Recent work in the area of rf pumped CO, waveguide lasers has led to the development of high repetition rate pulsed rf devices. Thgse lasers typically exhibit self-polarized, gain-switched outputs with remarkable amplitude and frequency stability. Peak output powers of nearly 800 watts have been observed at kilohertz repetition rates in 20 cm long devices. Minimal degradation in average power after 109 pulses has been observed during sealed-off operation in one such device.
The transverse RF discharge plasma characteristics of He:N2:CO2 gas mixtures used in CO2 waveguide lasers has been predicted and measured. Using theoretical electron transport coefficients and a classical RF plasma model, predictions of discharge conductance, E/N, and excitation efficiency were obtained. Experimental values of gas conductance and E/N were reduced from measurements of laser voltage and input power. Laser efficiencies of 15% have been attained.
A low cost, four watt CO2 laser intended for use as either an expendable beacon or expendable source for proximity fuses has been developed by the Hughes Aircraft Company, The laser, excited by a 100 MHz RF power supply, has a modulation rate capability extending from d,c, to over 100 kHz, The laser, dc-dc converter, and RF power supply weigh less than 1 kg, Although most of the intended applications require the laser to operate for only a few seconds, it has been tested for over 600 hours with negligible power degradation,
This paper describes the design and output characteristics of a series of continuous(CW) waveguide lasers in the range of output powers from 2 to 15 Watts. These lasers are internal mirror systems made of a single block of alumina resulting in an extreme miniaturized and ruggedized configuration suitable for military applications. Conversion from CW operation to repetitive pulsed operation is possible by using an RC-network for excitation (relaxation oscillator). A high pulse-to-pulse stability of 1 part in 105 has been achieved using a synchronization oscillator.
The design and performance of a uv preionized CO2 oscillator with integral four-pass amplifier is described. This laser is operated at any pressure from 1 atm to 10 atm without the necessity of complex Marx bank electronics. A Q switch is required in the oscillator cavity to delay the oscillator pulse until the peak gain of 4.5/m can be reached. Even without the use of a Q switch to optimize performance, the laser has produced 700 mJ, 1 ns FWHM CO2 laser pulses.
A compact atmospheric-pressure hybrid CO2 laser utilizing a transverse double-discharge technique has been constructed and operated at moderate repetition rates. A pulse output energy of 80 nil has been obtained under single-mode conditions at repetition frequencies of 100 Hz. Using the hybrid technique to obtain single-longitudinal-mode operation, we have been able to reach a 7-kHz long-term relative frequency instability between the TEA laser and a local oscillator laser. Measurements of the frequency sweeping during the pulse tail (chirp) are also presented along with a direct measurement of the resonant frequency pulling effect associated with the real part of the electric susceptibility of the gas. Limitations on the pulse repetition frequency for this laser configuration are also discussed.
This paper reviews a technology developed recently for surface corona (UV) preionization stabilization of high-pressure glow discharges. The techniaue is well suited to transverse excitation of compact lasers. The paper specifically illustrates how the scheme was successfully applied to the development of CO2 waveguide lasers and reviews the main proper-ties of these devices.
A number of pulsed carbon dioxide lasers have been developed to form the basis of laser systems operating at a wavelength of 106 microns. A compact sealed-off CO2 TEA laser which has an output power of 220 kW and a lifetime in excess of 106 pulses, is at an advanced stage of development. This laser employs trigger wire initiation of the main discharge. Arc array initiation has also been employed to provide a means of extending the stable operating regime. As a consequence, output powers in excess of 1.2 MW have been achieved from a sealed-off polarised laser. In addition, an experimental trigger wire initiated laser employing a tangential fan to produce transverse gas flow in the active discharge region, has been operated at repetition rates of up to 100 Hz.
Laser rangefinders for fire control applications and laser designators for semiactive guidance of precision projectiles demonstrated their utility in combat situations in Vietnam. The first laser rangefinder used a pulsed ruby laser; however, the low repetition rate limitation of the ruby laser precluded its use as a designator. A further disadvantage to ruby lasers is their visible radiation which, of course, is detectable by the eye. Ruby lasers were soon replaced by neodymium doped yttrium aluminum garnet, YAG:Nd+3, lasers which, because of their higher pulse repetition rate capability, could be used in designator applications as well as for rangefinders. Through continued research and development these devices eventually became sufficiently lightweight to not only become manportable designators, but also rangefinders which could be used in the same way as binoculars are employed. A number of rangefinders and designators are currently in production or about to be put into production. Approximately a decade ago, clisideration was given to the possibility of using CO2 lasers as rangefinders and designators. As with YAG:Nd -I devices, the work has initially been concentrated on rangefinders. These devices have advanced to the stage where three models one from Honeywell, one from Raytheon and one from Marconi have been delivered to the Army Night Vision and Electro-Optical Laboratory for evaluation. In addition, Hughes Aircraft Company will use a Marconi laser in a CO2 rangefinder for the XM-1 tank.
A survey of techniques for combining active laser functions with passive thermal imaging systems is presented along with some recent accomplishments. Emphasis is placed on the advantages of integrating CO2 lasers with the 8 - 12 μm thermal sensors arising from the commonality of operating wavelengths. Compatibility of performance, eye safety and sharing of optical components are pointed out as the primary driving factors which favor CO2 lasers. Recent accomplishments include the development of the first U.S. CO2 laser range-finder which has been integrated with the thermal sensor for a high survivability test vehicle (HSTV). A fully modularized, sealed-off CO2 TEA laser rangefinder developed for the U.S. Army is also described.
Before a rangefinder or target designator design can be specified, the relationship between laser transmitter, receiver and range variables must be well understood. This paper presents results of calculations performed for that purpose using a rangefinder/designator systems model. Specifically, laser transmitter parameters such as wavelength (1.06, 3.8 and 10.6 micron), energy and pulsewidth and receiver parameters such as specific detectivity, field-of-view, signal-to-noise ratio and detector physical size were evaluated for numerous atmospheric conditions including rain and battlefield smoke. Target range was used as the primary basis of comparison. Major conclusions from the study were: (1) 10.6 micron wave-length is preferred for rangefinding and target designation when considering all weather, real battlefield operation, (2) for optimum performance, high pulse energy and short pulse width are desirable, (3) pulse energy per root pulse width of 100 to 1000 J-sec-1/2 are recommended, (4) pulse energy per root pulse width varies logarithmically with range, thus pulse energy can be reduced substantially while producing only small variations in range, (5) performance improves when field-of-view and detector size decreases and signal-to-noise ratio and specific detectivity increases, and (6) the most sensitive receiver parameters were found to be detector size and field-of-view.
Rangefinders operating at a wavelength of 10.6 microns have good performance in conditions of poor visibility, are optically compatible with thermal viewing systems and are eye-safe; these advantages are particularly important for military applications. To demonstrate the feasibility of rangefinding at this wavelength prototype pulsed carbon dioxide (002) laser rangefinders have been developed. The prototype equipment has a mod-ular construction and uses a Marconi Avionics sealed off CO2 transversely excited atmospheric (TEA) laser tube in the transmitter unit. The receiver unit smploys germanium optics and a lead tin telluride (LTT) detector which is cooled to 77 K. Trials of this laser rangefinder have been conducted against a variety of targets and a ranging performance of up to 9 km with an accuracy of + 5 m has been demonstrated.
A scanning laser doppler anemometer system for the remote measurement of atmospheric turbulence has been developed. The system has been operated on an exposed airfield site and has demonstrated the feasibility of long range laser anemometry.
The system described here uses a CO2-TEA-laser that operates at 2pps with a pulse peak power greater than 300KW. Independent optical trains are used with a transmitted beam divergence of 0.5 mrad and 5-inch diameter receiving optics. A high-speed HgCdTe photodiode with a responsivity of a D* = 1.34 x 10 'cm Hz 2/W is used in the straight detection mode for detecting the leading edge of the pulse return from the target. The unit has been field-tested and range data from many natural and man-made targets has been obtained.
The CO, TEA Laser Rangefinder can be utilized for both ranging and information transfer by modulating the tail of the CO2 TEA laser pulse. This multifunctional capability for the CO, laser rangefinder is achieved by pulse code modulation with an electro-optic modulator. A CdTe crystal Pockels Cell used in a double-pass configiration has produced a train of optical pulses 100 nanoseconds wide at 5 MHz repetition rate.
The development in recent years of high-performance, wide-bandwidth HgCdTe photodiodes has led to greatly increased CO2 laser heterodyne system capabilities in the GHz region. Near-ideal heterodyne performance has been obtained, not only with single photodiodes, but with quadrantal and 12-element photodiode arrays. Wide-bandwidth photodiode design considerations, fabrication, and heterodyne evaluation techniques and results are presented here, along with a discussion of the factors that limit heterodyne performance and the feasibility of extending the bandwidth into the 5 to 10 GHz region.
This paper presents the results of the first CO2 laser heterodyne measurements performed on boron implanted n+-p Hg0.8Cd0.2Te photodiodes. The measured data shows that this type of device structure is capable, of achieving bandwidths -20 of approximately 475 to 725 MHz and noise equivalent powers of 3.2 x 10-20 at 77 K and 1.0 x 10-19 W/Hz at 145 K.
This paper presents experimental results describing the dc and CO2 laser heterodyne characteristics of single element and four element n+-n--p Hg0.8Cd0.2Te photodiode arrays. These diodes exhibited wide bandwidths (~2.0 GHz) and fairly good effective heterodyne quantum efficiencies (~13-30% at 2.0 GHz). Typical noise equivalent powers of approximately 1.44 x 10-20w/Hz to 6.23 x 10-20w/Hz have been measured at 2.0 GHz.
Advances in the technology of fabricating IR transmissive fiber waveguides have resulted in the development of fibers that offer unique solutions to near and long-term IR systems problems. Short (<2 m) links of polycrystalline KRS-5 (thallium bromoiodide) fiber have already been successfully used to relay information to remote photodetectors. Future long-distance communications links may take advantage of the extremely low loss potential (~10-3 dB/km) predicted theoretically for a large class of IR fiber materials near 5 µm.
An instantaneous modulation bandwidth of 1 GHz and a mechanically tunable bandwidth of 3 GHz with an efficiency of 27% has been obtained for the output frequency of a CO 2 laserusing the linear electro-optic effect in single crystal CdTe. The microwave (modulating) field is applied on a pulsed basis to reduce crystal damage due to heating. A CW efficiency of 0.15% was obtained. By choosing a particular crystal orientation 90% efficiency was obtained on a pulsed basis.
The interaction of 10 µm radiation with Stark tunable gases can be used to perform a variety of control functions for CO2 lasers. In addition to reviewing some earlier applications) this paper will present results of our recent work on optical limiters, bistable devices, tunable filters, and modulators using novel Stark configurations.
This paper describes the experimental high power coherent 10.6 µm radar located at the Lincoln Laboratory Firepond Facility. The radar utilizes a 48" telescope for the transmission and reception of signals which are processed to perform the automatic angle and frequency tracking functions. The transmitted energy is derived from a closed cycle electron beam excited discharge laser final amplifier equipped with a rotating ZnSe high power output window. A high power multiple rotating disc system performs the pulse forming and receive transmit duplexing functions. The transmit optical path consists of liquid cooled high power metal mirrors to minimize optical distortion due to heating effects. The radar is capable of tracking both enhanced and unenhanced targets in low and medium altitude earth orbit.
Recent developments in the field of tactical infrared radars are reviewed. Experimental studies of imaging properties, weather penetration, and MTI operation are presented. The status of technology developments in the areas of compact CO2 lasers, telescope design, and fabrication and utilization of heterodyne detector arrays is discussed.
The availability of optically pumped farinfrared laser powers in the range from 1 to 100 mW at wavelengths in the range from 30 to 2000 pm has brought out a number of interesting industrial applications for the purpose of material inspection, diagnostics and pro-cessing. This paper summarizes the type of materials and industrial products, which are transparent at these wavelengths and reviews physical phenomena, which are applicable to material diagnostics and quality inspection.