<PAGE>

                                                                     EXHIBIT 3.1

                     RESTATED CERTIFICATE OF INCORPORATION

                                      OF

                               THERMA-WAVE, INC.


                                  ARTICLE ONE

          The name of the Corporation is Therma-Wave, Inc.


                                  ARTICLE TWO

          The address of the Corporation's registered office in the State of
Delaware is 1209 Orange Street, in the City of Wilmington, County of New Castle,
19801.  The name of the registered agent at such address is The Corporation
Trust Company.


                                 ARTICLE THREE

          The nature of the business or purposes to be conducted or promoted is
to engage in any lawful act or activity for which corporations may be organized
under the General Corporation Law of the State of Delaware.


                                 ARTICLE FOUR

                             A.  AUTHORIZED SHARES
                                 -----------------

          The total number of share of capital stock which the Corporation has
authority to issue is 27,000 hares, consisting of:

          (1)  1,000,000 shares of Series A Convertible Preferred Stock, par
               value $.01 per share ("Series A Preferred")';
                                      ------------------

          (2)  20,000,000 shares of Class A Common Stock, par value $.01 per
               share ("Class A Common");
                       --------------

          (3)  4,000,000 shares of Class B Common Stock, par value $.01 per
               share ("Class B Common"); and
                       --------------

          (4)  2,000,000 shares of Class L Common Stock, par value $.01 per
               share ("Class L Common").
                       --------------

                                       1
<PAGE>

The Class A Common, Class B Common and Class L Common, and any other common
stock issued hereafter, are referred to collectively as the "Common Shares."
                                                             -------------
The Series A Preferred and the Common Shares shall have the rights, preferences
and limitations set forth below.  Capitalized terms used but not otherwise
defined in Part A or Part B or Part C of this Article IV are defined in Part D.

                             B.  SERIES A PREFERRED
                                 ------------------

          Section 1.  Dividends.
                      ---------

          1A.  General Obligation.  When and as declared by the Corporation's
               ------------------
Board of Directors and to the extent permitted under the General Corporation Law
of Delaware, the Corporation shall pay preferential dividends in cash to the
holders of the Series A Preferred (the "Series A Preferred") as provided in this
                                        ------------------
Section 1.  Dividends on each share of the Series A Preferred (a "Share") shall
                                                                  -----
be cumulative and accrue at the rate of 6% per annum of the sum of the
Liquidation Value thereof plus all accumulated and unpaid dividends thereon from
and including the date of issuance of such Share to and including the first to
occur of (i) the date on which the Liquidation Value of such Share (plus all
accrued and unpaid dividends thereon) is paid to the holder thereof in
connection with the liquidation of the Corporation or the redemption of such
Share by the Corporation, (ii) the date on which such Share is converted into
shares of Conversion Stock hereunder or (iii) the date on which such shares is
otherwise acquired by the Corporation.  Such dividends shall accrue whether or
not they have been declared and whether or not there are profits, surplus or
other funds of the Corporation legally available for the payment of dividends.
The date on which the Corporation initially issues any Shares shall be deemed to
be its "date of issuance" regardless of the number of times transfer of such
Share is made on the stock records maintained by or for the Corporation and
regardless of the number of certificates which may be issued to evidence such
Share.

          1B.  Dividend Reference Dates.  To the extent not paid on May 16 of
               ------------------------
each year, beginning May 16, 1998 (the "Dividend Reference Date"), all dividends
                                        -----------------------
which have accrued on each Share outstanding during the year ending upon each
such Dividend Reference Date shall be accumulated and shall remain accumulated
dividends with respect to such Share until paid to the holder thereof.

          1C.  Distribution of Partial Dividend Payments.  Except as otherwise
               -----------------------------------------
provided herein, if at any time the Corporation pays less than the total amount
of dividends then accrued with respect to the Series A Preferred, such payment
shall be distributed pro rata among the holders thereof based upon the number of
Shares held by each such holder.

          Section 2.  Liquidation.  Upon any liquidation, dissolution or winding
                      -----------
up of the Corporation (whether voluntary or involuntary), each holder of Series
A Preferred shall be entitled to be paid, before any distribution or payment is
made upon any Junior Securities, an amount in cash equal to the greater of (a)
the aggregate Liquidation Value

                                       2
<PAGE>

of all Shares held by such holder (plus all accrued and unpaid dividends
thereon, which for all purposes hereof shall include dividends which have
accrued since the last Dividend Reference Date) and (b) the amount that such
holder would have received had such holder converted such Shares into shares of
Class A Common immediately prior to such liquidation, dissolution or winding up,
and the holders of Series A Preferred shall not be entitled to any further
payment. If upon any such liquidation, dissolution or winding up of the
Corporation the Corporation's assets to be distributed among the holders of the
Series A Preferred are insufficient to permit payment to such holders of the
aggregate amount which they are entitled to be paid under this Section 2, then
the entire assets available to be distributed to the Corporation's stockholders
shall be distributed pro rata among such holders based upon the aggregate
Liquidation Value (plus all accrued and unpaid dividends) of the Series A
Preferred held by each such holder. Not less than 30 days prior to the payment
date stated therein, the Corporation shall mail written notice of any such
liquidation, dissolution or winding up to each record holder of Series A
Preferred, setting forth in reasonable detail the amount of proceeds to be paid
with respect to each Share and each share of Common Stock in connection with
such liquidation, dissolution or winding up.

          Section 3.  Priority of Series A Preferred on Dividends and
                      -----------------------------------------------
Redemptions.  So long as any Series A Preferred remains outstanding, without the
-----------
prior written consent of the holders of a majority of the outstanding shares of
Series A Preferred, the Corporation shall not, nor shall it permit any
Subsidiary to, redeem, purchase or otherwise acquire directly or indirectly any
Junior Securities, nor shall the Corporation directly or indirectly pay or
declare any dividend or make any distribution upon any Junior Securities;
provided that the Corporation may repurchase shares of Common Stock from former
employees of the Corporation and its Subsidiaries to the extent permitted by the
Corporation's agreements related to the Corporation's indebtedness, including
without limitation any indenture, whether entered into in connection with
transactions contemplated by the Recapitalization Agreement or thereafter, and
including any extensions of refinancing thereof.

          Section 4.  Redemptions.
                      -----------

          4A.  Scheduled Redemption.  On May 17, 2004 (the "Scheduled Redemption
               --------------------                         --------------------
Date "), the Corporation shall redeem all outstanding Shares of Series A
----
Preferred at a price per Share equal to the Liquidation Value thereof (plus
accrued and unpaid dividends thereof).

          4B.  Optional Redemptions.  The Corporation may, at any time and from
               --------------------
time to time after the first to occur of (i) June 30, 1998 and (ii) the
Corporation's initial Public Offering, redeem all or any portion of the Shares
of Series A Preferred then outstanding at a price per Share equal to the
Liquidation Value thereof (plus all accrued and unpaid dividends thereon).  Any
partial redemption pursuant to this paragraph shall be for a number of Shares,
the aggregate Liquidation Value of which, together with accrued and unpaid
dividends thereon, is at least $5,000,000, and redemptions made

                                       3
<PAGE>

pursuant to this paragraph shall not relieve the Corporation of its obligation
to redeem Shares on the Scheduled Redemption Dates.

          4C.  Redemption Payments.  For each Share which is to be redeemed
               -------------------
hereunder, the Corporation shall be obligated on the Redemption Date to pay to
the holder thereof (upon surrender by such holder at the Corporation's principal
office of the certificate representing such Share) an amount in cash equal to
the Liquidation Value of such Share (plus all accrued and unpaid dividends
thereon).  If the funds of the Corporation legally available for redemption of
Shares on any Redemption Date are insufficient to redeem the total number of
Shares to be redeemed on such date, those funds which are legally available
shall be used to redeem the maximum possible number of Shares pro rata among the
holders of the Shares to be redeemed based upon the aggregate Liquidation Value
of such Shares held by each such holder (plus all accrued and unpaid dividends
thereon).  At any time thereafter when additional funds of the Corporation are
legally available for the redemption of Shares, such funds shall immediately be
used to redeem the balance of the Shares which the Corporation has become
obligated to redeem on any Redemption Date  but which it has not redeemed.

          4D.  Notice of Redemption.  Except as otherwise provided herein, the
               --------------------
Corporation shall mail written notice of each redemption of any Series A
Preferred (other than a redemption at the request of a holder or holders of
Series A Preferred) to each record holder thereof not more than 60 nor less than
30 days prior to the date on which such redemption is to be made.  In case fewer
than the total number of Shares represented by any certificate are redeemed, a
new certificate representing the number of unredeemed Shares shall be issued to
the holder thereof without cost to such holder within five business days after
surrender of the certificate representing the redeemed Shares.

          4E.  Determination of the Number of Each Holder's Shares to be
               ---------------------------------------------------------
Redeemed.  The number of Shares of Series A Preferred to be redeemed from each
--------
holder thereof in redemptions hereunder shall be the number of Shares determined
by multiplying the total number of Shares to be redeemed times a fraction, the
numerator of which shall be the total number of Shares then held by such holder
and the denominator of which shall be the total number of Shares then
outstanding.

          4F.  Dividends After Redemption Date.  No Share shall be entitled to
               -------------------------------
any dividends accruing after the date on which the Liquidation Value of such
Share (plus all accrued and unpaid dividends thereon) is paid to the holder of
such Share.  On such date, all rights of the holder of such Share shall cease,
and such Share shall no longer be deemed to be issued and outstanding.

          4G.  Redeemed or Otherwise Acquired Shares.  Any Shares which are
               -------------------------------------
redeemed or otherwise acquired by the Corporation shall be canceled and retired
to authorized but unissued shares and shall not be reissued, sold or
transferred.

                                       4
<PAGE>

          4H.  Special Redemptions.
               -------------------

               (i)   If, in connection with or after any Public Offering, any
member of the Bain Group receives any proceeds in respect of Common Stock owned
by such member, the Corporation shall give prompt written notice to the holders
of the Series A Preferred of such event. The holder or holders of a majority of
the Series A Preferred then outstanding may require the Corporation to redeem
all outstanding shares of Series A Preferred at a price per Share equal to the
Liquidation Value thereof (plus all accrued and unpaid dividends thereon) by
giving written notice to the Corporation of such election within 30 days after
the receipt of such notice from the Corporation. Upon receipt of such election,
the Corporation shall be obligated to redeem the outstanding Shares of Series A
Preferred on a date fixed by the Corporation, which date shall be not more than
30 days after the Corporation's receipt of such notice.

               (ii)  If a Change in Ownership has occurred or the Corporation
obtains knowledge that a Change in Ownership is proposed to occur, the
Corporation shall give prompt written notice of such Change in Ownership
describing in reasonable detail the material terms and date of consummation
thereof to each holder of Series A Preferred. The holder or holders of a
majority of the Series A Preferred then outstanding may require the Corporation
to redeem all outstanding shares of Series A Preferred at a price per Share
equal to the Liquidation Value thereof (plus all accrued and unpaid dividends
thereon) by giving written notice to the Corporation of such election prior to
the later of (a) 30 days after receipt of the Corporations notice and (b) five
days prior to the consummation of the Change in Ownership (the "Expiration
                                                                ----------
Date").
----

          Upon receipt of such election, the Corporation shall be obligated to
redeem the outstanding Shares of Series A Preferred on the later of (a) the
occurrence of the Change in Ownership or (b) five days after the Corporations
receipt of such election(s). If any proposed Change in Ownership does not occur,
all requests for redemption in connection therewith shall be automatically
rescinded.

          The term "Change in Ownership" means any sale or transfer or series of
                    -------------------
sales or transfers by the Bain Group (other than to any Affiliate of any member
of the Bain Group) of at least 25% of the Common Stock purchased by the Bain
Group pursuant to the Recapitalization Agreement, determined on the basis of the
cost of such Common Stock

               (iii) If a Fundamental Change is proposed to occur, the
Corporation shall give written notice of such Fundamental Change describing in
reasonable detail the material terms and date of consummation thereof to each
holder of Series A Preferred not more than 45 days nor less than 20 days prior
to the consummation of such Fundamental Change, and the Corporation shall give
each holder of Series A Preferred prompt written notice of any material change
in the terms or timing of such transaction. The holder or holders of a majority
of the Series A Preferred then outstanding may require the Corporation to redeem
all outstanding Shares of Series A Preferred at a price per Share equal to the
Liquidation Value thereof (plus all accrued and unpaid dividends thereon) by
giving written notice to the Corporation of such election

                                       5
<PAGE>

prior to the later of (a) five days prior to the consummation of the Fundamental
Change or (b) 30 days alter receipt of notice from the Corporation.

          Upon receipt of such election, the Corporation shall be obligated to
redeem the outstanding Shares of Series A Preferred upon the consummation of
such Fundamental Change. If any proposed Fundamental Change does not occur, all
requests for redemption in connection therewith shall be automatically
rescinded.


          The term "Fundamental Change" means any sale or transfer of all or
                    ------------------
substantially all of the assets of the Corporation and its Subsidiaries on a
consolidated basis in any transaction or series of related transactions.

               (iv)  Redemptions made pursuant to this paragraph 4H shall not
relieve the Corporation of its obligation to redeem Series A Preferred on the
Scheduled Redemption Dates pursuant to paragraph 4A above.

          4I.  Partial Redemptions.  Notwithstanding anything contained herein,
               -------------------
any redemption by the Corporation of less then all of the Shares of Series A
Preferred then held by each holder must be a number of Shares of Series A
Preferred sufficient, in the good faith opinion of counsel to the holder, to not
be treated as a dividend under Section 302 of the Internal Revenue Code of 1986,
as amended (or any comparable successor provision), as to such holder.

          - Section 5.  Voting Rights.  The holders of the Series A Preferred
                        -------------
shall be entitled to notice of all stockholders meetings in accordance with the
Corporations bylaws, and the holders of the Series A Preferred shall be entitled
to vote on all matters submitted to the stockholders for a vote together with
the holders of the Common Stock voting together as a single class with each
share of Common Stock entitled to one vote per share and each Share of Series A
Preferred entitled to one vote for each share of Common Stock issuable upon
conversion of the Series A Preferred as of the record date for such vote or, if
no record date is specified, as of the date of such vote.

          Section 6.  Conversion.
                      ----------

          6A.  Conversion Procedure.
               ---------- ---------

               (i)  At any time, any holder of Series A Preferred may convert
all of the Series A Preferred held by such holder into shares of Conversion
Stock. Each Share of Series A Preferred shall be convertible into one share of
Conversion Stock (as such amount is adjusted for stock splits, stock dividends,
recapitalizations and similar transactions).

               (ii) Except as otherwise provided herein, each conversion of
Series A Preferred shall be deemed to have been effected as of the close of
business on the date on which the certificate or certificates representing the
Series A Preferred to be

                                       6
<PAGE>

converted have been surrendered for conversion at the principal office of the
Corporation. At the time any such conversion has been effected, the rights of
the holder of the Shares converted as a holder of Series A Preferred (including
the right to receive accrued and unpaid dividends on the Series A Preferred)
shall ease and the Person or Persons in whose name or names any certificate or
certificates for shares of Conversion Stock are to be issued upon such
conversion shall be deemed to have become the holder or holders of record of the
shares of Conversion Stock represented thereby.

               (iii) The conversion rights of any Share subject to redemption
hereunder shall terminate on the Redemption Date for such Share unless the
Corporation has failed to pay to the holder thereof the Liquidation Value of
such Share (plus all accrued and unpaid dividends thereon).

               (iv)  Notwithstanding any other provision hereof, if a conversion
of Series A Preferred is to be made in connection with a Public Offering, a
Change in Ownership, a Fundamental Change or other transaction affecting the
Corporation, the conversion of any Shares of Series A Preferred may, at the
election of the holder thereof, be conditioned upon the consummation of such
transaction, in which case such conversion shall not be deemed to be effective
until such transaction has been consummated.

               (v)   As soon as possible after a conversion has been effected,
the Corporation shall deliver to the converting holder a certificate or
certificates representing the number of shares of Conversion Stock issuable by
reason of such conversion in such name or names and such denomination or
denominations as the converting holder has specified.

               (vi)  The issuance of certificates for shares of Conversion Stock
upon conversion of Series A Preferred shall be made without charge to the
holders of such Series A Preferred for any issuance tax in respect thereof or
other cost incurred by the Corporation in connection with such conversion and
the related issuance of shares of Conversion Stock. Upon conversion of each
Share of Series A Preferred, the Corporation shall take all such actions as are
necessary in order to insure that the Conversion Stock issuable with respect to
such conversion shall be validly issued, fully paid and nonassessable, free and
clear of all taxes, liens, charges and encumbrances with respect to the issuance
thereof

               (vii) The Corporation shall not close its books against the
transfer of Series A Preferred or of Conversion Stock issued or issuable upon
conversion of Series A Preferred in any manner which interferes with the timely
conversion of Series A Preferred.  The Corporation shall assist and cooperate
with any holder of Shares required to make any governmental filings or obtain
any governmental approval prior to or in connection with any conversion of
Shares hereunder (including, without limitation, making any filings required to
be made by the Corporation).

                                       7
<PAGE>

               (viii) The Corporation shall at all times reserve and keep
available out of its authorized but unissued shares of Conversion Stock, solely
for the purpose of issuance upon the conversion of the Series A Preferred, such
number of shares of Conversion Stock issuable upon the conversion of all
outstanding Series A Preferred.  All shares of Conversion Stock which are so
issuable shall, when issued, be duly and validly issued, fully paid and
nonassessable and free from all taxes, liens and charges.  The Corporation shall
take all such actions as may be necessary to assure that all such shares of
Conversion Stock may be so issued without violation of any applicable law or
governmental regulation or any requirements of any domestic securities exchange
upon which shares of Conversion Stock may be listed (except for official notice
of issuance which shall be immediately delivered by the Corporation upon each
such issuance).  The Corporation shall not take any action which would cause the
number of authorized but unissued shares of Conversion Stock to be less than the
number of such shares required to be reserved hereunder for issuance upon
conversion of the Series A Preferred.

          6B.  Notices.  The Corporation shall give written notice to all
               -------
holders of Series A Preferred at least 20 days prior to the date on which the
Corporation closes its books or takes a record (a) with respect to any dividend
or distribution upon Common Stock, (b) with respect to any pro rata subscription
offer to holders of Common Stock or (c) for determining rights to vote with
respect to any dissolution or liquidation.

          Section 7.  Reorganization, Reclassification, Consolidation, Merger or
                      ----------------------------------------------------------
Sale.  Any recapitalization, reorganization, reclassification, consolidation,
----
merger, sale of all or substantially all of the Corporations assets or other
transaction, in each case which is effected in such a manner that the holders of
Common Stock are entitled to receive (either directly or upon subsequent
liquidation) stock, securities or assets with respect to or in exchange for
Common Stock is referred to herein as an "Organic Change."  Prior to the
consummation of any Organic Change, the Corporation shall make appropriate
provisions to insure that each of the holders of Series A Preferred shall
thereafter have the right to acquire and receive, in lieu of or in addition to
(as the case may be) the shares of Conversion Stock immediately theretofore
acquirable and receivable upon the conversion of such holder's Series A
Preferred, such shares of stock, securities or assets as such holder would have
received in connection with such Organic Change if such holder had converted its
Series A Preferred immediately prior to such Organic Change.

          Section 8.  Registration of Transfer.  The Corporation shall keep at
                      ------------------------
its principal office a register for the registration of Series A Preferred.
Upon the surrender of any certificate representing Series A Preferred at such
place, the Corporation shall, at the request of the record holder of such
certificate, execute and deliver (at the Corporation's expense) a new
certificate or certificates in exchange therefor representing in the aggregate
the number of Shares represented by the surrendered certificate. Each such new
certificate shall be registered in such name and shall represent such number of
Shares as is requested by the holder of the surrendered certificate and shall be
substantially identical in form to the surrendered certificate, and dividends
shall accrue on the Series A Preferred represented by such new certificate from
the date to which

                                       8
<PAGE>

dividends have been fully paid on such Series A Preferred represented by the
surrendered certificate.

          Section 9.   Replacement.  Upon receipt of evidence reasonably
                       -----------
satisfactory to the Corporation (an affidavit of the registered holder shall be
satisfactory) of the ownership and the loss, theft, destruction or mutilation of
any certificate evidencing Shares of Series A Preferred, and in the case of any
such loss, theft or destruction, upon receipt of indemnity reasonably
satisfactory to the Corporation (provided that if the holder is a financial
institution or other institutional investor or an original party to the
Recapitalization Agreement its own agreement shall be satisfactory), or, in the
case of any such mutilation upon surrender of such certificate, the Corporation
shall (at its expense) execute and deliver in lieu of such certificate a new
certificate of like kind representing the number of Shares of such class
represented by such lost stolen, destroyed or mutilated certificate and dated
the date of such lost, stolen, destroyed or mutilated certificate, and dividends
shall accrue on the Series A Preferred represented by such new certificate from
the date to which dividends have been fully paid on such lost, stolen, destroyed
or mutilated certificate.

          Section 10.  Amendment and Waiver.  No amendment, modification or
                       --------------------
waiver shall be binding or effective with respect to any provision of Sections 1
to 11 of this Part B without the prior written consent of the holders of a
majority of the Series A Preferred outstanding at the time such action is taken;
provided that no change in the terms hereof may be accomplished by merger or
consolidation of the Corporation with another corporation or entity unless the
Corporation has obtained the prior written consent of the holders of a majority
of the Series A Preferred then outstanding.

          Section 11.  Notices.  Except as otherwise expressly provided
                       -------
hereunder, all notices referred to herein shall be in writing and shall be
delivered by registered or certified mail, return receipt requested and postage
prepaid, or by reputable overnight courier service, charges prepaid, and shall
be deemed to have been given when so mailed or sent (i) to the Corporation, at
its principal executive offices and (ii) to any stockholder, at such holder's
address as it appears in the stock records of the Corporation (unless otherwise
indicated by any such holder).

                               C.  COMMON SHARES
                                   -------------

          Except as otherwise provided in this Part C or as otherwise required
by applicable law, all Common Shares shall be identical in all respects and
shall entitle the holders thereof to the same rights and privileges, subject to
the same qualifications, limitations and restrictions.

          Section 1.   Voting Rights.  Except as otherwise required by
                       -------------
applicable law, all holders of Class A Common and Class L Common shall be
entitled to one vote per share on all matters to be voted on by the
Corporation's stockholders. Except as otherwise provided by applicable law, all
holders of Class B Common shall have no right to vote on any matters to be voted
on by the Corporations stockholders.

                                       9
<PAGE>

          Section 2.  Distributions.  At the time of each Distribution, such
                      -------------
Distribution shall be made to the holders of Common Shares in the following
priority:

               (i)   The holders of Class L Common, as a separate class, shall
be entitled to receive all or a portion of such Distribution (ratably among such
holders based upon the aggregate Unpaid Yield on Class L Common held by each
such holder as of the time of such Distribution) equal to the aggregate Unpaid
Yield on the outstanding shares of Class L Common as of the time of such
Distribution, and no Distribution or any portion thereof shall be made under
paragraph 2(ii) or (iii) below until the entire amount of the Unpaid Yield on
the outstanding shares of Class L Common as of the time of such Distribution has
been paid in full. The Distributions made pursuant to this paragraph 2(i) to
holders of Class L Common shall constitute a payment of Yield on Class L Common.

               (ii)  After the required amount of a Distribution has been made
in full pursuant to paragraph 2(i) above, the holders of Class L Common, as a
separate class, shall be entitled to receive all or a portion of such
Distribution (ratably among such holders based upon the aggregate Unreturned
Cost of shares of Class L Common held by each such holder as of the time of such
Distribution) equal to the aggregate Unreturned Cost of the outstanding shares
of Class L Common as of the time of such Distribution, and no Distribution or
any portion thereof shall be made under paragraph 2(iii) below until the entire
amount of the Unreturned Cost of the outstanding shares of Class L Common as of
the time of such Distribution has been paid in full. The Distributions made
pursuant to this paragraph 2(ii) to holders of Class L Common shall constitute a
payment of Cost of Class L Common.

               (iii) After the required amount of a Distribution has been made
pursuant to paragraphs 2(i) and 2(ii) above, holders of Common Shares, as a
group, shall be entitled to receive the remaining portion of such Distribution
(ratably among such holders based upon the number of Common Shares held by each
such holder as of the time of such Distribution).

          Section 3.  Stock Splits and Stock Dividends.  The Corporation shall
                      --------------------------------
not in any manner subdivide (by stock split, stock dividend or otherwise) or
combine (by stock split, stock dividend or otherwise) the outstanding Common
Shares of one class unless the outstanding Common Shares of all the other
classes shall be proportionately subdivided or combined, respectively.  All such
subdivisions and combinations shall be payable only in Class L Common to the
holder of Class L Common, in Class A Common to the holders of Class A Common,
and in Class B Common to the holders of Class B Common.  In no event shall a
stock split or stock dividend constitute a payment of Yield or a return of Cost.

          Section 4.  Conversion of Class L Common Upon Initial Public Offering.
                      ---------------------------------------------------------

               (i)   Upon the consummation of the Corporations initial Public
Offering, each outstanding share of Class L Common shall, without any action by
the

                                       10
<PAGE>

holder thereof, automatically convert into a number of shares of Class A Common
equal to the sum of (i) one and (ii) the result of (x) the Unreturned Cost plus
Unpaid Yield of such share of Class L Common divided by (y) the price per share
of the Class A Common in the Public Offering (in each case before giving effect
to any stock split declared in connection with such Public Offering).

               (ii)  As soon as possible after a conversion has been effected,
the Corporation shall deliver to the converting holder a certificate or
certificates representing the number of shares of Class A Common issuable by
reason of such conversion in such name or names and such denomination or
denominations as the converting holder has specified.

               (iii) The issuance of certificates for shares of Class A Common
upon conversion of Class L Common shall be made without charge to the holders of
such Class L Common for any issuance tax in respect thereof or other cost
incurred by the Corporation in connection with such conversion and the related
issuance of shares of Class A Common.  Upon conversion of each share of Class L
Common, the Corporation shall take all such actions as are necessary in order to
insure that the Class A Common issuable with respect to such conversion shall be
validly issued, fully paid and nonassessable, free and clear of all taxes,
liens, charges and encumbrances with respect to the issuance thereof.

               (iv)  The Corporation shall not close its books against the
transfer of Class L Common or of Class A Common issued or issuable upon
conversion of Class L Common in any manner which interferes with the timely
conversion of Class L Common. The Corporation shall assist and cooperate with
any holder of shares required to make any governmental filings or obtain any
governmental approval prior to or in connection with any conversion of shares
hereunder (including, without limitation, making any filings required to be made
by the Corporation).

               (v)   The Corporation shall at all times reserve and keep
available out of its authorized but unissued shares of Class A Common, solely
for the purpose of issuance upon the conversion of the Class L Common, such
number of shares of Class A Common issuable upon the conversion of all
outstanding Class L Common. All shares of Class A Common which are so issuable
shall, when issued, be duly and validly issued, fully paid and nonassessable and
free from all taxes, liens and charges. The Corporation shall take all such
actions as may be necessary to assure that all such shares of Class A Common may
be so issued without violation of any applicable law or governmental regulation
or any requirements of any domestic securities exchange upon which shares of
Class A Common may be listed (except for official notice of issuance which shall
be immediately delivered by the Corporation upon each such issuance). The
Corporation shall not take any action which would cause the number of authorized
but unissued shares of Class A Common to be less than the number of such shares
required to be reserved hereunder for issuance upon conversion of the Class L
Common.

                                       11
<PAGE>

          Section 5.  Conversion of Class B Common.
                      ----------------------------

               (i)   Upon consummation of the Corporations initial Public
Offering, each holder of Class B Common shall be entitled to convert any or all
of the shares of such holder's Class B Common into the same number of shares of
Class A Common.

               (ii)  Each conversion of shares of Class B Common into shares of
Class A Common shall be effected by the surrender of the certificate or
certificates representing the shares to be converted at the principal office of
the Corporation at any time during normal business hours, together with a
written notice by the holder of such Class B Common stating that such holder
desires to convert the shares, or a stated number of shares, of Class B Common
represented by such certificate or certificates into Class A Common. Each
conversion shall be deemed to have been effected as of the close of business on
the date on which such certificate or certificates have been surrendered and
such notice has been received, and at such time the rights of the holder of the
converted Class B Common as such holder shall cease and the person or persons in
whose name or names the certificate or certificates for shares of Class A Common
are to be issued upon such conversion shall be deemed to have become the holder
or holders of record of the shares of Class A Common represented thereby.

               (iii) Promptly after the surrender of certificates and the
receipt of such written notice, the Corporation shall issue and deliver in
accordance with the surrendering holder's instructions (a) the certificate or
certificates for the Class A Common issuable upon such conversion and (b) a
certificate representing any Class B Common which was represented by the
certificate or certificates delivered to the Corporation in connection with such
conversion but which was not converted.

               (iv)  The issuance of certificates for Class A Common upon
conversion of Class B Common shall be made without charge to the holders of such
shares for any issuance tax in respect thereof or other cost incurred by the
Corporation in connection with such conversion and the related issuance of Class
A Common. All shares of Class A Common which are so issuable shall, when issued,
be duly and validly issued, fully paid and nonassessable and free from all
taxes, liens and charges.

               (v)   The Corporation shall at all times reserve and keep
available out of its authorized but unissued shares of Class A Common, solely
for the purpose of issuance upon the conversion of Class B Common, such number
of shares of Class A Common issuable upon the conversion of all outstanding
Class B Common. All shares of Class A Common which are so issuable shall, when
issued, be duly and validly issued, fully paid and nonassessable and free from
all taxes, liens and charges.

               (vi)  The Corporation shall not close its books against the
transfer of Class A Common or of Class B Common issued or issuable upon
conversion of Class A Common in any manner which would interfere with the timely
conversion of Class A Common.

                                       12
<PAGE>

               (vii) If the Corporation in any manner subdivides or combines the
outstanding shares of Class A Common or Class B Common, as the case may be, the
outstanding shares of the Class A Common (in the case of a subdivision or
combination of the Class B Common) or the Class B Common (in the case of a
subdivision or combination of the Class A Common), shall be proportionately
subdivided or combined in a similar manner.

          Section 6.  Registration or Transfer.  The Corporation shall keep at
                      ------------------------
its principal office (or such other place as the Corporation reasonably
designates) a register for the registration of Common Shares.  Upon the
surrender of any certificate representing shares of any class of Common Shares
at such place, the Corporation shall, at the request of the registered holder of
such certificate, execute and deliver a new certificate or certificates in
exchange therefor representing in the aggregate the number of shares of such
class represented by the surrendered certificate, and the Corporation forthwith
shall cancel such surrendered certificate.  Each such new certificate will be
registered in such name and will represent such number of shares of such class
as is requested by the holder of the surrendered certificate and shall be
substantially identical in form to the surrendered certificate. The issuance of
new certificates shall be made without charge to the holders of the surrendered
certificates for any issuance tax with respect thereof or other cost incurred by
the Corporation in connection with such issuance.

          Section 7.  Replacement.  Upon receipt of evidence reasonably
                      -----------
satisfactory to the Corporation (an affidavit of the registered holder will be
satisfactory) of the ownership and the loss, theft, destruction or mutilation of
any certificate evidencing one or more shares of any class of Common Shares, and
in the case of any such loss, theft or destruction, upon receipt of indemnity
reasonably satisfactory to the Corporation (provided that if the holder is a
financial institution or other institutional investor or an original party to
the Recapitalization Agreement, its own agreement will be satisfactory), or, in
the case of any such mutilation upon surrender of such certificate, the
Corporation shall (at its expense) execute and deliver in lieu of such
certificate a new certificate of like kind representing the number of shares of
such class represented by such lost, stolen, destroyed or mutilated certificate
and dated the date of such lost, stolen, destroyed or mutilated certificate.

          Section 8.  Notices.  All notices referred to herein shall be in
                      -------
writing, shall be delivered personally or by first class mail, postage prepaid,
and shall be deemed to have been given when so delivered or mailed to the
Corporation at its principal executive offices and to any stockholder at such
holder's address as it appears in the stock records of the Corporation (unless
otherwise specified in a written notice to the Corporation by such holder).

          Section 9.  Fractional Shares.  In no event will holders of fractional
                      -----------------
shares be required to accept any consideration in exchange for such shares other
than consideration which all holders of Common Stock are required to accept.

                                       13
<PAGE>

          Section 10.  Amendment and Waiver.  No amendment or waiver of any
                       --------------------
provision of Part C of this Article IV shall be effective without the prior
written consent of the holders of a majority of the then outstanding Common
Shares voting as a single class; provided that no amendment as to any terms or
provisions of, or for the benefit of, any class of Common Shares that adversely
affects the powers, preferences or special rights of such class of Common Shares
shall be effective without the prior consent of the holders of a majority of the
then outstanding shares of such affected class of Common Shares, voting as a
single class.

                                D.  DEFINITIONS
                                    -----------

          "Affiliate" means, with respect to any Person, any other Person,
           ---------
entity or investment fund controlling, controlled by or under common control
with such Person and, in the case of a Person which is a partnership, any
partner of such Person.

          "Bain Group" means, collectively, Bain Capital Fund V, L.P., Bain
           ----------
Capital Fund V--B, L.P., BCIP Associates, BCIP Trust Associates, L.P., and
Randolph Street Partners.

          "Change in Ownership" has the meaning set forth in paragraph 4H of
           -------------------
Part B hereof.

          "Common Stock" means, collectively, the Corporations Class A Common
           ------------
Stock, the Corporation's Class B Common Stock, the Corporation's Class L Common
Stock and any other class of capital stock of the Corporation hereafter
authorized which is not limited to a fixed sum or percentage of par or stated
value in respect to the rights of the holders thereof to participate in
dividends or in the distribution of assets upon any liquidation, dissolution or
winding up of the Corporation, other than the Series A Preferred.

          "Conversion Stock" means shares of the Corporations Class A Common
           ---------- -----
Stock, par value $.01 per share; provided that if there is a change such that
the securities issuable upon conversion of the Series A Preferred are issued by
an entity other than the Corporation or there is a change in the type or class
of securities so issuable, then the term "Conversion Stock" shall mean the
securities issuable upon conversion of the Series A Preferred.

          "Cost" of each share of Class L Common shall be equal to $19.085 per
           ----
share (as proportionally adjusted for all stock splits, stock dividends and
other recapitalizations affecting the Class L Common).

          "Distribution" means each distribution made by the Corporation to
           ------------
holders of Common Shares, whether in cash, property, or securities of the
Corporation and whether by dividend, liquidating distributions or otherwise;
provided that neither of the following shall be a Distribution, (a) any
redemption or repurchase by the Corporation of any Common Shares for any reason
or (b) any recapitalization or exchange of any

                                       14
<PAGE>

Common Shares, or any subdivision (by stock split, stock dividend or otherwise)
or any combination (by stock split, stock dividend or otherwise) of any
outstanding Common Shares.

          "Fundamental Change" has the meaning set forth in paragraph 4H of Part
           ------------------
B hereof.

          "General Corporation Law" means the General Corporation Law of the
           -----------------------
State of Delaware, as amended from time to time.

          "Junior Securities" means any capital stock or other equity securities
           -----------------
of the Corporation, except for the Series A Preferred.

          "Liquidation Value" of any Share of Series A Preferred as of any
           -----------------
particular date shall be equal to $18.40.

          "Person" means an individual, a partnership, a corporation, a limited
           ------
liability company, an association, a joint stock company, a trust, a joint
venture, an unincorporated organization and a governmental entity or any
department, agency or political subdivision thereof.

          "Public Offering" means any offering by the Corporation of its capital
           ---------------
stock or equity securities to the public pursuant to an effective registration
statement under the Securities Act of 1933, as then in effect, or any comparable
statement under any similar federal statute then in force; provided that for
purposes of paragraph 4H of Part B hereof, a Public Offering shall not include
an offering made in connection with a business acquisition or combination or an
employee benefit plan.

          "Recapitalization Agreement" means the Recapitalization Agreement
           --------------------------
dated as of December 18, 1996 among the Corporation, the Bain Group, Toray
Industries, Inc., Toray Industries (America), Inc. and Shimadzu Corporation.

          "Redemption Date" as to any Share means the date specified in the
           ---------------
notice of any redemption at the Corporations option or at the holder's option or
the applicable date specified herein in the case of any other redemption;
provided that no such date shall be a Redemption Date unless the Liquidation
Value of such Share (plus all accrued and unpaid dividends thereon and any
required premium with respect thereto) is actually paid in full on such date,
and if not so paid in full, the Redemption Date shall be the date on which such
amount is fully paid.

          "Subsidiary" means any corporation of which a majority of the shares
           ----------
of outstanding capital stock possessing the voting power (under ordinary
circumstances) in electing the board of directors are, at the time as of which
any determination is being made, owned by the Corporation either directly or
indirectly through Subsidiaries.

          "Unpaid Yield" of any share of Class L Common means an amount equal to
           ------------
the excess, if any, of (a) the aggregate Yield accrued on such share, over (b)
the

                                       15
<PAGE>

aggregate amount of Distributions made by the Corporation that constitute
payment of Yield on such share.

          "Unreturned Cost" of any share of Class L Common means an amount equal
           ---------------
to the excess, if any, of (a) the Cost of such share, over (b) the aggregate
amount of Distributions made by the Corporation that constitute a return of the
Cost of such share.

          "Yield" means, with respect to each outstanding share of Class L
           -----
Common for each calendar year, the amount accruing on such share each day during
such year at the rate of 12% per annum of the sum of (a) such shares Unreturned
Cost, plus (b) Unpaid Yield thereon for all prior years.  In calculating the
amount of any Distribution to be made to the Class L Common during a calendar
year, the portion of a Class L Common share's Yield for such portion of such
year elapsing before such Distribution is made shall be taken into account.

                                  ARTICLE FIVE

          The Corporation is to have perpetual existence.

                                  ARTICLE SIX

          In furtherance and not in limitation of the powers conferred by state,
the board of directors of the Corporation is expressly authorized to make, alter
or repeal the by-laws of the Corporation.

                                 ARTICLE SEVEN

          Meetings of stockholders may be held within or without the State of
Delaware, as the by-laws of the Corporation may provide.  The books of the
Corporation may be kept outside the State of Delaware at such place or places as
may be designated from time to time by the board of directors or in the by-laws
of the Corporation.  Election of directors need not be by written ballot unless
the by-laws of the Corporation so provide.

                                 ARTICLE EIGHT

          To the fullest extent permitted by the General Corporation Law of the
State of Delaware as the same exists or may hereafter be amended, a director of
this Corporation shall not be liable to the Corporation or its stockholders for
monetary damages for a breach of fiduciary duty as a director. Any repeal or
modification of this ARTICLE EIGHT shall not adversely affect any right or
protection of a director of the Corporation existing at the time of such repeal
or modification.

                                  ARTICLE NINE

          The Corporation expressly elects not to be governed by (S)203 of the
General Corporation Law of the State of Delaware.

                                       16
<PAGE>

                                  ARTICLE TEN

          The Corporation reserves the right to amend, alter, change or repeal
any provision contained in this certificate of incorporation in the manner now
or hereafter prescribed herein and by the laws of the State of Delaware, and all
rights conferred upon stockholders herein are granted subject to this
reservation.

                                       17