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The output characteristics of a toric unstable resonator fitted to a multichannel stripline excitation system are presented. The resonator is shown to possess the usual advantages of a conventional unstable resonator plus the ability to modify the profile of the output beam by a simple change in the coupling aperture. Laser output parameters have been studied as a function of coupling fraction, magnification, and internal loss factors. Variations in the focal spot size as a function of the coupling aperture as well as resonator alignment sensitivity and polarization properties have been investigated.

The optical performance of a cw PIE CO(2) laser has been substantially improved through the adoption of a burst-mode gain switching technique. The approach has provided a doubling of the average beam power extractable from the device. With appropriate optimization, the process could possibly permit the attainment of pulsed energy extraction in the kilohertz range, and with average optical powers within the several tens of kilowatt category.

The design and operational features of a fluid-ballasted electrode structure for a high powered EDL CO(2) laser are described. This new device incorporates a crossed-tube geometry and as such is much simpler and inexpensive to fabricate than previous multielement or pin electrodes. Hot boundary layer formation at the electrode surfaces is minimized by a ducted flow-through feature also incorporated into the structure. This further assists in suppression of glow-to-arc transitions. The modular design used allows easy scaling to very large discharge volumes. A 40-liter cw CO(2) laser discharge system has recently been developed using this simplified crossed-tube fluid-ballasted electrode pair concept.

Photon absorption and photoionization spectra in a CO(2) laser mixture seeded with selected low ionization threshold additives are presented. Such data are used to determine total absorption and ionization cross sections for some gases and vapors of interest. The results identify tripropylamine as an interesting seedent material, as it exhibits a longer wavelength photoionization effect essentially independent of the primary host laser gases.

The beam quality of a radial laser array, quantified in terms of the M(2) propagation constant, is determined as a function of array element configuration. A lower bound on array M(2) is estimated for both phase-locked and nonphase-locked conditions. It is shown that, to achieve near-unity M(2) array, either aperture filling or spatial filtering is required in addition to phase locking. An aperture-filling method suitable for radial arrays of CO(2) slab lasers is presented.

A unique advancement in the flexibility of high-power lasers is presented. Operation of a 20-kW, continuous-wave, CO(2) laser with a burst excitation technique produces a broad range of optical output characteristics. A detailed discussion of the discharge excitation of this system demonstrates some unique features of the process. Control of burst frequency and duty cycle provides a convenient means to alter the time-varying nature of the output beam. Laser output can be varied from distinct, independent pulses through to a continuous wave. Optical pulse shape varies from triangular to square in profile. The primary focus of this study lies in the regime with distinct, separate pulses. Empirical relationships that summarize the dependence of optical duty cycle and peak laser power on discharge control parameters are developed. Use of these relations imparts control of the optical parameters of importance in deep penetration welding.

An electronic laser controller, based on a computer vision system, has been developed for automatic mode and power control of a high powered CO(2) laser. The cross-sectional image of a sample of the output beam is continually analyzed and used to servo regulate both the laser cavity and the excitation level of the discharge. The technique stabilizes average laser output power to within 4%, while maintaining the best output power distribution achievable by the particular laser. Control system design also provides important on-line beam intensity profile data to assist in maximization of operating efficiency.

Initial small scale experiments have demonstrated the ability of relatively weak Lorentz J × B forces to suppress electrothermal instabilities in coaxial laser gas discharges. However, the effective scaling of such plasmas to the much larger volumes required for high-power laser applications has been found to be considerably more difficult than anticipated. In practice, it has been necessary to incorporate a multielement electrode and external ionization to achieve acceptable performance. This paper describes the design features of such a large volume Magpie (magnetically stabilized, pulse ionized, electrically excited) discharge system and presents the electrical and thermal characteristics of the resulting magnetically stabilized radial plasma. These are discussed in relation to eventual high-power CO2 laser applications.

The design, construction, and operational characteristics of an optical resonator for an annular gain media are described. The system, developed for laser power extraction investigations in a new type of coaxial discharge geometry, features a folded multipass unstable resonator concept, fabricated from lightweight uncoated diamond-turned aluminum substrates. The resulting cw CO2 device incorporates excitation aspects of the nonself-sustained PIE excitation process in addition to a new magnetic discharge stabilization technique. Laser performance and output beam characteristics are presented.

A theoretical investigation of a stable concave-convex resonator configuration, which appears suitable for single-mode high-power energy extraction from large volume gain media, is presented. The design features annular output coupling with a surprisingly uniform near-field intensity distribution. The computer-based analysis, supported by preliminary experimental results, suggests that acceptable alignment tolerances are provided along with an unusually small beam divergence. With proper design, a far-field divergence of 0.5 mrad, encompassing near 80% of the total laser energy, appears feasible. Operational data, recently obtained with this optical extraction approach, have revealed a further important practical advantage over an unstable resonator, being far less prone to mode degradation and hot spot formation on optical component misalignment.

The constructional and operational aspects of a low voltage transversely excited gas transport CO(2) laser are presented. This compact device incorporates a recirculating wind tunnel type geometry and possesses features of the gas dynamic, gas transport, and TEA lasers. The structure with an active length of 36 cm produced a cw power of approximately 200 W at an over-all system efficiency of 5% using a discharge potential of 1200 V.

A report of experiments on low voltage excitation of cw CO(2) lasers is presented. Pertinent plasma considerations are given along with the design of various electrode configurations tested. Preliminary results suggest that low voltage excitation of cw CO(2) lasers is practical using a grid structure and an inverted brush cathode assembly in a reduced height transverse geometry. The positive resistance V-I characteristics so obtained permit an order of magnitude reduction in external ballast.