Quanta-Ray, Inc.

Leland Stanford Junior University

Richard L Herbst

Robert L Byer

Robert L Mortensen

Stephen J Brosnan

William A Bell

In a high power laser, such as one employing a relatively high gain lasing medium such as CO.sub.2 or Nd:YAG, the optical resonator for the laser comprises a positive branch unstable resonator. The output beam is coupled from the unstable resonator by means of a partially transmissive mirror of the resonator, whereby a filled-in beam is obtained while facilitating optical alignment of the output coupling means. In a preferred embodiment, the optical resonator comprises a pair of mirrors collinearly arranged on the optical axis of the resonator to supply an output beam which is collinear with the optical axis of the resonator. The filled-in output beam is of generally uniform power density across the transverse cross sectional dimensions thereof, whereby a near diffraction limited output beam is obtained with more uniform power density.

Laser employing an unstable resonator having an output transmissive

The high power laser includes a high gain medium (&gt;80%) such as a lightly doped Nd:YAG rod contained within an unstable optical resonator of the type wherein power flows outward from the optical axis of the resonator. The output beam is coupled out of the resonator by means of a coupling device having a high coupling factor (&gt;55% of the circulating power inside the optical resonator) and in a preferred embodiment the coupling factor is as high as 80-90%. The optical resonator is preferably a confocal resonator employing one concave mirror and one convex mirror. The convex mirror forms the output coupling device for providing a high degree of diffraction output coupling around the periphery of the output mirror. The output beam is collimated in the region of the output mirror. The curvatures of the two mirrors forming the optical resonator are dimensioned to take into account the positive focusing lens effect of the high gain medium produced by a transverse thermal gradient in the high gain medium encountered in use when pumped by flash lamps. The laser is Q-switched by means of a linear polarizer and a pulsed KD*P quarter wave plate. The output beam has 25 megawatts of peak power with a pulse width of 10 nanoseconds, a pulse repetition rate of 10 pulses per second. The output beam has a power density of 75 megawatts per square centimeter.

High power laser employing an unstable resonator

In a transversely pumped dye laser, such as a laser oscillator or laser amplifier, the optical pumping radiation is directed into the dye laser gain medium with the angle of divergence of the Poynting vector of the pumping wave radiation being not less than 45.degree. and preferably 90.degree. from the Poynting vector, or its reciprocal, of the optical wave radiation being amplified within the dye laser gain medium, whereby transverse pumping is obtained. In addition, the optical pumping wave radiation is directed into the dye laser gain medium with the angular divergence of the polarization of the electric vector of the pumping wave radiation being not greater than 45.degree., and preferably parallel to the polarization of the electric vector, or the reciprocal thereof, of the optical wave radiation which is being amplified by the dye laser gain medium, whereby the efficiency of conversion of pump energy into amplified optical wave energy is enhanced. In a preferred embodiment, the pump beam is directed generally parallel to and spaced from the output beam of the dye laser oscillator. A dye laser amplifier cell is disposed between the two beams and pump energy is directed through the amplifier cell generally in the opposite direction to that of the dye oscillator beam and approximately colinear therewith for longitudinal pumping in the amplifier.

Transversely pumped dye laser having improved conversion efficiency

A tunable source of infrared radiation is obtained by irradiating an assemblage of Raman active gaseous atoms or molecules with a high intensity pumping beam of coherent radiation at a pump frequency .omega..sub.p to stimulate the generation of Stokes wave energy at a Stokes frequency .omega..sub.s and to stimulate the Raman resonant mode at the Raman mode frequency .omega..sub.R within the irradiated assemblage where the pump frequency .omega..sub.p minus the Stokes frequency .omega..sub.s is equal to the Raman mode frequency .omega..sub.R. The stimulated assemblage is irradiated with a tunable source of coherent radiation at a frequency .omega..sub.i to generate the output infrared radiation of the frequency .omega..sub.0 which is related to the Raman mode frequency .omega..sub.R and the input wave .omega..sub.i by the relation .omega..sub.0 =.omega..sub.i .+-..omega..sub.R. In one embodiment the interaction between the pump wave energy .omega..sub.p and the tunable input wave energy .omega..sub.i is collinear and the ratio of the phase velocity mismatch factor .DELTA.k to the electric field exponential gain coefficient T is within the range of 0.1 to 5. In another embodiment the pump wave energy .omega..sub.p and the tunable input wave energy .omega..sub.i have velocity vectors k.sub.p and k.sub.i which cross at an angle to each other to compensate for phase velocity mismatches in the medium. In another embodiment, the Stokes wave energy .omega..sub.s is generated by pump energy .omega..sub.p in a first Raman cell and .omega..sub.s, .omega..sub.i and .omega..sub.p are combined in a second Raman mixing cell to produce the output at .omega..sub.i.

Tunable infrared source employing Raman mixing

Output coherent infrared radiation is obtained in a continuously tunable band from 1.4 microns to 25 microns and longer wavelengths. The 1.06 micron output of a Nd:YAG laser, or a harmonic thereof, is difference mixed in a nonlinear crystal, as of LiIO.sub.3 or LiNbO.sub.3 with a synchronously pumped output of a tunable dye laser oscillator to produce a first tunable output over the range of 0.7 micron to 5.0 microns. The output of the crystal mixer is amplified or difference mixed in a second nonlinear crystal mixer with the 1.06 pump output to produce an output tunable over the range of 1.4 microns to 25 microns and longer wavelengths. Suitable second crystal mixers comprise LiNbO.sub.3 for the range of 1.4 to 4.4 microns and operable as an amplifier in the range of 1.4 microns to 2.1 microns, and as a difference mixer in the range of 2.1 to 4.4 microns, AgGaS.sub.2 in the range of 4 microns to 12 microns and operating as a difference mixer, and CdSe operating as a difference mixer for the range of 12 microns to 25 microns.

Continuously tunable wideband coherent infrared source

A high power single mode laser is disclosed which includes a Q-switch for switching the laser on in two stages: firstly, to a relatively high loss level just above threshold where it is held to permit a train of relaxation oscillator spikes to be established and then it is switched to a second stage in which the Q-switch is in a lossless state to allow the resonant mode within the laser to build up to maximum power. An optical detector monitors the resonant optical radiation level within the optical resonator and produces an output signal for each of the relaxation spikes. A trigger circuit, responsive to the detected oscillator spikes, triggers the Q-switch so as to switch it to the second or lossless state upon receipt of the second or any other subsequent relaxation oscillator spike, whereby single longitudinal mode operation of the laser is enhanced. A pair of quarter wave plates are disposed on opposite sides of the laser gain medium within the optical resonator to make the power density distribution within the laser gain medium more uniform, thereby further enhancing single longitudinal mode operation. In a preferred embodiment, the trigger circuit includes a divider which is responsive to the detected oscillator spike signals and divides the received spike signals by two or more so that the laser is caused to fire upon initiation of the second or subsequent relaxation oscillator spike.

Active Q-switched high power single mode laser

A meniscus lens is disclosed for use in high power light beam applications, such as in the optics of a high power laser where the laser beam intensity is in excess of one megawatt per square centimeter. The meniscus lens is designed such that light rays reflected from the lens are divergent so that no back focal points are created by the lens. In this manner, undesired dielectric breakdowns and damage to optical components and the like are avoided due to reflected back focal points. In one embodiment of the present invention, the output mirror of a high power laser is deposited upon the convex face of a meniscus lens, such lens being designed to avoid back focal points, whereby the construction of the output mirror is greatly simplified.

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Menlo Park, CA, United States of America

Richard L Herbst