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                                                                   EXHIBIT 10.41

UNITED STATES PATENT   [19]                 [11]  PATENT NUMBER:       5,507,739

VASSILIADIS ET AL.                          [45]  DATE OF PATENT:  APR. 16, 1996

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[54]    DENTAL LASER

[75]    Inventors:  ARTHUR VASSILIADIS, Mountain View; 
                    DAVID R. HENNINGS, Newcastle; JOSEPH
                    W. SCHAFFER, Mountain View; DAVID J.
                    FULLMER, Foster City; MICHAEL H.
                    BREWER, Felton, all of Calif.; TERRY D.
                    MYERS, Bloomfield Hills; WILLIAM D.
                    MYERS, Birmingham, both of Mich.

[73]    Assignee:   AMERICAN DENTAL TECHNOLOGIES, INC.,
                    Southfield, Mich.

[21]    Appl. No.:  898,730

[22]    Filed:      JUN. 15, 1992

                    (Under 37 CFR 1.47)

[51]    INT. CL.(6) ............................  A61B 17/36
[52]    U.S. CL. .......................606/3; 602/2; 607/89;
                                                      372/23
[58]    FIELD OF SEARCH .....................606/2, 3, 10-19;
                                           607/89; 372/21-23

[56]                     REFERENCES CITED
                         
                      U.S. PATENT DOCUMENTS

        4,757,507   6/1988 Wondrazek..................372/23
        4,791,927  12/1988 Menger......................606/3
        4,940,411   7/1990 Vassiliadis et al. .........606/3
        5,009,658   4/1991 Damgaard-Iversen et al. ....606/3
        5,066,291  11/1991 Stewart ....................606/3
        5,125,922   6/1992 Dwyer ......................606/2

Primary Examiner - Stephen C. Pellegrino
Assistant Examiner - M. Peffley
Attorney, Agent, or Firm - Gifford, Krass, Groh, Sprinkle, Patmore, Anderson &
Citkowski

[57]                            ABSTRACT

A duel wavelength laser is disclosed for use in dental therapeutic
applications.  The dual wavelength laser includes a laser cavity in which a
laser crystal is disposed and preferably the laser crystal if an Nd:YAG laser,
which, upon excitation, lases at two different wavelengths, each of which has a
different gain.  A shutter, or alternatively an optical filter, is selectively
disposed within the optical path of the laser crystal whereupon the higher gain
wavelength is selectively suppressed.  Thus, with the shutter or optical filter
removed from the optical path, the laser lases at its higher gain wavelength. 
Conversely, with the shutter or filter positioned within the optical path, the
higher gain wavelength is effectively suppressed so that the laser crystal
lases at the lower gain wavelength.

                          6 CLAIMS, 1 DRAWING SHEET


                             [SCHEMATIC DRAWING]



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U.S. PATENT                      APR. 16, 1996                         5,507,739


                             [SCHEMATIC DRAWING]

                                   FIG - 1


                             [SCHEMATIC DRAWING]


                                   FIG - 2
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                                  5,507,739

                                      1

                                 DENTAL LASER

                         BACKGROUND OF THE INVENTION


        1.  Field of the Invention
        The present invention relates generally to lasers and, more
particularly, to a dual wavelength laser for use in dental therapeutic
applications.

        2.  Description of the Prior Art
        There are a number of previously known lasers that are used in dental
applications.  One such laser is a neodymium doped yttrium aluminum garnet
laser (Nd:YAG) which, when excited, produces a pulsed output used for dental
therapeutic applications.  These dental therapeutic applications include, for
example, the cutting and eradication of soft tissue, desensitization of teeth,
endontic procedures and other dental procedures.

        For an Nd:YAG laser crystal, as well as other laser crystals, the
wavelength of the emission is a function of the stimulated emission section and
thus the gain of the laser crystal.  For an Nd:YAG laser, the highest gain
wavelength is 1.06 microns so that, upon excitation, the Nd:YAG laser crystal
will normally lase at its highest gain wavelength and thus at 1.06 microns.

        The Nd:YAG laser, however, when excited, can also lase at different
wavelengths, such as 1.32, 0.96 and 1.44 microns.  All of these other
wavelengths, however, have a higher lasing threshold, and thus lower gain, than
the 1.06 wavelength so that normally the Nd:YAG laser, once excited, lases at
its maximum gain wavelength, i.e. 1.06 microns.

        For many dental therapeutic applications, the 1.06 micron wavelength of
the Nd:YAG laser has proven superior to the other, lower gain wavelengths of
the Nd:YAG laser.  In other applications, especially the cutting of soft
tissue, however, the Nd:YAG laser operated at 1.32 microns has proven superior
to the 1.06 microns wavelength due to the higher water absorption at 1.32
microns versus 1.06 microns.

        Consequently, it would be desirable to have two lasers in the dental
office, i.e. one laser which lases at 1.06 microns and a second laser which
lases at 1.32 microns.  Such a situation, however, is very costly due to the
high cost of each laser.

                       SUMMARY OF THE PRESENT INVENTION

        The present invention overcomes the above mentioned disadvantages of
the previously known dental lasers by providing a single laser which can be
selectively excited to lase at either 1.06 or 1.32 microns.

        In brief, the dental therapeutic laser of the present invention
comprises a laser cavity in which an elongated laser crystal is disposed. 
Preferably, the laser crystal is a neodymium doped yttrium aluminum garnet
crystal (Nd:YAG).

        Conventional means, such as a flash lamp, are then used to excite the
crystal so that the crystal lases at two wavelengths.  Means are then provided
for selectively suppressing the higher gain 1.06 microns wavelength so that the
laser continues to lase at its next lower gain wavelength of 1.32 microns.

        In one form of the invention, a three mirror resonator with a shutter
assembly is employed to selectively obtain laser operation at either 1.06 or
1.32 microns.  In the three mirror resonator, one mirror is positioned in
alignment with one end of the laser crystal which reflects between 10% and 98%
of the laser emission at both 1.06 and 1.32 microns.

        A pair of axially spaced mirrors are then positioned adjacent the
opposite end of the laser rod.  The first mirror, i.e. the mirror closest to
the laser rod is coated with a material which produces high reflection of laser
emission at 1.32 microns and, simultaneously, is highly transmissive at 1.06
microns.  Thus, laser emission at 1.32 microns is normally reflected by the
first mirror back toward the laser rod while the laser emission at 1.06 microns
passes through the first mirror.

        The second mirror is highly reflective of laser emissions at 1.06
microns.  In addition, an optical shutter is selectively disposed between the
two mirrors.  

        With the shutter positioned in between the mirrors, the shutter
effectively suppresses the laser emission at the higher gain 1.06 wavelength
whereupon laser operation at 1.32 microns will continue.  Conversely, with the
shutter removed from the optical path, the 1.06 microns wavelength laser
emission will be effectively reflected by the second mirror so that, due to the
higher gain of the 1.06 wavelength, laser emission will continue at the 1.06
wavelength.

        In a second embodiment of the invention, a partial reflector is
positioned in the optical path adjacent one end of the laser rod while a single
mirror is positioned in the optical path at the opposite end of the laser rod. 
This single mirror, furthermore, is highly reflective of laser emission at both
1.06 microns and 1.32 microns.

        An optical filter is then selectively disposed in the optical path
between the end of the laser rod and the mirror.  This optical filter includes
a coating which is highly absorbent of laser emission at 1.06 microns and,
conversely, highly transmissive of laser emission at 1.32 microns.  Thus, with
the optical filter removed from the optical path, laser emission proceeds at
the dominant or high gain 1.06 microns wavelength.  Conversely, with the
optical filter positioned within the optical path, the higher gain 1.06 microns
wavelength laser emission is effectively suppressed while simultaneously
permitting resonance at the lower gain 1.32 microns wavelength.

        Any conventional means, such as a solenoid assembly, can be used to
selectively position either the shutter or the filter within the optical path.

                       BRIEF DESCRIPTION OF THE DRAWING

        A better understanding of the present invention will be had upon
reference to the following detailed description, when read in conjunction with
the accompanying drawings, wherein like reference characters refer to like
parts throughout the several views, and in which:

        FIG. 1 is a longitudinal partial diagrammatic view illustrating a first
preferred embodiment of the present invention and illustrating the laser
operation at a lower gain wavelength; and

        FIG. 2 is a longitudinal sectional view similar to FIG. 1, but showing
a second preferred embodiment of the present invention.

                      DETAILED DESCRIPTION OF PREFERRED
                          EMBODIMENTS OF THE PRESENT
                                  INVENTION

        With reference first to FIG. 1, a first preferred embodiment of the
present invention is thereshown and comprises an elongated laser rod or crystal
10 disposed in a laser cavity.

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                                  5,507,739


                                      3

A conventional flash lamp 12 is used to excite or stimulate the laser rod 10
into laser emission.

        The laser rod 10 is preferably a neodymium doped yttrium aluminum
garnet (Nd:YAG) laser which, when excited, lases at a number of different
wavelengths, namely 0.96, 1.06, 1.32 and 1.44 microns.  However, of all these
wavelengths, the stimulated emission cross section, and thus the gain, of the
1.06 wavelength is many times greater than the emission cross section at the
other wavelengths.  Similarly, laser emission at 1.32 microns enjoys the second
highest stimulated emission cross section and thus the second highest gain
after the 1.06 microns wavelength.

        A partial reflector 14 is positioned within the optical path 16 of the
laser rod 10.  This partial reflector 14 reflects between 10% and 98% of the
laser emission from the rod 10 at both 1.06 and 1.32 microns.  Consequently, a
portion of the laser emission impinging upon the partial reflector 14 passes
through the reflector 14, as shown at 18, and forms the laser emission from the
laser cavity.

        Still referring to FIG. 1, a first mirror 20 is positioned within the
optical path 16 of the laser rod 10 adjacent the opposite end 22 of the rod 10. 
A coating is provided on one side 24 of the mirror 20 which is highly
reflective at 1.32 microns and preferably has a reflectance of about 99.5% at
1.32 microns.  Simultaneously, the coating on the side 24 of the mirror 20 is
highly transmissive to laser radiation at 1.06 microns and preferably transmits
more than 95% of laser emission at 1.06 microns.  The opposite side 26 of the
mirror 20 is also highly transmissive of laser radiation at 1.06 microns.

        A second mirror 28 is also positioned within the optical path 16 of the
laser rod 10 at a position spaced outwardly from the mirror 20.  One side 29 of
the mirror 28 is highly reflective of laser radiation at 1.06 microns as well
as other wavelengths.

        Still referring to FIG. 1, an optical shutter 30 is selectively moved
between a position within the optical path 16, as shown in solid line, and to
a position outside of the optical path 16, as shown in phantom line, by a
solenoid assembly 32.  This optical shutter 30 is constructed of a material
which is highly absorbent, and thus non-reflective and non-transmissive of
laser emission.  Preferably, the shutter 30 is constructed of an opaque
material, such as aluminum.

        The operation of the FIG. 1 embodiment will now be described.  With the
shutter 30 positioned in the optical path as shown in solid line in FIG. 1, the
laser rod 10 is excited by the flash lamp 12.  Once excited, the laser rod 10
emits laser radiation at a number of different frequencies, including 1.06
microns and 1.32 microns.  The partial reflector 14 and first mirror 20 form a
resonator for the laser at 1.32 microns due to the high reflectivity of the
mirror 20 at 1.32 microns.  Simultaneously, the laser emission at the higher
gain wavelength of 1.06 microns passes through the first mirror and is absorbed
by the opaque shutter 30.  Since the higher gain 1.06 micron laser emission is
suppressed by the shutter 30, laser emission at 1.32 microns wavelength is
emitted from the laser cavity as shown at 18.

        Conversely, with the shutter 30 moved to the position shown in phantom
line, the second mirror 28 and partial reflector form a resonator for the
higher gain laser emission at 1.06 microns.  Since the gain of the laser
emission at 1.06 microns is many fold the gain of the emission at 1.32 microns,
the laser emission will continue at 1.06 microns along the optical path 18 from
the laser cavity.

        With reference now to FIG. 2, a second embodiment of the present
invention is thereshown.  In the second embodiment, a flash lamp or other
excitation means 12 is used to excite the laser rod 10 which, as before, is an
Nd:YAG laser crystal.  The partial reflector 14 is also positioned in the
optical path 16 adjacent one end of the laser rod 10.

        Unlike the FIG. 1 embodiment, however, a single mirror 40 is provided
in the optical path 16 of the laser rod 10 adjacent its end 22.  This mirror 40
includes a surface 42 which is highly reflective at both 1.06 microns and 1.32
microns.  

        An optical filter 44 is selectively moved by a solenoid mechanism 46,
or other electromechanical means, between a position shown in solid line in
which the filter 44 is positioned within the optical path 16 between the end 22
of the laser rod 10 and the mirror 40, and a position shown in phantom line in
which the optical filter 44 is removed from the optical path 16.  The filter 44
is constructed of a material which has high absorption of laser emission at
1.06 microns but which is also highly transmissive of laser emission at 1.32
microns.  
        
        Preferably, the optical filter 44 is constructed of a thin material,
such as yttrium iron garnet, and is anti-reflection coated on both of its sides
for both wavelengths 1.06 microns and 1.32 microns.

        In operation, with the filter 44 positioned within the optical path 16
(solid line in FIG. 2) the optical filter 44 effectively absorbs and thus
suppresses the higher gain laser emission at 1.06 microns.  Simultaneously, the
reflector 14 and mirror 40 form a resonator for the lower gain laser emission
at 1.32 microns.

        Conversely, with the filter 44 moved to its second position removed
from the optical path 16 (phantom line in FIG. 2) the mirror 40 and partial
reflector 14 form a resonator for the laser emission at the higher gain 1.06
microns wavelength.

        Alternatively, a thin dichroic mirror which reflects at 1.06, but
transmits at 1.32 microns can replace the filter 44.

        From the foregoing, it can be seen that the present invention provides
a simple and yet highly effective laser assembly for dental uses in which a
single laser rod can be selectively excited to lase at either 1.06 microns      
or 1.32 microns wavelengths.  This thus allows greater flexibility in
selection of the appropriate wavelengths for the desired dental therapeutic
application.

        The present invention can also be used to obtain dual or even multiple
wavelength laser operation for lasers other than Nd:YAG lasers.  For example, a
holmium doped YAG laser lases at both 2.1 microns and 3.9 microns.  Selective
suppression of either wavelength will allow operation of the other wavelength.

        Similarly, an erbium doped YAG laser lases at 1.65 microns, 2.3 microns
and 2.9 microns.  By selectively suppressing two of the wavelengths, laser
operation continues at the third wavelength.

        Having described our invention, however, many modifications thereto
will become apparent to those skilled in the art to which it pertains without
deviation from the spirit of the invention as defined by the scope of the
appended claims.  

        We claim:

        1.  A laser for use in dental therapeutic applications comprising:

            a laser cavity,

            a laser crystal, said crystal being disposed in said cavity and 
               capable of lasing at two different wavelengths, 

            means for exciting said crystal so that said crystal lases at said 
               two wavelengths,

            means for selectively suppressing one of said wavelengths so that 
               said crystal continues to lase at the other of two wavelengths 
               wherein said laser crystal is elongated and emits laser 
               radiation out each end, a partial reflector positioned in
               alignment with one end of said crystal and wherein said 
               suppressing means comprises a first and second mirror being 
               positioned in alignment with the


<PAGE>   5
                                  5,507,739



                                      5

            other end of said laser crystal, said first mirror being spaced
            from said second end of said crystal by a distance which is
            resonant with said first wavelength, said second mirror being
            spaced from said second end of said crystal by a distance which is
            resonant with said second wavelength, said first mirror being
            substantially transparent to said second wavelength, an optically
            opaque shutter and means for selectively positioning said shutter
            between said first and second mirrors.

        2.  The invention as defined in claim 1 wherein said laser crystal 
comprises a neodymium doped yttrium aluminum garnet crystal.

        3.  The invention as defined in claim 2 wherein one wavelength 
comprises 1.06 microns and the other wavelength comprises 1.32 microns.

        4.  The invention as defined in claim 1 and comprising a coating on 
said first mirror which is highly reflective at said first wavelength and highly
transmissive at said second wavelength.

        5.  The invention as defined in claim 1 and comprising a coating on said
reflector which is partially reflective at both wavelengths.

        6.  The invention as defined in claim 1 wherein said positioning means
comprises a solenoid.

                                  * * * * *



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                  UNITED STATES PATENT AND TRADEMARK OFFICE
                          CERTIFICATE OF CORRECTION

PATENT NO.  :    5,507,739
DATED       :    April 16, 1996
INVENTOR(S) :    Vassiliadis et al.

    It is certified that error appears in the above-identified patent and
    that said Letters Patent is hereby corrected as shown below:


Column 1, line 21, after "emission", insert --cross--











[SEAL]                                           SIGNED AND SEALED THIS

                                          SEVENTEENTH DAY OF SEPTEMBER, 1996


        Attest:                                     Bruce Lehman


        Mary Green
                                                    BRUCE LEHMAN
        Attesting Officer

                                          Commissioner of Patents and Trademarks