The general form of these multi-segment rod type
MULTIPLE HOST FACE-PUMPED LASER lasers as shown in U.S. Pat. No. 3,715,682 issued to
Young have glass discs which are generally edge
RELATED APPLICATIONS pumped and therefore have some radial thermal gradi
This application is a continuation-in-part of Ser. No. 5 ents due,to "°n-uniform pumping. These radial gradi
317,134 filed Nov. 2, 1981, now abandoned. e"ts result In degradat>on of the, >>eam coherence. Opt.
cal compensation can be introduced as shown m U.S.
BACKGROUND OF THE INVENTION Pat. No. 3,675,152 issued to Young. The radial refrac
1. Field of the Invention ln tive index Sradien/ compensation means^ utilized re
This invention relates to a face pumped laser, and 10 fires ll!at therma equilibrium be reached before the
, , „ , , .,. ■ , j laser pulse has full energy and good coherence. An
more particularly, to such a laser providing in one head u *\. . . &j e>
i r. r i u * ii ■ . i r alternative optical compensation means is the multi
a plurality of laser hosts allowing a greater volume of *\ . 're _ . XT , . , .
, Y. . . „ . , path array as shown in U.S. Pat. No. 3,628,179 issued to
host material and therefore higher average power laser . . c .'
. . .., . . . . .5 , r.° c r Cuff et al. This compensates for transverse temperature
output while maintaining the benefits of the face J- » J * i.n *
. 4 t i • ^ in*- i . i_ • 15 gradients due to coolant flow but does not compensate
pumped, total internal reflection laser technique. *r ^ ... M t erature dient due „on.
2 Description of the Prior Art uniform p m A„ of the above multiple.segment
It is well known in the art tha laser devices emit rod ( ^ ^ve in common the limitat^n tlfat the
electromagnetic radiation of wavelengths generally in ^ v thro h ^ ... When w
the infrafred and visible portions of the electromagnetic 2Q md ^ tition rates are employedi the
spectrum. The radiation emission is substantially coher- . enfi isB arti^, absorbed b theF coolant. This
ent and is characterized by a narrow wavelength band. ... ... ... and thus index of refraction
Laser devices are operable using a suitable medium or dients which cause serious D tical distortion or loss host m which a population inversion may be established of coherence in the lasin beam_ m a particular metastable energy level by proper optical 25 Present!y face d lasers are advantageously pumping . Neodymium glass ruby, helium, neon, and employed as pulsed lasers. A face pumped laser rmits carbon dioxide are media which . are commonly em- substantially uniform activitation and concomitant heatployed m lasers. By pumping or irradiating the active ing across the ,aser aperature in contract t0 the nonuni. medium with electromagnetic radiation possessing form optical properties of the side-pumped, rod-type power necessary to create the population inversion, J0 laser device u s pat No 3,631,361-Almasi et al., conditions permitting coherent emission may be ob- assigned t0 the same assignee as the present invention, tamed. The means emitting the radiation causing mver- discioses an arrangement for substantially increasing the sion is called "pumping means" while the wavelength of pulse repetition rate of face-pumped laser devices by the radiation is known as the "pumping wavelength". eliminating the distortion due to nonuniform heating.
Laser devices which emit high energy pulses are well 35 xhe losses and the distortion due to the laser output
known in the art as pulsed lasers. The emitted pulses, beam passjng through the interspersed coolant flow
though high in energy, are short in duration, lasting on remain.
the order of milliseconds to picoseconds. The face pumped iaser with total internal reflection The laser output is only a small percentage of the wnen uniformly activated has intrinsic beam wave front input energy, a large percentage of the energy ending 40 compensation for thermal gradients within the laser up as heat in the laser medium. In pulsed lasers, one or nost and no wave front distorition due to laser output more surfaces of the active medium are cooled in order beam paSsage through the coolant. These characteristo extract the excess heat. Because of the limited ther- tjcs are advantageously utilized for high average power, mal conductivity of the host material, the excess heat is high beam intensity and high repetition rate lasers. Exmore rapidly removed from near the surface than from 45 ampies of this art are U.S. Pat. No. 3,633,126 issued to the interior, causing the center of the host to be warmer Martin et al and U.S. Pat. No. 4,214,216 issued to Jones, than the surface. Repeated operation of the laser host, jr., both assigned also to the same assignee as the presprecluding a proper cooling period, causes a substantial ent invention.
thermal gradient to be established, resulting in possible A unique characteristic of the face pumped laser with
strutural failure or distortion of the output beam. Lasers 50 total internal reflection is that the laser beam is directed
employing host materials characterized by low thermal through the laser host by means of total internal reflec
conductivities are particularly limited to low pulse rep- tions from the major faces which also admit the pump
etition rates. ing radiation. Thus maintaining the optical alignment
Recent interest in high repetition rates of pulsed la- and, hence, the performance of a laser resonator that
sers has led to increased activity in this field. Since a 55 incorporates a face pumped laser host with total internal
number of materials, particularly those of the doped reflections is dependent upon maintaining the laser host
glass species, which are employed as the active laser major faces substantial flat and parallel. The potential
host have low thermal conductivity, several approaches means of disturbing the resonator alignment is to cause
have been taken to overcome this restraint on pulse flexure of the laser host by either inadequate support or
repetition rate. These approaches have in common the 60 unequal heating (or cooling) of the major faces. Flexure
segmenting of a side-pumped, rod type laser host and of the laser host curves the major face where the total
interspersing of a flowing coolant. The result of this internal reflection occurs and cause the exiting laser
procedure is that the unwanted heat is more quickly beam to be non-parallel to the entering laser beam. Thus removed through the relatively smaller dimension of all faced pumped lasers with total internal reflections the segmented laser host material and therefore the 65 require proper means of supporting and cooling the composite arrangement can be operated at higher pulse laser host to ensure that there is no flexure of the laser repetition rates without structural failure due to ther- host to cause misalignment that results in degraded
mally induced stress. performance.