K. Burdonov

Laboratory unraveling of matter accretion in young stars

When matter accretes onto a young star, a shell of dense material can form around the impact, reducing its x-ray emission. Accretion dynamics in the formation of young stars is still a matter of debate because of limitations in observations and modeling. Through scaled laboratory experiments of collimated plasma accretion onto a solid in the presence of a magnetic field, we open a first window on this phenomenon by tracking, with spatial and temporal resolution, the dynamics of the system and simultaneously measuring multiband emissions. We observe in these experiments that matter, upon impact, is ejected laterally from the solid surface and then refocused by the magnetic field toward the incoming stream. This ejected matter forms a plasma shell that envelops the shocked core, reducing escaped x-ray emission. This finding demonstrates one possible structure reconciling current discrepancies between mass accretion rates derived from x-ray and optical observations, respectively.

Formation of a plasma with the determining role of radiative processes in thin foils irradiated by a pulse of the PEARL subpetawatt laser

A superbright X-ray source with a radiation temperature of ~1.2 keV making it possible to create a solid-state plasma whose kinetics is determined by the radiative processes has been implemented under the impact of a 170-TW pulse of the PEARL femtosecond laser facility on an aluminum target with submicron thickness. The diagnostics of the created plasma is performed by X-ray spectral methods using spectral transitions in hollow multicharged ions.

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.

Experimental evidence for short-pulse laser heating of solid-density target to high bulk temperatures

Heating efficiently solid-density, or even compressed, matter has been a long-sought goal in order to allow investigation of the properties of such state of matter of interest for various domains, e.g. astrophysics. High-power lasers, pinches, and more recently Free-Electron-Lasers (FELs) have been used in this respect. Here we show that by using the high-power, high-contrast “PEARL” laser (Institute of Applied Physics-Russian Academy of Science, Nizhny Novgorod, Russia) delivering 7.5 J in a 60 fs laser pulse, such coupling can be efficiently obtained, resulting in heating of a slab of solid-density Al of 0.8 µm thickness at a temperature of 300 eV, and with minimal density gradients. The characterization of the target heating is achieved combining X-ray spectrometry and measurement of the protons accelerated from the Al slab. The measured heating conditions are consistent with a three-temperatures model that simulates resistive and collisional heating of the bulk induced by the hot electrons. Such effective laser energy deposition is achieved owing to the intrinsic high contrast of the laser which results from the Optical Parametric Chirped Pulse Amplification technology it is based on, allowing to attain high target temperatures in a very compact manner, e.g. in comparison with large-scale FEL facilities.

Post-pulse generation effect in Q-switched lasers

We revealed experimentally the generation of a second giant pulse at the neighboring longitudinal mode in an Nd:YLF Q-switched laser and implemented new method of longitudinal mode selection based on this effect.

Using a multimode laser in interferometry of ultrasmall phase inhomogeneities

We describe a method for measuring the concentration of low-density gas jets with the aid of a multibeam optical interferometer. Sensitivity with respect to optical thickness distortions achieved in experiments was on a level of λ/600. The proposed method is well suited for the calibration of gas targets used in experiments on laser–plasma interactions.

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.

150MM diameter Nd:glass rod laser amplifier: characterization and prospects

We present the results of the investigation of a Nd:glass rod laser amplifier 320 mm long and 150 mm in diameter. The gain and depolarization distributions over the amplifier aperture as well as the stored energy have been measured for different values of the pump energy. The small signal gain averaged over the rod aperture was 2.3 when the pump energy was 48 kJ. The corresponding stored energy was 500 J. We have determined the maximal pulse repetition rate that is quiet safe from the point of the thermal shock damage. It is about 1 shot per 5 minutes. The calculated focal length of the thermal lens exceeds 1.5 km in such a regime. We have shown that the use of a couple of such amplifiers gives the possibility to increase the energy of laser pulses up to 650 J.