The basic principles for design of an advanced multi-terawatt СО2 laser system are considered. The key amplifiers' parameters were evaluated by numerical modeling. The potential advantage of using pulsed chemical DF–CO2 laser as a final amplifier over an electro-ionization TE-CO2 laser is outlined. The dynamics of noise development along the chain of amplifiers and a resultant contrast ratio are analyzed. The evaluated parameters allowed to suggest a system with a mid-pressure final DF–CO2 laser which can generate a single 15-TW 2.5-ps pulse.

Multi-terawatt picoseconds 10-μm СО_2 laser system: design and parameters' control

Rotational-Vibrational Structure of CO2.- Laser Processes in CO2.- Continuous Discharge Lasers.- Fast Flow Systems.- Pulsed Systems.- AM Mode Locking of TEA Lasers.- FM Mode Locking of TEA Lasers.- Passive Mode Locking.- Short-Pulse Amplification.

The CO「下2下」 laser

A small size pulsed CO2 laser with rounded edge flat profiled electrodes and variable gas pressure in 1–3 atm range has been constructed and characterized. The perionization system consists of a pair of 16 series-connected spark gaps located along either side of the main electrodes by which, the number of required preionization capacitors is reduced to 4. Sharpening of the main discharge has been performed using a 300 pF peaking capacitor. A maximum energy of 160 mJ/pulse was obtained for CO2:N2:He≡1:1:8 gas mixture and 33 kV discharge voltage. By increasing the laser gas pressure in 1–3 atm range, the duration of spike and tail parts of the laser pulses have been reduced from 110 ns and 4 μs to 37 ns and 1 μs, respectively.

A small size 1-3 atm pulsed CO2 laser with series-connected spark gaps ultraviolet preionization.

A new high-speed photorecorder, ITMGT-device (ionization type magnifying glass of time), is presented which unlike the well-known analogs operates in a wide spectral range of 1.3 - 10.6 micrometers and is intended to record frame by frame the beam structure of laser IR radiation. ITMGT has a wide dynamic range (not less than 300) and high sensitivity (10-4 - 10-5 J/cm2) in a wide spectral region. It provides frame recording with an exposure length of a frame of 10 - 50 microsecond(s) , framing rate up to 100 Hz, and up 100 frames for one recording cycle. It was successfully used to measure divergence and energy density distribution at the end of pulsed and pulsed-periodic IR lasers, in facilities for laser isotope separation and also in development of new industrial technologies for processing, welding, and cutting of materials with the help of high- power laser radiation.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Photorecorder of pulsed-periodic IR radiation based on the ionization chamber

A train of microbunches generates in a passive dielectric-loaded waveguide an electromagnetic wake which propagates at the speed of the particles. This wake consists of propagating modes provided the electrons exceed the Cerenkov velocity. If the material is replaced with an active dielectric, identical to that of a laser, the wake is amplified. Another train of bunches, lagging many wavelengths behind, may be accelerated by this amplified wake. The gradient is limited by breakdown and saturation of the medium. Beam loading may be partially or even completely compensated by the gain along the trailing bunch. Preliminary results of a linear theory will be presented, assuming a 300 MeV beam and high-pressure CO2 mixture as an active medium. In spite of many hundreds of modes excited by the front beam, the spectrum of the amplified field corresponds to a monochromatic wave determined primarily by the bandwidth of the medium. The analytic approach facilitates simple assessment of the effect of the various parameters on the accelerating gradient.

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2D theory of wakefield amplification by active medium

The paper discusses the problem of developing superatmospheric pressure CO2-amplifiers intended to amplify picosecond light pulses. The advantages of the systems for active medium excitation by a soft X-ray preionized self-sustained discharge are demonstrated. The characteristics of the CO2-amplifier with a 5 cm interelectrode gap and a gaseous medium pressure up to 5 atm are presented.

Development of excitation system for a large-area high-pressure CO2-amplifier

In this paper the design features and the results of studying an amplifier for a picosecond terawatt CO2-laser facility are given. The active medium of the amplifier (a CO2–N2–He gas mixture) is excited by a self-sustained volume discharge. The amplifier with an aperture of 0.1 m×0.1 m and with an active medium volume of 10 l provides the possibility for amplifying the 10 μ m radiation of a picosecond laser up to the terawatt power level. A volume discharge at a pressure of 10 atm and at a molecular gas content of 5% with a power input level of 80 J l−1 atm−1 was initiated. The optical gain constant of a small signal of the amplifier active medium was 0.027 cm−1 at a pressure of 8 atm, which confirms the possibility of high-pressure amplifier use as a final amplifier in picosecond CO2-laser facilities with a power output level of 1–10 TW.

Laser amplifier for picosecond CO2 facilities of terawatt power level

CO2 laser system generating the train of ~200 ps pulses with total energy up to 5 J was put in operation in General Physics Institute of Russian Academy of Sciences (IOFRAN) recently. Initial ~100 ps 10.6 ?m laser pulse with energy 10 ?J was regeneratively amplified in 5 x 5 x 5 cm3 discharge volume X-ray preionized TB-CO2 discharge unit developed and manufactured in D.V.Efremov Scientific Research Institute of Electrophysical Apparatus (NIJEFA) in cooperation with JOFRAN. The results on upgrade of this unit towards obtaining 10 atm volume self-sustained discharge in C02:N2:He mixtures with reasonably high percentage of molecular gases are reported. Owing to this upgrade free running mode laser radiation energy B1 (when the unit was equipped with unstable telescopic resonator) at 6 atm was increased up to 22.2 J, which corresponds to specific energy extraction 5.4 J/l/atm and efficiency 4.5%. The estimated value of B1 from such a laser at 10 atm is 15 J. It corresponds to peak power of regeneratively amplified 2 ps 10 ?m pulse formed in master oscillator of laser system N1.5 TW. Prospective of further upgrade of laser system using new 10 x 10 x 100 cm3 discharge volume 10 atm TE-C02 discharge unit which is under construction now in NIIEFA in the network of ISTC Project #1072 is discussed.

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Superatmospheric x-ray preionized TE-CO2 discharge unit

The construction of a CO2 laser system generating a train of subnanosecond laser pulses with total train energy of up to 5 J is reported. A record level of laser energy was obtained due to utilization of unique 5 × 5 cm2 aperture, and 6 atm X-ray preionized CO2 amplifier. The estimations of individual pulse durations in the train are given. The prospect of upgrading the present configuration of laser systems towards shortening laser pulse duration and increasing the pressure of the working gas mixture of the amplifier and its efficiency are discussed.

Wide-aperture picosecond CO2 laser system

Initiation of a self-sustained volume discharge in CO2-containing gaseous mixtures kept under a pressure of up to 10 atm with the aim of amplifying picosecond IR pulses is considered. Experimental electricdischarge and optical characteristics of a wide-aperture high-pressure CO2 amplifier are presented. The feasibility of designing terawatt laser equipment with a master oscillator and preamplifier is discussed.

A. A. Kuchinsky

Papers

Development of excitation system for a large-area high-pressure CO2-amplifier

Laser amplifier for picosecond CO2 facilities of terawatt power level

Superatmospheric x-ray preionized TE-CO2 discharge unit

Wide-aperture picosecond CO2 laser system

Wide-aperture superatmospheric-pressure CO2 laser amplifier pumped by a self-sustained volume discharge