Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~ ~6~9~
The present invention relates to laser devices and
more particularly to a Q-swltched laser in integral cartridge
form.
.
; There are two types of lasers, namely those that
operate to produce an output continuously~ and khose thak are
operated to produce a pulsed outpu~, This invention is directed
to the latter type, In Pulsed output lasers~ it is desired to
intermittently produce a sin~le relatively high amplitude pulse
of coherent radiation, It has been found~ howeverJ that many
laslng materials, such as Nd:YAG ruby crystals~ employed in
pulsed output lasers~ tend to produce a series of low amplitude
~; . .
' . .
; ` .
,
- 1 -
. . .
9 0
pulses rather khan the desired single high amplitude output pulse.
The reason for this ls that the lasing rnaterlal begins to produce
. a coherent beam of radiatlon by stimulated emission berore the
inverted populatlon density of the atoms o~ the laslng material
has time to reach a very high magnitude.
In order to prevent a coherent beam of radiation from
being produced ln a pulsed output laser untll sufficient time
has elapsed for the inverted population density of the atoms of
the lasing ~aterial to reach a very high value so that the desired
single high amplitude pulse of coherent radiatlon is generated
rather than an undesired series of low amplitude pulsesJ lt has
been the practice to insert a Q-swltch between one of the reflec-
tive surfaces and the lasing materlal The Q-switch in a first
operating state lowers the effective gain of the laser to a point
below unity so that the above described regenerative chain
~; reaction does not take place Therefore, by maintaining the
Q-s~itch in.its first condition for a time interval sufficient
for the lnverted population density to reach a high value and
then switching the ~-swltch to a second operative condition
~ 20 which effectively disconnects t,he Q-switch and permits the
: gain of the laser to rise above unity~ the above descr~bed
regenerative chain takes place and a single high amplitude pulse
of coherent radiation is produced.
One well known type of Q-switch is a saturable absorber
which operates as an optical absorption filter at the ~asing
~ ~requency only when unsaturated) more particularly, a saturable
: ¦ absorber may be composed of a liquid or solid solution of an
organlc dye or may be gaseous in form In any event, the satur-
able absorber when unsaturated absorbs a sufficient number of
3 photons to ma~ntain the gain of the laser below unity. However~
the active absorbing photons causes the saturable absorber to
ultimately become saturated at which time the optical absorption .
- 2 -
~ ~4~
fllter comes relatlvelD tran~parent, permlttlne the galn of the
laser to rise to a point above ~llty and a single pulse Or
coherent radiation of the predetermined frequency o~ the laser
is produced,
U,S, Patent No, 3,500,2349 entitled) "Unltary Q-swltch
Laser Devlce", P,V~ Goedertier, which lssued on March 10, 1970,
discloses a unitary Q-switch laser device wherein the entire laser
structure with the e~ception of the pumping source is made in
the form of a single unitary structure having only one interface
between materials of different indexes of re~ractionO The device
furthermore includes a rod having one end polished to provide
a spherical mirror surface ~orming one end Or the resonator, a
saturable absorber cell ~ixedly attached to one end at the other
end of the rod, and a flat mirror surface fixedly attached to the
other end of the ~aturable absorber which cooperates with the
spherical mirror surface to form an elliptical cavity therebetween
It is an ob~ect o~ the present invention~ therefore~ to
provide an improvement in Q-switched laser devices.
It is another obJect of the present invention to pro-
vlde an lmproved Q-switched laser cartridge in the form of a
` unitary integrated structure,
It is yet another-ob~ect of the present invention to
provide an improved Q-switched laser cartridge havlng an improved
e~ficiency in reliability while operating in extreme environ-
mental conditions,
~ :: . ~ .
Brie~l~, these and other ob~ects are accomplished by
a small size, light weight and low cost Q-switched laser in
integr,al cartridge-form for battery powered pocket size portable
applicatlons. More partlcularly, the laser cartridge of ~he
- 3 -
. .
~ .
1164991)
sub~ect invention compri~es a laser crystal, a passive Q-switch
~ormed of an optlcal grade plastic~ namely polymethylmethacrylate
impregnated with a saturable absorber dye~ a ~irst reflector
f~xedly connected to the passive Q-switch material with optical
quality adhesive, a second re~lector fixedly attached to the
other end of the laser crys~al wherein the first reflector and
the second re~lector cooperate to form an unstable resonator,
and collimating optics ~ixedly attached to the second reflector
with optical quality adhesive wherein the la~er crystal, the
passive Q-switch and the first and second reflectors as well
as the collimating optics form an integral assembly
Brief Description of the Drawin~
F~gure 1 is a diagrammatic view o~ the pre~erred
; embodiment o~ the lnvention
Descriptlon of the Pre~erred Embodiment
As shown in the drawing, reference numeral 10 desig-
nates a hybrid u~stable resonator laser cartridge according to
the sub~ect invention which is adapted to be located in an
optical pump cavity~ not shown~ utilized, for example J in battery
powered pocket-sized portable military laser applications, a
typical example of which is in a miniature rangefinder.
AccordinglyJ the device 10 is of a relatively small size, e g
; 3 millimeters (mm) by 20 millimeters. It is light in weight and
is adapted to withstand a wide range of temperature and shock
parameters ordinarily found in military environments ~he
cartridge 10 comprises an integrated structure which eliminates
the need for an optical bench to allgn the resonator as well as
eliminates the need to hermetically seal the device. The laser
cartridge accordlng to the subject invention is relatively simple
; 3 in design and comprises a laser gain medium 12 in the rorm o.~ an
elongated Nd:YAG crystal rod having a partially rerlective output
- 4 -
~: 1 ',..
~ .a~4sso
surface 14 whlch acts as a ~lat resonator element and which
operates in con~unction with a convex resonator element 16 having
a reflective sur~ace 18 to rorm a hybrid unstable resonator
configuration. Intermedlate the convex rerlecting sur~ace 18
and the rod 12 is located a passive Q-switch 20 consisting of a
saturable dye impregnated optical grade plastic, preferably
being nickel-complex dyed polymethylmethacrylate (PMMA) whose
optical density is selectively controlled. At the opposite end
of the laser rod adJacent the partially reflective sur~ace 14
is located an optical colllmatlng lens 22 The ~our components
12, 16, 20 and 22 are bonded together ln axlal alignment by an
optical grade adhesive formlng an integrated structure. The
adhesive interfaces are shown by reference numerals 24, 26 and 28.
The adhesive used provides the necessary dimensional stdbility
and strength whlch permi~s the ~olnlng and index matching of
markedly di~erent temperature coe~ficient materials, thereby
permitting expansion and contraction w-lthout bond ~ailure
The plastic Q-switch 20 operates in a well known manner
to saturate and decrease the threshold which increases the Q
Or the cavity when a predetermined inversion has been reached~
thus allowing the formation of a laser output pulse which exits
the collimatlng lens 2'~ While the Q-switch 20 can be molded in
a variety o~ physical shapes and optical densities, it is shown
for purposes o~ illustration as a substa`ntially ~lat component
; This type of Q-switch can be operated without complex driving
electronics and-thus allows the overall equipment to meet low
ostsJ small slze and weight constralnts in a minirange~inder
application, particularly adapted for military use
The resonator configuration o~ the sub~ect invention
3 as shown is a novel version Or a conventional stable resonator;
; - 5 -
'`
,
however, the output beam is transmission coupled instead of the
convent~onal annular coupling, The output bearn in turn is
collimated ~iith a simple plano-convex lens bonded and index
matched to the partially tran~mi~slve outp~t re~lector. The
unstable resonator substantially improves the beam quality Or the
output beam over the multi-mode stable resonator and approaches
the di~fract-10ll limit. The efficiency i also increased by
making use of the available mode volume. Th~s is a direct result
of the much more uniform intensity distribution within the
unstable resonator allowing the passive Q-swltch to bleach to
the limits of the crystal rod diameter.
Another lmportant advantage of the resonator con-
~iguration resulting from the structure-shown is the elimfnation
of hot spots which tend to cause damage of the passive Q-switch
and the adhesive by excessive concentration of energy, The
resulting e~ect is insurance of longer li~e and much improved
reliability.
The laser cartridge o~ the subject invention ls
assembled by ~irst bonding the convex mirror 16 to the plastic
Q-switch 20. The laser rod 12 is next held in place and the
mirror/Q-switch sub-assembly is aligned to ~orm the resonator
and bonded into place, Finallyl the collimating len~ 22 is
bonded to the output sur~ace of the cr~rstal to yield the
integral hybrid unstable resonator laser cartridge 10. Such a
structure combines the desirable features of the large volume
single mode operation and small angular divergence o~ the
unstable resonator with the circular output beam and the more
favorable far field energy distribution o~ the single mode
stable resonator. The reliability ls maximlzed by using a
plastic Q-switch which together wlth the resonator and the
collimating optlcs is bonded to the laser crystal tQ ~orm,an
.
' - 6 -
. .. ..... . . ..
1~64!39~
integral assembly less than O.ll~cm3 in volume.
Having thus shown and descrlbed what is at present
consldered to be the preferred embodiment of the invention, the
same has been made by way of illustration and not limitation
and accordingly all alterations, modifications and changes
coming within the spirit of the appended clai.ms are herein
meant to be included.
