Microwave pumped rare-gas halide mixtures feature excimer laser emission without preionization. The performance of a XeCl excimer laser is investigated with an optimized waveguide coupling geometry. Parameters such as the microwave power, duration of the microwave pulse, and the rise time of the microwave pulse from 25 ns to 220 ns were varied. The pulsed microwave L-band transmitter had a power of up to 10 MW, an adjustable pulse duration (500 ns to 6000 ns), and a pulse repetition frequency up to 400 Hz. The coupling geometry consisted of a double ridge waveguide. The discharge tube was a quartz capillary placed between the ridges. Two tubes were used. One had an outer and inner diameter of 10.3 mm and 2.6 mm, the other 8 mm and 5.8 mm, respectively. The total active length was 438 mm. A study of a microwave power of 2.5 MW deposited into the discharge yielded at low repetition frequencies a non-homogeneous deposition. With a new resonant coupling geometry, a XeCl laser energy of up to 1.8 mJ in a 16 ns long pulse was achieved.
Rare-gas halide gas mixtures such as helium, xenon and hydrogen-chloride were investigated using L-band microwave excitation techniques. For the experiments a magnetron generator with a pulsed power of 2.5 MW, a pulse duration of 4 microsecond(s) and a repetition frequency of 10 Hz, a klystron transmitter with a pulsed power of 10 MW, a variable pulse duration from 500 to 6000 ns, and a maximum repetition frequency of 430 Hz were applied. In a gas mixture consisting of He/Xe/HCl equals 1000/10/0,5 at a total pressure of 1 bar two laser transitions were observed to operate simultaneously. One in the UV, i.e. the XeCl laser, and the second in the IR, i.e. the Xe laser at 2.03 micrometers . It was found the HCl content is important for the Xe laser performance. Up to a factor of 5, more IR laser pulse energy was measured when the HCl concentration of the mixture was optimized. For both lasers almost the same pulse energies were obtained, 15 (mu) J respectively. The pulse duration was 65 ns for the UV and 150 ns for the IR laser. In all experiments the discharge tube had an inner diameter of 2.6 mm and an outer diameter of 10.3 mm. The excited discharge length was 438 mm. However, when a larger cross-section of the discharge tube was chosen, a maximum UV pulse energy of 1.8 mJ in a 16 ns long pulse was obtained.
KEYWORDS: Microwave radiation, Transmitters, Pulsed laser operation, High power microwaves, Waveguides, Gas lasers, Modulation, Pulsed power, Oscillators, Medium wave
To investigate the excitation technique of high pressure gas lasers by high power microwave discharges, a WR-650 waveguide circuit was assembled. The pulsed microwave source was a magnetron transmitter with a frequency of 1355 MHz, a nominal pulsed power of 2.5 MW and a pulse length of 4 microsecond(s) . The pulse repetition frequency was 10 Hz. A double ridge waveguide coupling structure was designed. The results from these experiments have shown the need for a high power broadband modulateable microwave source to achieve further knowledge important for the design of compact, high power microwave excited lasers. For these purposes, a former radar transmitter, based on an amplifier chain terminated by a klystron, was modified. The transmitter has a center frequency of 1400 MHz with an instantaneous bandwidth of 100 MHz, a pulsed power of 10 MW, a maximum pulse length of 6 microsecond(s) and a maximum repetition frequency of 450 Hz. The amplifier chain is driven by a dielectric resonance oscillator which is pulse modulated by very fast pin diodes. This design allows the generation of multiple pulses within the 6 microsecond(s) time window with microwave pulse rise times of the order of ten's of nanoseconds. The results obtained with this equipment will be presented.
Microwave discharges have been used to excite rare gas halide
mixtures like XeC1. For the realization of microwave excited excimer
lasers a minimum specific pump power density of 100 kW/cxn3 is needed.
The resulting power requirements are of the order of one to ten mega-
watts. This power has to be deposited in a discharge tube which is
housed in a hollow waveguide. For these purposes, a WR-650 waveguide
circuit was assembled. The pulsed microwave source was a magnetron
transmitter with a frequency of 1.35 GHz, a pulsed power of 2.5 MW and
a pulse length of 4 jis. The puise repetition frequency was 10 Hz. A
double ridge waveguide coupling structure was designed using the cornputer
code URMEL-T. This program is based on a finite difference discretization
method for the Maxwell field equations to compute electromagnetic
fields in waveguides and cavities. The laser gas mixture consisted
of He/Xe/HC1 = 1000/1/0.2 at a total pressure of 1000 mbar. A
laser pulse energy of 20 pJ with a pulse width of 65 ns (FWHM) was
measured yielding a peak power of 300 W.
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