Parametric Amplifiers of Laser Pulses
Broadband Large-Aperture Optical Parametric Amplifiers of Chirped Laser Pulses Based on KD*P Crystal
Tech Area / Field
- PHY-OPL/Optics and Lasers/Physics
3 Approved without Funding
Russian Academy of Sciences / Institute of Applied Physics, Russia, N. Novgorod reg., N. Novgorod
- VNIIEF, Russia, N. Novgorod reg., Sarov
- University of Rochester / Laboratory for Laser Energetics, USA, NY, Rochester
Project summaryThe petawatt level of laser power can be achieved based on the principle of amplification of time-stretched frequency-modulated laser pulses in traditional large-aperture amplifiers on Nd glass and their subsequent compression up to durations of several hundreds of femtoseconds in a diffraction grating array [1-3]. Further progress towards higher powers is limited by a comparatively narrow gain bandwidth of light in the Nd glass (Dl ~ 30 – 40 nm).
In this regard, various alternatives are being discussed and investigated to overcome the petawatt barrier with more broadband amplification systems.
One of the most interesting and promising schemes relies on the use of parametric light amplifiers instead of conventional laser ones [4, 5]. Here the conditions of broadband phase-matching at parametric amplification are realized, and at the same time, traditionally for super-strong field generation, the principle of successive stretching (frequency modulation), multiple amplification and compression of amplified pulses is utilized.
Investigations of parametric interaction in KD*P crystal, which were carried out in the last two years at the IAP RAS and VNIIEF [6-9], have demonstrated amplification of broad-band chirped pulses with energy ~ 1 mJ in a two-cascade amplifier with nonlinear elements made of KD*P crystal. Experimentally it was shown that, in contrast to KDP, in the KD*P crystal (ooe-interaction) pumped at a wavelength of 527 nm a super-broadband non-degenerated phase-matching at a signal wavelength of l1 ~ 911 nm can be achieved. At this phase matching, the second-order dispersion of wave mismatch approaches zero. Therefore, the gain bandwidth is determined by the third-order dispersion and lies in the range ~ (1500– 2000) сm-1.
Chirped pulses in the super-broadband phase-matching band can be excited by pulses either from a Ti:sapphire laser or a Cr-forserite laser with a conjugated wavelength l2 ~ 1250 nm. Pulse duration of these lasers in a corresponding range reaches 20-40 fs. The results obtained show that the KD*P crystals are very promising for the creation of optical parametric amplifiers of femtosecond pulses up to the multipetawatt level.
The advantages of the proposed optical parametric amplification scheme in the DKDP crystal at a pump wavelength of l3 = 527 nm over conventional quantum amplifiers based on Nd phosphate glass are the following:
- A broad gain bandwidth in the nonlinear KD*P crystal of an optical parametric amplifier, which allows for amplified pulses durations as short as 20 – 30 fs;
- Smaller dimensions of diffraction gratings of the compressor – one of the most technologically sophisticated and expensive elements in high-power systems;
- A considerably lower, in comparison with laser amplifiers, level of amplified spontaneous emission and a resulting high (і 106) contrast of petawatt pulses on target;
- A high (up to 104 – 105) gain coefficient in one cascade, facilitating suppression of self-focusing processes;
- Considerably reduced thermal loading on the amplifying element and a possibility to work in the frequency regime.
Pump pulses of broad-band optical parametric amplifiers can be obtained by converting radiation at a wavelength of l = 1053 nm into the second harmonic, i.e., laser setups on Nd phosphate glass, both the existing ones and those currently under development, can be easily incorporated in the optical parametric amplification scheme.
The implementation of this project will permit to theoretically calculate and experimentally develop underlying scientific principles of optical parametric amplification of broad-band light pulses in multi-cascade systems, and to develop a promising scheme of a large-aperture (beam diameter 100 mm) parametric amplifier of subpetawatt power level based on a KD*Р crystal. Here an important circumstance is that the petawatt and multipetawatt levels of laser radiation power will be achieved at an output energy one order of magnitude lower than in existing systems, therefore considerably reducing the cost of compressor. Successful implementation of the project will open up an opportunity for creating in laboratories relatively inexpensive systems of subpetawatt and petawatt power level. This in turn will benefit research of matter behavior in super-strong light fields for fundamental scientific and applied (technological) purposes.
A number of tasks should be solved to create broad-band large-aperture optical parametric amplifiers. Main of them are:
Task 1. Computation and optimization of parameters of multicascade optical parametric amplifiers.
Task 2. Growth and finishing of KD*P crystals of required size and orientation.
Task 3. Optimizing parameters of a pump system and synchronizing it up to an accuracy of ~ 100 ps with a femtosecond laser.
Task 4. Development of an optical system of the parametric amplifier, a system for excitation and compression of amplified pulses, a system for control of amplifier’s parameters.
Task 5. Experimental investigations of broadband parametric amplification.
The accomplishment of these tasks is the main objective of the Project.
Principal executor of the Project is the Institute of Applied Physics of the Russian Academy of Science (IAP RAS). The IAP RAS cooperators have strong research experience in the area of theoretical and experimental studies of the processes of parametric conversion, amplification and generation of light in nonlinear crystals, and in the investigation of the physics and engineering of lasers with ultrashort pulse durations [6-11]. The IAP has a modern technological and production basis for growth and finishing of large-aperture (sizes ~ 300 ґ 300 mm2) KDP and KD*P crystals. In 1995-1997 IAP RAS and RFNC-VNIIEF successfully implemented an ISTC project No. 223-95 entitled “The development of a high-speed technology for production of monosectorial water-soluble crystals”.
The co-executor of the Project is the RFNC-VNIIEF. This group participates in the investigations of nonlinear wave processes, in design, engineering and fabrication of separate units of experimental setups and models to be created; participates in experimental investigations and analysis of results obtained. The cooperators of this group participating in the project have substantial expertise in the development and creation of high power laser systems with radiation conversion into second harmonic on nonlinear KD*P crystals as well as in numerical modeling of wave processes and their experimental study. They are also experienced in the design of opto-electronic and opto-mechanical units of high power laser systems [6, 7, 12-16].
The Project mainly relates to basic research.
The Project will help implement a number of main objectives of ISTC:
- A large group of scientists and experts previously involved in defense-related activity will reorient their work to peace activity. Thirty-four arms scientists participate in the Project.
- A large amount of new important scientific information will be obtained. This information will be available for all concerned parties.
- The Project will facilitate integration of Russian scientists into the international scientific community. The Project will involve rich experience, methodology and material resources accumulated by participating institutions.
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