V. R. Sorochenko

Picosecond terawatt CO2 laser system: Picasso-2

Current status of CO2 laser system “Picasso-2” intended to generate 10 μm pulse train with tunable pulses duration 2÷100 ps, interpulse separation ≈ 10 ns and train’s peak power over 1 TW is reported.

Superatmospheric x-ray preionized TE-CO2 discharge unit

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.

Simulation of parametric oscillation in the submillimeter range at pumping of the ZnGeP2 crystal by a train of 100-ps high-power pulses

Analysis is given for a possibility of singly resonant parametric oscillation in the submillimeter range at synchronous pumping of the ZnGeP2 crystal by a train of 100-ps second-harmonic pulses from the CO2 laser with the radiation energy 1.0 J. The calculation shows that using the ZnGeP2 crystal and the second harmonic of the CO2 laser with the energy density 1.8 J cm−2, one can get the peak submillimeter radiation power from 3.6 to 12 MW in the range from 95 to 300 µm (1.0–3.3 THz). The expected peak power values are larger than the experimental ones obtained by other nonlinear optics methods.

Wide-aperture subnanosecond CO2 laser system

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

Wide Aperture Picosecond CO2 Laser System

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

Parametric oscillation of high-power 3-THz pulse by synchronously pumped ZnGeP2 crystal: Computer simulation

Possible parametric oscillation of 3-THz pulse at synchronous pumping of the ZnGeP2 crystal by a train of short second-harmonic pulses from the CO2 laser has been analyzed. Calculation shows that at changing laser pulse duration τ between 4 and 500 ps and correspondingly pumping energy density (0.5–3.5 J cm−2) THz pulse peak power varies from 3 to 70MW with maximum at τ =9 ps.

Frequency doubling of picosecond CO/sub 2/ laser radiation with ZnGeP/sub 2/ crystal

Summary form only given. For mid IR region ZnGeP/sub 2/ crystals have excellent potential for application in nonlinear optics due to unique combination of physical properties. In 1987 second harmonics generation (SHG) efficiency of 49% was realized with this crystal pumped by 2-ns pulses of CO/sub 2/-laser with intensity /spl sim/ 1GW/cm/sup 2/. In the present work SHG was investigated with the ZnGeP/sub 2/ crystals pumped by CO/sub 2/-laser pulses with much higher radiation intensities. To prevent the crystal surface optical damage we applied the significantly shorten laser pulse duration as compared with known data. In our experiments CO/sub 2/-laser system Picasso-2 was used generating the train of pulses with duration 20 - 100 ps and total energy up to 15 J. The system provided laser intensity up to 100 GW/cm/sub 2/ at the crystal samples surface /spl sim/15 /spl times/15 mm/sup 2/. The work was supported by the Russian Fund for Basic Research (grant #03-02-16094).

Toward 1-TW train of 10-μm picosecond laser pulses

The results of principal upgrade of high-pressure, X-ray preionized TE-CO2 laser towards obtaining 10 atm volume self-sustained discharge in CO2:N2:He mixtures with reasonably high (up to 25%) percentage of molecular gases are reported. The estimated energy of radiation from such a laser is greater than or equal to 15 J. It corresponds to peak power of regeneratively amplified 2 ps 10 micrometer pulse formed in master oscillator of laser system greater than or equal to 1.5 TW.

Current measurements in plasma produced by the train of 10.6-um subnanosecond laser pulses

Results of current probe measurements for a plasma produced by the train of approximately 200 ps 10.6 micrometers laser pulses are reported. The train of pulses was obtained as a result of regenerative amplification of approximately 100 ps laser pulse in a 5 cm aperture 6 atm TE-CO2 laser. Experiments were carried out for Wo and Al targets dispersed in vacuum, two values of the interpulses separation in the train (Delta) T equals 9.3 and 29 ns and wide range of energy density on the target, corresponding to peak intensities of single pulses Ip equals 1 divided by 300 GW/cm2. Experiments had shown large difference of temporal structure of current signal with Wo and Al targets due to the considerable different in melting temperatures of these materials as well as radiation loses of laser plasma. We detected large ratio of current signal amplitudes for targets irradiation by the pulse train or gain switched pulse generated in TE-CO2 laser without injection of a short pulse. Results of these measurements are compared with those earlier obtained for nanosecond pulse train.

Probe investigations of close-to-surface plasma, produced by CO2 laser nanosecond pulse train

Investigations of currents in close-to surface plasma, produced by CO2-laser radiation of different temporal structure have been carried out. The character of evolution of registered currents temporal structure at growing energy density was different when the target was irradiated in air and in vacuum by the train of short (τ = 2.5 ns) pulses. Experiments in vacuum have revealed that the transit from smooth single mode pulse to the nanosecond pulse train of the same total energy was followed by a considerable decrease in plasma formation energy thresholds and by the increase of amplitudes of currents induced by plasma. The current pulses from the target were registered after finishing the laser irradiation; their appearance was probably connected with cumulation effects, caused by the ring form of the irradiated area.