A conductively cooled, optically face-pumped slab laser comprises a slab laser host 1 having transparent, thermally conductive pump lamp housings 2 bonded to its pump faces. Flashlamps 3 are embedded in pump lamp housings 2 for generating pumplight which is transmitted through the housings 2 into laser host 1 to cause lasing. Heat flow within the laser host 1 is substantially bi-directional, thereby minimizing optically harmful thermal distortion of the host. The apparatus can function as laser amplifier, laser oscillator or combined oscillator/amplifier.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an optically pumped, conductively cooled 
solid-state slab laser having transparent, thermally conductive solid pump 
lamp housings bonded to the pumped faces of the slab for bi-directional 
cooling of the lasing medium by conduction. 
2. Description of the Prior Art 
U.S. Pat. No. 4,734,913 to Morris et al. discloses a unitary solid state 
laser having a solid transparent housing with two cavities. A laser medium 
is embedded in one cavity and a pump lamp in the other. The housing 
completely surrounds the laser medium, so that cooling of the medium by 
the housing is omnidirectional. 
Fluid cooled slab lasers are disclosed, for example, in U.S. Pat. Nos. 
4,800,569 to Azad, 4,734,917 to Johnson, 4,468,774 to Robbins and 
3,665,335 to Tomiyasu. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a conductively cooled, optically 
face-pumped slab laser apparatus comprises, in combination, (a) an 
elongated slab of active laser host having two opposite ends and a pair of 
parallel, optically plane faces extending along its length for receiving 
radiation for optical pumping of the host, and for acting as total 
internal reflective surfaces for creating internal optical paths; (b) 
first and second transparent, thermally conductive solid pump lamp 
housings, each having an optically plane face which is dimensioned to 
match and is bonded to an optically plane face of said laser host by means 
of a bonding agent, which bonding agent has a refractive index which is 
smaller than the refractive index of the laser host, said pump lamp 
housings having at least one cavity extending substantially parallel to 
said optically plane face for receiving pump lamps, said pump lamps 
housing further having a reflective coating for substantially preventing 
escape of the pump light from the housing except at the optically plane 
face which is bonded to said laser host; and (c) pump lamps embedded in 
the cavities of said pump lamp housings for exciting the laser host. 
The laser apparatus of the present invention may function as a laser 
oscillator, a laser amplifier or a combined oscillator/amplifier. In the 
event the laser apparatus is to function as a laser oscillator, it will be 
provided with reflectors adjacent to the opposite ends of the laser host 
to define an optical resonant cavity to support coherent radiation emitted 
by the laser host, optionally along with multi-plexed amplifier passes. 
Preferably, the laser host is alexandrite, emerald or Nd:YAG. The 
transparent, thermally conductive solid pump lamp housings are preferably 
sapphire. Desirably, the sides of the slab which are not bonded to the 
transparent, thermally conductive housings are thermally insulated from 
the surroundings. 
In the conductively cooled, solid-state slab laser of the presently claimed 
construction, conductive cooling is essentially bi-directional, so that 
thermal gradients in the slab are predominantly contained in the plane 
formed by the slab and the pump lamps. This provides laser beam 
compensation for thermal lensing and distortion using the zigzag optical 
path. By the term "pump lamps embedded in the cavity of said pump lamp 
housing" we mean that the pump lamps, such as a flashlamp, are 
substantially surrounded by the housing on all sides, except possibly for 
the ends. Optionally, a pump lamp envelope and the pump lamp housing may 
be integrally formed, with the envelope so formed being provided with an 
optically plane face which is bonded to a pumped face of the laser host. 
Further, either one or both of the pump lamp housings may optionally be 
provided with heat exchange means, such as internal passages for passing 
heat exchange fluid therethrough, external cooling fins, and the like. By 
such means it is possible to control the temperature of the apparatus in 
operation within desired limits, for purposes such as preventing damage 
due to overheating, or for operation within temperature ranges of optimal 
laser host performance, while at the same time maintaining the 
bi-directional heat flow within the lasing medium, with its attendant 
benefits. 
Bonding between housing and slab may conveniently be effected using a 
bonding agent, particularly a thermally fusable bonding agent having high 
optical transmission in the pump region, such as glass frit. 
The pump lamp may be any of the means commonly employed for exciting 
solid-state laser hosts, such as flashlamps. Flashlamps having a 
cerium-doped fused quartz envelope, such as those supplied by Heraeus 
Amersil under the designation M-382, are preferred. Optionally, a suitable 
filter material may be positioned between the pump means and the laser 
host for filtering out undesirable wavelength components generated by the 
pump means.

DETAILED DESCRIPTION OF THE INVENTION 
With reference to FIG. 1, the conductively cooled solid-state slab laser 
apparatus of the present invention comprises a slab laser host 1 having 
two opposites ends and a pair of parallel optically plane faces extending 
along its length. To the parallel, optically plane faces are bonded pump 
lamp housings 2 having a longitudinal bore parallel to the optically plane 
face of the slab laser host 1 Embedded in the bores of pump lamp housings 
2 are a pair of pump lamps 3. The pump lamps 3 serve to excite the laser 
host 1 by providing light for optical pumping of laser host 1. As 
illustrated in FIGS. 1 and 2, pump lamp housings 2 may optionally be 
formed in sections 2a and 2b, which can be separated for easy insertion of 
the pump lamps 3. 
FIG. 2 is a longitudinal cross-sectional view of the apparatus illustrated 
in FIG. 1. The pump lamps are illustrated by flashlamps 3 having 
electrodes 10. Pump lamp housings 2 are bonded to slab laser host 1 by 
means of bonding layer 6. Bonding layer 6 must have a refractive index 
that is smaller than the refractive index of the slab laser host, so that 
the total internal reflective bounces are greater than the critical angle, 
thereby providing that the optically plane faces extending along the 
length of slab laser host 1 act as total internal reflective surfaces for 
creating optical paths within the slab. Conveniently, the bonding agent 
(usually glass) which will form the bonding layer 6 is provided as a 
powder (frit). The bonding agent is positioned between the optically plane 
faces of the slab laser host 1 and pump lamp housing 2, followed by 
heating under clamping pressure to effect thermal fusion of the bonding 
agent and bonding of the mating surfaces. A convenient form of glass 
powder bonding agent is commercially available in the form of tape 
comprising glass powder held together by a binder; the binder evaporates 
or is destroyed in the thermal fusion step. Bonding agents further should 
have high optical transmission in the spectral region of interest, and 
relatively good match of thermal expansion coefficient. In addition, the 
bonding agent should have a melting point that is low enough that the 
agent can be melted (and solidified) without damaging the laser host or 
the pump lamp housing Also, the bonding agent should not deteriorate 
during exposure to the heat and radiation generated by the lamp. Low 
melting glasses, certain polymers such as silicon elastomers and other 
similar materials well known in the art are suitable bonding agents. Care 
should be taken in bonding the slab laser host to the pump lamp housing to 
avoid introduction of bubbles or other inhomogeneities. 
FIG. 3 is a transverse cross-sectional view of apparatus of the type 
illustrated by FIG. 1 showing the slab laser host 1 to which there are 
bonded pump lamp housings 2 which are formed as sections 2a and 2b. Pump 
lamps 3 having electrodes 10 are embedded in pump lamp housings 2. Between 
slab laser host 1 and pump lamp housings 2 a bonding layer 6 is provided. 
In addition, the free sides of slab laser host 1 are thermally insulated 
from the surrounding environment by means of insulating strips 5. The 
insulating strips 5 aid in providing bi-directional conductive heat flow 
from laser host 1 to pump lamp housings 2 in the plane formed by the slab 
and the flashlamps, to thereby provide laser beam compensation for thermal 
lensing and distortion of the laser host 1. Pump lamp housings 2 are 
further provided with a reflective coating 4. Reflective coating 4 
substantially prevents escape of pump lamp light from the housing except 
at the optically plane face which is bonded to the laser host (and except 
possibly at the ends, if uncoated), thereby greatly enhancing the 
efficiency of utilization of the pump light. Silver or gold are preferred 
reflector media. In addition, depending on the emission characteristics of 
the pump lamp and the absorption characteristics of the laser host, it may 
be advantageous that the pump lamp envelope have a filter coating (not 
shown) to eliminate unwanted spectral components of the lamp output. A 
suitably chosen coating will reflect back into the lamp those wavelengths 
(infrared and ultraviolet, for example) that do not efficiently excite the 
laser rod. Furthermore, elimination of the ultraviolet component can 
prevent solarization of the laser rod. Alternatively, especially if the 
laser host is alexandrite, the pump lamp may be provided with an envelope 
having a cerium-doped fused quartz envelope, which perform comparable to 
coated flashlamps carrying UV and IR reflective coatings. Such lamps are 
commercially available. Optionally, the pump lamp envelope may be bonded 
to the bore of pump lamp housing 2. This, however, will not ordinarily be 
desirable because of resultant difficulties in replacing the pump lamp. 
FIG. 4 is a transverse cross-sectional view of laser apparatus of the type 
illustrated in FIG. 1, except that pump lamp housings 2 are not formed 
sectionally so that pump lamps 3 having electrodes 10 must be inserted 
into the bore by sliding them into the bore. Otherwise, the apparatus of 
FIG. 4 is identical to that illustrated in FIG. 3. 
FIG. 5 is a further transverse cross-sectional view of such apparatus 
wherein the lamp envelope and pump lamp housing are integrally formed as a 
unit. Lamp envelope 9 is provided with an optically plane face extending 
along its length which is bonded by means of bonding agent 6 to slab laser 
host 1. 
The conductively cooled slab laser apparatus of the present invention may 
be operated as a laser amplifier, as a laser oscillator, as well as a 
combined laser amplifier/oscillator. In the event it is to be used as a 
laser amplifier, reflecting means for establishing a lasing cavity for 
oscillation need not be provided. However, in the event that the apparatus 
is to be used as a laser oscillator, as schematically illustrated in FIG. 
6, it will be necessary to provide reflecting means for defining a lasing 
cavity, as is illustrated in FIG. 6, by providing a total reflector 7 and 
a partial reflector 8 at opposite ends of slab laser host 1. 
The laser host may be any solid material capable of supporting lasing 
action. Illustrative materials include alexandrite, emerald, Nd:YAG, 
Nd:BEL, Ti-Sapphire, and the like. Since during operation the laser host, 
pump lamp housing and pump lamp all heat up, it is preferred to utilize 
laser media, like alexandrite and emerald, whose output efficiency is not 
diminished at elevated temperatures. 
An important criterion for the choice of material of construction for the 
pump lamp housing is that it transmits in the wavelength region of the 
laser pump bands. Typical of materials that are suitable are certain 
glasses, fused silica, quartz, chrysoberyl and sapphire. Sapphire and 
fused silica are preferred, because they are suitable and readily 
available commercially. Sapphire is a preferred housing material because 
of its superior thermal shock resistance. Glass moldings are also 
suitable. The relevant parameters that guide the choice of materials in a 
particular instance, e.g., transmission spectra, thermal conductivity, 
thermal expansion coefficients and index of refraction are tabulated in 
reference works, such as The American Institute of Physics Handbook, 
published by McGraw-Hill. 
Since various changes may be made in the invention without departing from 
its spirit and essential characteristics it is intended that all matter 
contained in the description shall be interpreted as a illustrative only 
and not in a limiting sense, the scope of the invention being defined by 
the appended claims.