Whispering-gallery CO2laser

The design and operation of a CW CO2laser based on the whispering-gallery principle is reported. The optical cavity consists of a portion of the equatorial region of a torus terminated by two flat mirrors. In agreement with theoretical expectations, the output beam is found to be TE polarized, and to consist of low-order Airy-Hermite-Gaussian modes.     

Q-switched CO2laser

Experimental studies of a rotating-mirrorQ-switched CO2laser have been undertaken to obtain high peak powers at 10.6-μ wavelength. TheQ-switched pulse has a temporal structure consisting of two intensity peaks and is similar to the temporal behavior of a slowQ-switched CO2laser. Based on the gas pressure dependence it appears that the pulse structure and duration are influenced by collision-induced relaxations of the laser medium. Using an oscillator-amplifier system peak powers of 120 kW with pulsewidths of 200 ns have been obtained.     

Frequency modulation of a self-mode-locked dual-polarization CO2laser

Simultaneous active stabilization and frequency modulation of a mode-locked dual-polarization CO2laser is reported. Mode locking was maintained during frequency modulation through use of a self-regenerative feedback technique.     

Folded-path atmospheric-pressure CO2laser

A folded-path transversely excited atmospheric-pressure CO2laser utilizing shower or brush discharges is described. The output pulse has an initial peak 0.4 μs wide followed by a tail2-3 mus long. A peak power of 0.2 MW with 4.4 percent efficiency is obtained. By rotating one of the mirrors of the resonator the tail is eliminated, yielding a pulse 0.2 μs wide of the same peak power.     

CO2laser mode locking produced by sinusoidal cavity-length modulation

Mode locking of a CO2laser through the use of cavity-length modulation is reported. A cavity end reflector was sinusoidally modulated along the cavity axis at a frequency equal to the quiescent axial mode interval. Phase-locked pulsing occurred at a rate equal to or twice the axial mode interval.     

Intracavity polarization modulation of a nearly isotropic CO2laser

A simple intracavity polarization-modulation technique is described that shows promise of producing nearly 100 percent amplitude modulation of laser output through the use of a relatively low-voltage electrooptic birefringent modulator. Some preliminary performance data are presented that support the general feasibility of the technique and indicate the direction that should be taken toward its further development. Although the technique is generally applicable to any CW laser system, it would appear to be particularly useful with the CO2laser since good electrooptic modulators are not available for that laser.     

Thin film-coated waveguide CO2laser

A new type of radio frequency (RF) excited waveguide laser with a rectangular cross section is proposed which is composed of two dielectric or lossy materials and two metallic electrodes which are coated by a thin film with small absorptions. Theoretical and experimental analyses show that the maximum output powers of the new waveguide laser are much larger than those of conventional ones.     

Simultaneous CO and CO2laser

CW laser action at both the 5- and 10.6-μm wavelength regions has been achieved simultaneously from CO and CO2molecules in a slowly flowing mixture of He-air-CO. Two dc discharges through the premixed gases within a segmented laser cavity were used to provide molecular excitation and generate CO2molecules by discharge-initiated CO oxidation. Both liquid nitrogen and room-temperature water cooling were used concurrently. A total power of about 2 W has been achieved with approximately half the power in each wavelength region.     

Large aperture CO2laser discharges

Large aperture high-pressure gas laser discharges are a prerequisite for the development of high-energy gas lasers of sufficient power for the production of plasmas of thermonuclear interest. Of the several approaches being followed toward the attainment of such discharges, one utilizing weak volumetric preionization of the active gas region produced by UV radiation is described. The use of this technique has resulted in the successful generation of atmospheric-pressure CO2laser discharges between electrodes separated by 30 cm, having total cross sections of ∼600 cm². With input energies of ∼200 J/1 small signal gain values of 4-5 percent cm^-1were measured in 1 : 1 : 3 gas mixtures of CO2, N2, and He, respectively. It is thus concluded that this excitation technique could be incorporated into the fabrication of large volume gas laser amplifiers having beam cross sections in excess of 10³cm²and total output-energy capabilities ofsim 10^{4}J.     

Q-switching of the CO2laser

The laser pulses obtainable from aQ-switched CO2laser are calculated and compared with the results of a number of different techniques of performing theQ-switching. The continuously operating laser is considered first. The transition rates between the molecular vibrational states and their occupations are derived from the measured CW power. The laser tube was 1.9 meters long, had a diameter of 2.4 cm, and used flowing CO2-N2-He gas. For rapidQ-switching, maximum pulses of 4.5 mJ energy and 85 ns half width are predicted. Such pulses were observed with a rotating mirrorQ-switch. However, that technique has a limited pulse repetition rate and experiments on closely spaced pulses are difficult to interpret. A more flexible technique, which allows a much greater variation in the experimental parameters, is the use of a fast shutter to interrupt the laser beam in the cavity. While this switch is somewhat slower than the rotating mirror it does produce pulses of the same energy at repetition rates up to 5000 per second, and smaller pulses at any desired higher rate. From these measurements the upper and lower laser level lifetimes are deduced. They are found to agree well with the values obtained from the CW measurements.     

Mixed isotope multiatmosphere CO2laser

A sealed transversely excited multiatmosphere pulsed laser is reported in which the active media is a combination of three isotopes:¹²C¹⁶O2,¹²C¹⁸O2, and¹²C¹⁶O¹⁸O. Lasing action is obtained on all 12 vibrational-rotational bands with continuous tuning observed between line centers at pressuresfrac{1}{2}tofrac{1}{4}of those required with conventional¹²C¹⁶O2lasers.     

Single mode CO2laser frequency modulation up to 350 MHz

Experiments on internal frequency modulation (FM) of a CO2laser showed no limitation of FM by the linewidth. However, distortions in the form of strong enhancement of sideband amplitude arise for frequencies equal to the cavity resonant frequencies, most pronounced if the modulator is positioned near a cavity mirror.     

A pin-electrode atmospheric-pressure CO2laser

A 1.2-m-long transversely excited atmospheric-pressure (TEA) CO2laser utilizing shower discharges is described and its operating characteristics as a function of voltage examined up to 60 kV. Pulse energies in excess of 2 J, peak powers in excess of 20 MW, and efficiencies up to 15 percent have been achieved.     

Prediction of CO2laser signatures

Based on previous work, a method is presented to predict the signature of a CO2laser, i.e., the output power as a function of the cavity length. For that purpose the normalized laser intensity curve versus cavity length is determined for a single line. The calculation is based on a homogeneously broadened line (Lorentzian shape) and takes into account the line dispersion. The curve is a parabola and its shape is assumed as being the same for all lines considered. From calculated positions of line centers and small-signal-gain data the signature can be drawn with the help of a parabolic French curve. The transition from one line to the next is assumed to occur at crossings of the normalized intensity curves. The theory agrees well with the experiment.     

High-power TE CO2laser with graphite electrodes

A high-power CW TE CO2laser using a new graphite anode structure and a novel Mo wire cathode is described. A uniform discharge for laser excitation is obtained. The device produces a CW output of 6 kW.     

Single-wavelength CO2laser without dispersive elements

Observation of single-wavelength operation in a TEM00mode laser at the 80-W level without the use of intracavity dispersive elements is reported. The output wavelength remains at theP(20)line irrespective of cavity length changes, gas mixture, and excitation level for cavity lengths of about 4 m or longer.     

A radiatively pumped CW CO2laser

A proof of principle experiment to demonstrate the physics of a radiatively pumped laser has been carried out. For the first time, a blackbody cavity has optically pumped a CW CO2laser. Results are presented from a series of experiments using mixtures of CO2, He, and Ar in which maximum output power was obtained with a 20 percent CO2- 15 percent He-65 percent AR mixture. The dependence of the output power on the blackbody temperature and the cooling gas flow rate is also discussed. By appropriately varying these parameters, continuous output powers of 8-10 mW have been achieved.     

High repetition rate TEA CO2laser

This correspondence reports on the successful operation of a TEA CO2laser at rates up to 1000 pps with an average output power up to 65 W over long periods of time. An essential feature of the present system is a rapid gas circulation transverse to the laser axis combined with a large volume of ambient gas. It is found that decomposition of the gas is one of the major problems at high repetition rates.     

Variable attenuator for CO2laser radiation

A gaseous absorption cell variable attenuator for 10.6-μ-wavelength radiation, which uses forced convection to eliminate thermal defocusing effects, is described. The device is capable of attenuating high-intensity CO2laser radiation with negligible distortion, and results are shown for an experimental model used at an intensity level of 100 W/cm².     

A high-power CO2laser radar transmitter

Experiments on the amplification of CW and pulsed infrared signals at 10.6-μ, wavelength have been carried out on CO2laser amplifiers excited by dc and pulsed electrical currents. Measurements of low signal gain, gain saturation, repetitive pulse amplification, and optical distortion have led to the design of a 1-kW average power transmitter with 10-μs infrared output pulses. The design, construction, and performance of this device are discussed. Measurements of pulse shaping, pulse-to-pulse stability, output beam divergence, and stability are outlined.