and Coherent will
         cease distributing or licensing any Software or Software Copies. Except
         for paragraphs 2, 7 and 8(d), the provisions of this Distribution
         Agreement survive termination or expiration of this Distribution
         Agreement.

12.      Except for the warranty made directly to end users in the End User
         License Agreement, PHOTOGEN MAKES NO WARRANTIES TO ANY PERSON WITH
         RESPECT TO THE SOFTWARE OR SOFTWARE COPIES OR ANY SERVICES OR LICENSES
         AND DISCLAIMS ALL IMPLIED WARRANTIES, INCLUDING WITHOUT LIMITATION
         WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
         NON-INFRINGEMENT. Coherent will be responsible for all warranty returns
         from end users and will be entitled only to credit for amounts paid to
         Photogen for properly returned Software Copies that are not replaced.
         However, Photogen will indemnify, defend and hold Coherent harmless
         from and against all claims, allegations, loss, liability (including
         settlement payments), expenses (including reasonable attorneys' fees
         and expenses) Coherent incurs that arise out of or relate to any
         finding by a court of competent jurisdiction that the Software
         infringes on the intellectual property rights of any third party.

13.      Coherent will indemnify, defend and hold Photogen harmless from and
         against all claims, allegations, loss, liability (including settlement
         payments), expenses (including reasonable attorneys' fees and expenses)
         Photogen incurs that arise out of or relate to any breach of this
         Distribution Agreement or other wrongful act or omission by Coherent.
         Coherent will maintain comprehensive general liability insurance
         coverage (which will include products and completed operations hazards)
         with limits of at least $2,000,000 for each occurrence and will name
         Photogen as an additional insured.

14.      Notwithstanding anything to the contrary, Photogen will not be liable
         with respect to any subject matter of this Distribution Agreement under
         any contract, negligence, strict liability or other legal theory (a)
         for any amounts in excess, in the aggregate, of the amounts paid to
         Photogen under this Distribution Agreement, (b) for any incidental or
         consequential damages or for lost data or business interruption, (c)
         for cost of procuring substitute goods, technology or services, or (d)
         for loss or corruption of data or for interruption of use of a Laser
         System.


<PAGE>


Coherent Software Distribution Agreement
January 18, 2000
Page 6 of 6

15.      This Distribution Agreement: (a) does not render Photogen and Coherent
         are partners, joint venturers or agents of the other, and neither party
         will be responsible for the liabilities of the other party; (b) may not
         be assigned or delegated without the prior written consent of the other
         party; (c) will be governed by the internal laws of Tennessee (and not
         the law of conflicts); (d) together with its Exhibits, contains the
         entire agreement of the parties concerning the subject matter hereof
         and supersedes all prior negotiations, representations and agreements;
         and (e) together with its Exhibits, supersedes any inconsistent terms
         in any purchase order or other business form of either party. Notices
         under this Distribution Agreement will be legally effective only if in
         writing and received by the addressee, delivered by a courier service,
         or mailed by certified or registered mail, return receipt requested, or
         faxed to a party at its address set forth on page one of this
         Distribution Agreement. If any provision of this Distribution Agreement
         is held to be illegal or unenforceable, that provision shall be limited
         or eliminated to the minimum extent necessary so that this Distribution
         Agreement shall otherwise remain in full force and effect and
         enforceable.

          Please indicate Coherent's agreement to the foregoing by returning a
countersigned copy of this letter to me.

                                         Photogen, Inc.

                                         By:   /S/ ERIC WACHTER
                                               ---------------------------------
                                         Its:  VICE PRESIDENT AND SECRETARY
                                               ---------------------------------

Accepted and Agreed to:

Coherent, Inc.

By:   /S/ SCOTT MILLER
     ----------------------------
Its:    SR VP
     ----------------------------
Date:   1-19-00
      ---------------------------

<PAGE>



                                                                       EXHIBIT A

                              PRODUCTS AND PRICING

<TABLE>
<CAPTION>
PRODUCT DESCRIPTION                                                                              UNIT PRICE
-------------------                                                                              ----------
<S>                                                                                             <C>
PulseView (-TM-)* ver. 2.6 Software Package (CD-ROM, installation
and user guide) and PulseView (-TM-) Interface Adapter, IST/LSA Ver. 2.6                          $[****]
</TABLE>


                                  PAYMENT TERMS

During the first 90 days of this Distribution Agreement, Coherent will pay the
Unit Price to Photogen as follows: 50% on order and 50% on delivery. Thereafter,
Coherent will pay the Unit Price on terms of 30 days net.

                          MINIMUM PERFORMANCE CRITERIA

Coherent will order no less than 25 Product Units within 90 days of the date of
this Distribution Agreement, and no less than an additional 25 Product Units
after that 90-day period during the Term of Agreement (50 Product Units, in
total, during the Term of Agreement). All Product Units must be ordered in
multiples of 25 Units or more per order.

                    UNILATERAL EXTENSION PERFORMANCE CRITERIA

Coherent may, solely at its discretion, extend this Distribution Agreement for
an additional period up to the specified Term of Agreement upon placement of
orders constituting a cumulative quantity of 400% or more of that specified
under terms of the Minimum Performance Criteria.

                                TERM OF AGREEMENT

The term of this Distribution Agreement shall be two years.

[****]   REPRESENTS MATERIALS WHICH HAS BEEN REDACTED PURSUANT TO A REQUEST FOR
         CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2 UNDER THE SECURITIES
         EXCHANGE ACT OF 1934, AS AMENDED


<PAGE>



                                   TRADEMARKS

PulseView (-TM-)* (U.S. trademark registration pending; name may be subject to
change prior to product release)
Photogen (-TM-) (U.S. trademark registration pending)


<PAGE>



                                                                       EXHIBIT B

                           END-USER LICENSE AGREEMENT

By opening the Software, packaging, clicking on the "license accept" button
during Software installation, or installing, copying or otherwise using the
Software, you agree to be bound by the terms of this EULA. IF YOU DO NOT AGREE
TO THE TERMS OF THIS EULA, WE ARE UNWILLING TO LICENSE THE SOFTWARE TO YOU AND
YOU MUST CLICK ON THE "CANCEL" BUTTON. In that case, you are not permitted to
use or copy the Software, and you must promptly contact Coherent, Inc.
("Coherent") for instructions on return of the product(s) for a refund.

      This End-User License Agreement ("EULA") is a legal agreement between you
(a single entity), a user of PulseView-TM- computer software, the associated
media, certain hardware accompanying the computer software, and any printed
materials (together, the "Software") developed by Photogen, Inc.
("Photogen," "we" or "us").

      1. This EULA grants you a non-sublicensable, nonexclusive right to use the
Software only with a laser or related equipment in accordance with the
documentation accompanying the Software and only for qualitative purposes in
research, development and similar activities. This ELUA does not grant you any
license to use the Software for commercial purposes, including without
limitation, manufacturing, or any purposes for which regulatory approval is
required, for any purposes involving human research or medical treatment, or in
any other way that violates any law or regulation or this EULA. The Software is
not designed or intended for use in environments requiring fail-safe performance
or in any other critical application. The Software has not been tested or
designed for use in medical environments or for any clinical purpose. The data
exhibited by the Software is for qualitative purposes only, and we do not
warrant the accuracy of any such data.

      2. Photogen owns the copyright to the Software. Accordingly, the Software
is protected by copyright laws and international copyright treaties, as well as
other intellectual property laws and treaties. The Software is licensed, not
sold.

      3. Your license to the Software is subject to the following restrictions:

         (a)  As between the parties, Photogen retains all title to and
              ownership of all copyright, patent, trade secret and other
              intellectual property and proprietary rights associated with the
              Software, including all documentation. You may not reverse
              engineer, decompile, or disassemble the Software, or attempt to
              reconstruct or discover any source code or underlying ideas or
              algorithms relating to the Software.

         (b)  The Software is licensed as a single product. Its component parts
              may not be separated or copied for use on more than one computer
              at any one time.

         (c)  You may not rent, lease, lend or otherwise transfer the Software.


<PAGE>







         (d)  Without prejudice to any other rights, Photogen or Coherent may
              terminate your right to use the Software under this EULA if you
              fail to comply with the terms and conditions of this EULA. In that
              event, you must destroy all copies of the Software and all of its
              component parts.

         (e)  Software labeled as an upgrade replaces and/or supplements any
              prior version of the Software. You may use the resulting upgraded
              product only in accordance with the terms of this EULA.

      4. You may copy the Software onto one or more computers but only one copy
of the Software may be used at any one time. You may also make a single back-up
copy of the Software and use that copy solely for archival purposes. Except for
the foregoing, you may not make any other copy or modify any aspect of the
Software, including the printed materials accompanying the Software. All rights
not specifically granted under this EULA are reserved by Photogen.

      5. You will not, directly or indirectly, export or transmit the Software
or related documentation and technical data.

      6. You may use the Software in connection with a government project on the
following terms: As defined in FAR section 2.101, DFAR section
252.227-7014(a)(1) and DFAR section 252.227-7014(a)(5) or otherwise, all
Software and accompanying documentation are "commercial items," "commercial
computer software" and/or "commercial computer-software documentation."
Consistent with DFAR section 227.7202 and FAR section 12.212, any use,
modification, reproduction, release, performance, display, disclosure or
distribution of the Software and documentation by or for the U.S. Government
will be governed solely by the terms of this EULA and will be prohibited except
to the extent expressly permitted by the terms of this EULA. You will ensure
that each copy used or possessed by or for the government is labeled to reflect
the foregoing.

      7. Product support for the Software is not provided by Photogen. For
product support, please refer to your applicable Coherent support contact or
representative.

      8. This EULA will be governed by the internal laws of Tennessee, United
States of America.


<PAGE>



                                LIMITED WARRANTY

      LIMITED WARRANTY. Photogen warrants to you, the end user, that (a) the
Software will perform substantially in accordance with the accompanying written
materials for a period of one (1) year from the date of receipt, and (b) any
Photogen hardware accompanying the Software will be free from defects in
materials and workmanship under normal use and service for a period of one (1)
year from the date of receipt. You must report any problems with the Software or
hardware to Coherent. This Limited Warranty covers only problems reported to
Coherent during the warranty period.

      END USER REMEDIES. Photogen's entire liability and your exclusive remedy
under this Limited Warranty shall be, at Photogen's option, either (a) return of
the price paid for the Software, or (b) repair or replacement of the Software or
hardware that does not meet this Limited Warranty and which is returned to
Coherent with appropriate documents verifying the delivery date. This Limited
Warranty is void if failure of the Software or hardware has resulted from
accident, abuse, misuse or misapplication. Any replacement Software or hardware
will be warranted for the remainder of the original warranty period or thirty
(30) days, whichever is longer.

      NO OTHER WARRANTIES. TO THE MAXIMUM EXTENT PERMITTED BY APPLICABLE LAW,
PHOTOGEN DISCLAIMS ALL OTHER WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING,
BUT NOT LIMITED TO IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
PARTICULAR PURPOSE, NON-INFRINGEMENT AND/OR ACCURACY OF DATA, WITH REGARD TO THE
SOFTWARE, THE ACCOMPANYING WRITTEN MATERIALS, AND ANY ACCOMPANYING HARDWARE.
THIS LIMITED WARRANTY GIVES YOU SPECIFIC LEGAL RIGHTS. YOU MAY HAVE OTHER RIGHTS
WHICH VARY FROM STATE TO STATE.

      NO LIABILITY FOR CONSEQUENTIAL OR PUNITIVE DAMAGES.  To the maximum
extent permitted by applicable law, Photogen will not be liable for any
consequential or punitive damages whatsoever (including, without limitation,
special, incidental, consequential, or indirect damages for personal injury,
loss of profits, business interruption, loss of information, or any other
pecuniary loss) arising out of the use or inability to use the Software, even if
Photogen has been advised of the possibility of such damages. Photogen's entire
monetary liability under any provision of this EULA or otherwise shall be
limited to the amount actually paid by you for the Software and/or Photogen
hardware. Because some states or other local jurisdictions do not allow the
exclusion or limitation of liability for consequential, incidental or punitive
damages, the above limitation may not apply to you.


<PAGE>



                                                                       EXHIBIT C

                        PROPRIETARY INFORMATION AGREEMENT

      WHEREAS, COHERENT, INC., a Delaware corporation, hereinafter referred to
as COHERENT, makes and sells lasers, laser accessories, and laser systems and
medical instrumentation;

      WHEREAS, PHOTOGEN, INC. (hereinafter referred to as PARTY) believes it has
information or ideas relating to its PulseView-TM- software product, including,
without limitation, the computer code, algorithms, know-how related thereto
(hereinafter referred to as Confidential Information), which may assist COHERENT
in connection with the Coherent Software Distribution Agreement between COHERENT
and PARTY dated January 18, 2000 (hereinafter referred to as Distribution
Agreement), and desires to disclose said Confidential Information to COHERENT;

      WHEREAS, COHERENT is willing to receive said Confidential Information
under certain conditions;

      NOW, THEREFORE, in consideration of the promises exchanged herein,
COHERENT and PARTY agree as follows:

      (1) COHERENT will not use said Confidential Information except for
purposes of the Distribution Agreement as set forth hereinabove. COHERENT will
not disclose said Confidential Information and shall restrict access to
Confidential Information to only such authorized employees and other agents who
have a need for access to the Confidential Information in connection with their
activities as contemplated by the Distribution Agreement, and will take all
steps necessary to ensure that such employees and agents comply with the terms
hereof.

      (2) All Confidential Information disclosed hereunder shall be in writing,
marked with the word CONFIDENTIAL, SECRET, or PROPRIETARY and dated in the first
instance or, if oral, shall be promptly confirmed in writing, marked with the
word CONFIDENTIAL and dated. This Agreement shall not apply to Confidential
Information disclosed after the date hereof in writing, not marked as set forth
herein or to Confidential Information disclosed after the date hereof orally and
not confirmed in writing and marked within thirty (30) days of the initial oral
disclosure. This Agreement shall also apply to Confidential Infomration
disclosed after February 25, 1999 which otherwise falls within the definition as
set forth herein and which is marked CONFIDENTIAL or confirmed in writing and so
marked within thirty (30) days after the date hereof.

      (3) The commitments set forth in (1) above shall not extend to any
 disclosure of Confidential Information:

         (a)  Which is generally available to the public prior to its
disclosure; or

         (b) Which is known to COHERENT prior to the disclosure thereof as
evidenced by written


<PAGE>



and dated material in its possession; or

         (c) Which, through no fault of COHERENT (including its agents,
representatives, and / or employees), becomes available to the public after the
disclosure hereof; or

         (d) Which is disclosed to COHERENT by a third party having a bona fide
right to do so; or

         (e) Which is approved for release by the written authorization of
PARTY; or

         (f) Which is disclosed pursuant to the requirement of a government
agency or by operation of law, provided COHERENT notifies PART of such
requirement and provides reasonable cooperation with PARTY'S efforts to restrict
such disclosure; or

         (g) Which is developed by COHERENT completely independent of
Confidential Information provided under this Agreement as evidenced by
COHERENT's written records or other competent written evidence;

         (h) Which becomes available to the public despite COHERENT having taken
the same level of care to safeguard said Confidential Information as it would
its own proprietary information; or

         (i) Which is more than five years after the date of initial disclosure.

      (4) This Agreement covers only information disclosed during the term of
the Distribution Agreement. In the event of any inconsistency between the terms
of this Agreement and the Distribution Agreement, the provisions of the
Distribution Agreement shall control.

      (5) COHERENT acknowledges that unauthorized disclosure or use of
Confidential Information could cause irreparable harm and significant injury to
PARTY, the amounts of which would be difficult to ascertain. Accordingly,
COHERENT agrees that PARTY shall have the right to seek and obtain immediate
injunctive relief from breaches of this Agreement, in addition to any other
rights and remedies it may have.

      (6) PARTY represents that it has the legal right to make disclosures of
Confidential Information under this Agreement.

      (7) No representation or warranty is made as to the accuracy, completeness
or technical or scientific quality of the Confidential Information disclosed
hereunder.

      (8) This Agreement shall be deemed to have been entered into and shall be
construed in accordance with the laws of the State of California.

      (9) Any materials or documents of PARTY which have been furnished to
COHERENT will be promptly returned to PARTY upon PARTY's request. Historical
information copies may be kept by the Party's attorney for purposes of file
continuity. COHERENT's attorney shall provide PARTY written confirmation of the
receipt of such information.


<PAGE>



      (10) The undersigned represent and warrant that they are legal
representatives of, and have the authority to execute this Agreement on behalf
of their respective parties. In the case of COHERENT, this Agreement shall be
valid and binding only if it is signed by an Officer of COHERENT.

PHOTOGEN, INC.                                   COHERENT, INC.

By:   /S/ ERIC WACHTER                           By:   /S/ SCOTT MILLER
     ---------------------------------               ---------------------------
Title:  VICE PRESIDENT AND SECRETARY             Title: SR VP
       -------------------------------                  ------------------------
Date:   18 JAN 2000                              Date:    1-19-00
      --------------------------------                 -------------------------