A high-pressure CO2 laser with large discharge x-section of 22×22 mm and gain length of 800 mm has been developed for use as regenerative or multi-pass amplifier in high energy ps laser systems. A test system with reduced electrode length was constructed to establish initial design parameters for the full-size system. The design of the final amplifier is described, and measured performance characteristics are presented. The system can be operated at gas pressures of up to 12 bar and provides stable discharges with a small signal gain of >3 %/cm. Further scaling of the laser to x-sections of up to 50×100 mm will be discussed and preliminary results of a discharge test system for development of novel discharge excitation techniques will be presented.
Laser Ultrasonic Testing (UT) is an important technique for the non-destructive inspection of composite parts in the aerospace industry. In laser UT a high power, short pulse probe laser is scanned across the material surface, generating ultrasound waves which can be detected by a second low power laser system and are used to draw a defect map of the part. We report on the design and testing of a transversely excited atmospheric pressure (TEA) CO2 laser system specifically optimised for laser UT. The laser is excited by a novel solid-state switched pulsing system and utilises either spark or corona preionisation. It provides short output pulses of less than 100 ns at repetition rates of up to 1 kHz, optimised for efficient ultrasonic wave generation. The system has been designed for highly reliable operation under industrial conditions and a long term test with total pulse counts in excess of 5 billion laser pulses is reported.
Results obtained from a small discharge cross section (10×10 mm), high pressure (10 bar) TE CO2 laser are presented demonstrating continuous wavelength tunability of the laser. Two arbitrary wavelength regions in the 9P and 10P branches are chosen to demonstrate the continuous tunability of the laser wavelength. Furthermore stability of the laser output is demonstrated over extended periods of operation. Other output parameters of the high pressure laser such as temporal pulse profile and peak pulse power were also measured. Preliminary results will be presented of a discharge system scaled to larger discharge cross sections intended for high pressure amplifiers in ultra short pulse terawatt laser systems. Electrode separations of up to 50 mm have been investigated with measured discharge widths of 80 mm. The system has been operated at gas pressures of up to 3.5 bar with various CO2 laser gas mixtures. Discharge stability studies and gain measurements are reported.
Results are presented on the influence of acoustic waves on the performance of high-repetition-rate TEA CO2 lasers. It is shown that acoustic waves generated inside the laser cavity lead to nonuniform discharges, resulting in a deterioration of the laser beam quality, decreased output energy, and an increase in pulse-to-pulse energy variation. The effect of the gas mix on the acoustic behavior is investigated, and experimental results on laser performance across a range of gas mixtures are presented. Methods to reduce the effects of acoustic waves are presented together with experimental results. The influence of acoustic damping measures on laser gain are demonstrated, showing a significant improvement in gain and output power at high pulse repetition rates.
In this paper we present results on the influence of acoustic waves on the output laser beam from high repetition rate TEA CO2 lasers. We show that acoustic waves generated inside the cavity lead to deterioration in beam quality, decreased output energy, and an increase in pulse to pulse energy variation. We investigate the impact of gas mix on the acoustic behaviour, and present experimental results on laser performance across a range of gas mixtures. Solutions to the acoustic wave problem are presented together with experimental results. The influence of acoustic damping measures on laser gain are demonstrated showing a significant improvement in gain and output power at high repetition rates. The link between the pre-ionisation method employed and the acoustic wave impact on laser performance is discussed.
The IGBT (Insulated Gate Bipolar Transistor) is a modern solid-state switch with wide spread applications in power electronics. However, little information is available on the performance and reliability of
the switch in pulsed power supplies used for the excitation of CO2 TEA and excimer lasers. Results of reliability test conducted on a high-power, high-voltage IGBT are presented with additional focus on the measurement technique. It is found that IGBTs can be reliably used in pulsed power supplies where the peak switching current exceeds the average current rating up to five times. Furthermore, IGBTs can be reliably connected in series to increase the switch operating voltage.
We report on the construction and optimization of a TEA CO2 laser with a discharge volume of 15 cm3 and cavity length of 20 cm. Such a short cavity facilitates single longitudinal mode operation. A roots blower is employed to achieve the necessary gas flow rate for highrepetition-frequency operation in a compact design. Output has been obtained at 1 kHz and a stable discharge to a repetition rate of 2 kHz has been demonstrated. The laser is part of a program aimed at the development of an efficient laser system for molecular laser isotope separation. Additional applications in materials processing are envisioned.
A continuously tunable 3-atm mixed isotope CO2 oscillator power amplifier (MOPA) chain is developed for a molecular laser isotope separation pilot plant. The characteristics of this laser such as tunability, bandwidth, and output energy are reported. A closed loop gas flow system with a catalyst is employed and its performance is reported.
We have developed a high repetition rate high average power pulsed laser system intended for industrial applications. The system has been designed for operation as an excimer and CO2 TEA laser and is capable of continuous operation at repetition rates of up to 2 kHz. A closed loop gas recirculation system, driven by a large diameter, magnetically coupled, axial fan is employed, providing gas flow velocities of up to 90 m/s. The laser delivers maximum average output powers of more than 500 W as KrF excimer and 2.5 kW as C02 TEA laser.
KEYWORDS: Power supplies, Solid state physics, Pulsed laser operation, Solid state lasers, Capacitors, Gas lasers, Prototyping, Switching, Magnetism, Excimer lasers
Excimer- and CO2 TEA pulse lasers require excitation pulses with voltage rise times of 100 ns and peak voltage levels of more than 40 kV for efficient excitation. The corresponding electrical inputs extend to multikilowatt levels of average powers. To achieve these levels, primary switching must be carried out at tens of kA and multiple kV levels and at repetition rates of several kHz. These requirements place extreme demands on the active switching elements employed in the pulser for primary pulse conversion. Under these conditions, thyratron lifetimes are drastically limited and endeavours to overcome these limitations have led to the development of an all solid state driven pulser. The solid state driven pulser employs a modular, thyristor switched, pulse power supply unit for primary pulse conversion and a four stage series magnetic pulse compressor to transform the pulses into a domain compatible with excimer laser excitation.
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