Pulse-Repetition in the yag:Nd Laser System as a Source of Soft X-rays pra-0073

Full Title Powerful Pulse-Repetition in the YAG:Nd Laser System for Laser-Plasma as a Source of Soft X-rays Tech Area / Field

PHY-OPL: Physics / Optics and Lasers

Brief Description of Technology At present in developed countries, a demand is growing for pulse-repetition YAG:Nd lasers that can be applied in various fields of science, including laser technology and medicine. Lasers can be designed to have certain radiation parameters corresponding to their scope. However, as a rule, pulse-repetition YAG:Nd lasers do not combine high averages and peak radiation powers with diffraction divergence nor, consequently, high laser beam intensity at its focus. Such a laser may be used in a laser-plasma radiation source of soft X-rays (=1-5 nm). In this case, the target should have the intensity of J = 10¹³ - 510¹⁴ W/cm². In the pulse-repetition regime, for example, such high intensity may be obtained in a pulse with a duration of 1-2 ns, and with an energy of E = 1-2 J. It is also known that the process of conversion of the laser beam energy into soft X-ray radiation occurs more effectively at the second harmonic, as opposed to the first. The aim of the proposed project is to design a laboratory compact pulse-repetition YAG:Nd laser with high peak and average powers, diffraction output beam divergence and effective conversion (>50 percent) to the second harmonic (=532 nm). The pulse energy at the fundamental frequency (=1064 nm) is E = 1.8-2 J, the pulse duration 1-2 ns and the repetition rate up to 15 Hz. The design of the proposed laser is based on our developments [1-6] of powerful pulse-repetition YAG:Nd lasers with the use of phase conjugation (PC) via SBS. In this project we plan to develop a stable master oscillator with an output radiation pulse duration of 3-5 ns and an energy of 3-5 mJ in one longitudinal, and one transverse mode. Having passed the system of spatial beam shaping (a telescope with a space filter and an apodizing diaphragm), the laser beam passes through the Faraday isolator and arrives at the four-pass amplifier. The amplifier is based on two wide-aperture effective amplifier heads with YAG:Nd crystals 15 mm diameter. The length of the illuminated region is 90 mm. (The Faraday isolator, using permanent magnets and wide-aperture amplifying heads, is developed by the team of authors in IAP RAS). After the second pass through the amplifier the beam is directed to the SBS-mirror, where PC and partial pulse compression take place. During the third and fourth passes, the pulse is amplified up to an energy of 1.8-2 J, and decreased to up to 1-2 ns. Owing to PC the beam has a diffraction divergence at the output. Thus, the radiation of the fundamental frequency will have the intensity of about 1 GW/cm² in the beam (diameter 13.5 mm at level 1/e) with diffraction divergence. Calculations and experimental results [1,2] show that this radiation should convert to the second harmonic with an efficiency of about 50 percent. The analysis of related publications shows that only we have the priority in developing similar powerful pulse-repetition YAG:Nd lasers. Having performed considerable research in this field, we hope to fulfill this project successfully.

Legal Aspects We have no patents.

Special Facilities in Use and Their Specifications The proposed design of the laser also permits the output radiation with a pulse duration in the range of 1-15 ns, and an energy output of 1.8-2 J in the beam with diffraction divergence.

Scientific Papers 1. N.F. Andreev, N.G. Bondarenko, I.V. Eremina, S.V. Kuznetsov, O. Palachov, G. Pasmanik, E. Khazanov. “A single-mode YAG:Nd laser with an SBS mirror and conversion of the radiation to the second and forth harmonics.” Sov. J Quant. Electr., 18, 10,1154-1160.

2. N. Andreev, A. Babin, E. Khazanov, S. Papernyi, G. Pasmanik "Pulse-repetition solid-state laser with SBS-ctlls." Laser Physycs, 2, 1, 1-19 (1992).

3. N. Andreev, E. Khazanov, G. Pasmanik "Applications of Brillouin cell to high repetition rate solid-state lasers." IEEE J. Q.E., 28, 1, 330-342 (1992).

4. N.F. Andreev, S.V. Kuznetsov, O. Palachov, G. Pasmanik, E. Khazanov. “Four-pass YAG:Nd laser amplifier with compensation for aberration and polarization distortion of the wavefront.” Sov. J Quant. Electr., 19, 9, 862-864 (1992).

5. N. Andreev, E. Khazanov, A. Kocherov, A. Matveev, O. Palachov, G. Pasmanik "Phase conjugation to upgrade efficiency of solid-state laser energy conversion to narrow-band TEM00 mode pulses." IEEE J Q.E.,v. 30, 2, 305-313 (1994).

6. N.F. Andreev, O. Palachov, G. Pasmanik, E. Khazanov. “Four-pass YAG:Nd laser system with compensation for aberration and polarization distortion of the wavefront.” Sov. J Quant. Electr , 23, 1, 21-24 (1996).