M. V. Petrenko

A study of vacuum-ultraviolet stability of silicon photodiodes

Silicon photodiodes have been tested for resistance to vacuum-ultraviolet radiation at 121.6 nm. The responsivities of the p-n and n-p photodiodes under study were found to degrade by tens of percent at a VUV radiation dose on the order of tens of mJ/cm2. The effect of reversible photocurrent relaxation has been observed in detectors based on n-p structures.

Shock waves in gas-jet target of a laser-produced-plasma short-wave-radiation source with two-pulse plasma excitation

Previous investigations of the laser plasma at two-pulse mode of its generation revealed long-living perturbations of the gas-jet target by the first pulse, leading to significant modulations of the plasma radiation. In the present paper, results of a numerical hydrodynamic simulation of the gas-jet target are reported which provide explanation of the observed phenomena. An impact of the first pulse (prepulse) upon the target results in formation of a dense quasi-spherical layer in it, with a low-density area inside. This layer expands with the time and drifts downstream with the gas flow. Depending on the time interval between pulses, the second laser pulse can either intersect the dense layer or pass through the low-density gas, whereby the observed modulations of the plasma emission can be explained.

Laser spark propagation along the beam in stationary gases at low pressures

A study of space-time evolution of the laser spark induced with the Nd: YAG laser in stationary gases at low pressures has been realized with the aid of high-speed photography. A mechanism to explain light propagation along the beam is proposed. Calculated data are in a good agreement with the experimental ones. The article was translated by the authors.

Start-phase ionization dynamics in the laser plasma at low gas target densities

In Xe laser-produced-plasma sources of short-wave radiation, the laser-energy-to-EUV conversion efficiency (CE) proves substantially less than theoretical expectations. In the present work, a calculated estimate has been made which indicates that a long period of the primary ionization, lasting up to a moment when high-Z ions appear to emit short-wave photons, can be one of main causes for this. During that period the plasma remains low-ionized and absorbs weakly the laser energy. The estimate above has been experimentally confirmed with spectroscopic data and those on the effective ion charge derived from measured absorption of the laser radiation in the plasma. A preionization of the gas target with an ultraviolet (UV) excimer laser pulse is proposed as a method to accelerate the ionization process and consequently, to enhance CE.

Ionization dynamics in the laser plasma in a low pressure gas target

In Xe-laser-plasma short-wave-radiation sources, the laser-energy-to-EUV conversion efficiency (CE) turns out to be substantially lower than theoretical expectations. An estimation made in the present work is evidence of what a long period of the primary ionization, lasting up to a moment when high-Z ions appear to emit short-wave photons, can be considered as a main cause for the low CE values. During that period the plasma remains low-ionized and absorbs weakly the laser energy. Data deduced from laser light absorption measurements confirm the estimation above. A preionization of the gas target with the UV excimer laser pulse is proposed as a method to accelerate the ionization process.

A study of the laser plasma in stationary gases at low pressures

Stretched along the laser beam and symmetrical relative to the focus forms of the laser spark induced with the Nd:YAG laser have been observed in stationary gases at low pressures. The spark length rose as the gas pressure increased amounting up to several millimeters. Based on shock waves, conventional mechanism of laser plasma propagation along the beam has been placed in question. Plasma temperature has been deduced from laser energy absorption in the plasma.

A new method for determining the efficiency of laser radiation conversion into 13.5 ± 0.3 nm radiation in laser-plasma extreme ultraviolet sources

We have studied extreme ultraviolet (EUV) emission from a laser-plasma source employing a supersonic xenon jet as the target. The output EUV energy has been determined as a function of the laser pulse energy for the supersonic xenon jet in comparison to the solid metal (Cu, Mo, Ta) targets. Based on these results, a new method for determining the efficiency of laser radiation conversion into EUV radiation is proposed, which ensures unambiguous characterization of the properties of various targets. Ways to optimize the xenon jet source are discussed.

Photoresponse of a Silicon Multipixel Photon Counter in the Vacuum Ultraviolet Range

Photoresponse of a silicon multipixel photon counter (MPPC) operating in the Geiger breakdown regime has been studied at wavelengths λ = 115, 121, 128, 160, and 175 nm. It is established that radiation intensity at these wavelengths can be measured by MPPC at room temperature in the photon-count mode with efficiency on a level of 2%.

Compact spectrometer for 5–30 nm wavelength range

The optical scheme of a compact spectrometer for a 5–30 nm wavelength range has been developed and a prototype instrument has been designed, constructed and tested. Small dimensions of the spectrometer and its short distance (34 mm) from the radiation source allow the spectrometer to be used inside small vacuum chambers with “point” radiation sources (laser plasma, etc) for studying their spectral compositions and intensities.

Features of experimental spectra of the laser plasma with a dense xenon gas-jet target in the extreme ultraviolet range

Emission spectra in the wavelength range of 5–25 nm of the laser plasma produced using a gas jet of Xe and a mixture of Xe + Ar with an atomic density of up to 7 × 1018 cm–3 are described. There are no discrete spectral lines in the xenon spectra, but a wide continuous peak of the radiation is observed within the 9–14 nm wavelength band. At variations of experimental conditions, its maximum demonstrates a regular wavelength shift, which is attributed to the corresponding change in the plasma temperature. Another feature is an only slight decrease in the intensity of xenon emission when the target is strongly diluted with argon.