A A Kuzmin

Large-aperture Nd:glass laser amplifiers with high pulse repetition rate

Nd:glass amplifiers are used in most of the existed petawatt laser facilities. A typical repetition rate of such lasers is 1 shot per 30 minutes or less. Limitations are thermally induced distortions of radiation and tensile stresses in Nd:glass. An increase of the repetition rate is an urgent problem. We have investigated thermally induced depolarization and thermal lens effects in Nd:glass rods up to 10 cm in diameter at a pump pulse repetition period of 3 minutes. It is shown that the rods have a safety factor of at least 5 before thermal stress induced damage would occur, and despite of their size phase and polarization distortions could be compensated.

Neodymium glass laser with a phase conjugate mirror producing 220 J pulses at 0.02 Hz repetition rate

For pumping multipetawatt Ti:sapphire laser facilities we developed a compact repetitively pulsed laser based on neodymium phosphate glass with pulse energy of 220 J, pulse repetition rate of 0.02 Hz, beam diameter of 43 mm, aperture fill factor of 0.8, and FWHM pulse duration of 30 ns. The phase distortions of laser radiation were compensated by optical phase conjugation via stimulated Brillouin scattering. The depolarization was reduced to 0.4% using linear compensation methods. The beam quality was 2.5 x diffraction limit (150 µrad).

Simple method of measurement of phase distortions in laser amplifiers

Two alternative methods for determining phase distortions of radiation in the heated active element of a high-power Nd:glass laser are compared: direct phase measurement with the Mach–Zehnder interferometer and phase front reconstruction from measured distributions of depolarization factor. It is shown that the latter method can quite quickly and accurately determine the wavefront distortions of laser radiation with minimal interference to the optical scheme of the laser.

Experimental stand for studying the impact of laser-accelerated protons on biological objects

An original experimental stand is presented, aimed at studying the impact of high-energy protons, produced by the laser-plasma interaction at a petawatt power level, on biological objects. In the course of pilot experiments with the energy of laser-accelerated protons up to 25 MeV, the possibility is demonstrated of transferring doses up to 10 Gy to the object of study in a single shot with the magnetic separation of protons from parasitic X-ray radiation and fast electrons. The technique of irradiating the cell culture HeLa Kyoto and measuring the fraction of survived cells is developed. The ways of optimising the parameters of proton beams and the suitable methods of their separation with respect to energy and transporting to the studied living objects are discussed. The construction of the stand is intended for the improvement of laser technologies for hadron therapy of malignant neoplasms.

Nd : glass rod laser with an output energy of 500 J

The energy of two orthogonally polarised pulses injected into an available multistage amplifier based on neodymium phosphate glass rods was increased from 300 to 500 J (in both pulses). The second output pulse with an energy of 200 J will be used to pump an additional parametric amplifier of a petawatt laser.

Thermo-induced distortions of radiation in large aperture laser amplifiers

The depolarization dynamics in a neodymium glass rod laser amplifier is studied in experiments. A method for determining the temperature distribution and the thermally induced phase distortions by the known transverse depolarization degree distribution is proposed. The experimental results obtained by this method perfectly coincide with the theoretical data even at strong radial inhomogeneity of heat release.