Abstract
A time-dependent model of laser amplification in an Yb : YAG crystal is considered based on a system of balance equations, as well as radiation transfer and heat conduction equations. The ...model also takes into account the dependence of the laser characteristics of the gain medium on the injection wavelength and the effect of amplified spontaneous emission. This model is verified based on a diode-pumped amplifier with cryogenic cooling of active elements. The dependences of the gain on the pump pulse energy are experimentally measured for different amplification regimes and compared with simulation results.
A new original method has been developed and experimentally implemented, allowing temperature fields to be contactlessly measured in the pump region of active elements in high-power-diode-pumped ...laser amplifiers, including those operating at cryogenic temperatures. The presence of a temperature gradient of ∼57 K mm−1 along the pump beam axis at the centre of the active element of the laser amplification unit operating at cryogenic temperatures with a pulse repetition rate up to 1 kHz is simulated and experimentally confirmed.
A time-dependent three-dimensional model for the laser amplification process has been constructed with allowance for the effect of the temperature distribution on the thermophysical and lasing ...characteristics of gain media. We have performed numerical modelling of the laser amplification process in the gain elements of a two-stage subjoule-level cryogenic laser amplifier operating at a pulse repetition rate of up to 1 kHz. It has been shown that taking into account the temperature distribution is of critical importance in calculation of cryogenically cooled laser amplifiers pumped with high-power diodes. We have found optimal diode pump parameters at which the maximum achievable pulse energy at the amplifier output can reach 300 and 570 mJ at pulse repetition rates of 1000 and 500 Hz, respectively.
Artificial intelligence is stated to be more and more widely used in agriculture, as well as for the diagnostics of the agricultural machinery condition. It was noted that in besides software, new ...computing devices are developed that enable processing and storing large amounts of data. (Research purpose) To create a neural network-based software package for remote diagnostics of the limit state of machinery individual components and assemblies. (Materials and methods) Foreign studies within the problem area were analysed. It was found out that for data collection for artificial intelligence there exist STM32 and Arduino microcontroller-based devices, and the Nvidia CUDA (Compute Unified Device Architecture) hardware and software platform is used. For the software was developed in the C / C ++ programming language, and the MS SQL Server database were used as a repository. The general software is emphasized to be able to run on all major operating systems such as Windows, Mac OS, Linux. The role of neural network is argued to be important since it integrated all program blocks and provides its own analysis. (Results and discussion) The information from the diagnostics devices is accumulated in a database. The neural network created on the basis of this database is constantly learning and simultaneously analyzing incoming data in real time, automatically issuing its recommendations. It was found that the neural network created by the employees of the Federal Scientific Agroengineering Center VIM has more functional options, for example, it is able to work directly with devices and conduct a more detailed technical analysis. (Conclusions) A neural network for equipment condition diagnostics was created, which increases the efficiency of decision-making in case of repair, and improves forecast and predictability. The criteria for equipment operation were proposed.
Supercontinuum generation from the near to far IR during radiation filamentation in solid-state media in an anomalous dispersion region is theoretically investigated. The initial search for ...appropriate media with the use of an interference model showed that the widest IR spectrum is generated in media with high values of zero group velocity dispersion wavelength with the pump wavelength located not far from it. Halides belong to one of such media groups. The possibility of generation of a very wide supercontinuum in calcium fluoride (0.52–3.35 μm, which corresponds to 2.7 octaves), sodium chloride (0.7–7.6 μm, 3.5 octaves), and potassium iodide (0.66–22 μm, 5.1 octaves) is demonstrated by numerical simulation. Also, pulse self-compression down to 13 fs at the 5-μm central wavelength (about single period) has been observed in potassium iodide. The mechanisms of multi-octave supercontinuum generation are discussed.
In this article, we report on the fabrication and optical properties of highly transparent yttria ceramics for lasers active media with broadband gain profile. Laser synthesis method was used to ...produce Y2O3-based nanopowders doped with 1mol.% Nd3+ or Yb3+ for these transparent ceramics. The additives of sesquioxides Lu2O3 and Sc2O3 were used along with ZrO2 to disorder the crystalline structure. The porosity and average grain size decrease with these additives and the emission bandwidths of Nd3+ (4F3/2→4I11/2) and Yb3+ (2F5/2→2F7/2) transitions widen to 40 and 60nm, respectively. Laser operation with the slope efficiency of 29% was obtained in (Yb0.01Lu0.24Y0.75)2O30.88(ZrO2)0.12 ceramic sample.
Holders of the active elements of a multi-disk multipass amplifier with a liquid-free closed cryogenic cooling cycle are modified. The equilibrium temperature of the active elements is experimentally ...investigated in relation to the power of diode pumping for the modified crystal holders. The dependence of the gain coefficient on the temperature of the active elements is measured. A small-signal gain of up to 1.2 is obtained in a single pass through the active element.
The formation of luminescent colour centres in the LiF crystal under the action of femtosecond pulses of the first harmonic of a Ti : sapphire laser is experimentally studied. The experiments were ...carried out at low- and high-aperture focusing of radiation. The effect of both single pulses and multi-pulse trains on the crystals was studied. Channelling of laser radiation in the waveguides, induced by the filaments of the first pulses, is found. The multiphoton mechanism of interband absorption is confirmed. The optimal conditions of laser impact for designing luminescent emitters in the LiF crystal are determined.
Glasses of the TeO2-WO3-Yb2O3 system are synthesized for wide range of Yb3+ concentrations of up to 6.0 × 1021 ions/cm3. The spectral-luminescent properties of lightly doped samples are investigated ...at room temperature and at the boiling point of liquid nitrogen. The energies of the Stark levels of the ground and excited states of Yb3+ ions incorporated into tungsten–tellurite glass are determined by analyzing the low-temperature spectra. The absorption, emission, and gain cross section spectra are obtained. The excess of the measured fluorescence decay time over the radiative lifetime ∼0.3 ms derived from the absorption spectra is attributed to the reabsorption effect in bulk samples. Measurements of lightly doped glass powder in the immersion liquid are made to reduce the effect of reabsorption. The fluorescence decay time of the powder is very close to the calculated radiative lifetime. Compared with phosphate, silicate, and other Yb3+-doped glasses, the tungsten–tellurite glass has a promising potential as a gain medium for lasers and amplifiers.
•Absorption, emission, and gain cross section spectra were first obtained at 300 K and 77 K.•The Stark energies for Yb-doped tungsten–tellurite glass were first determined.•Lightly doped powder in immersion liquid provided decay time value very close to radiative lifetime.•The transparency intensity is assessed to be 0.86 kW/cm2.
The source of instabilities in the multidisk diode-pumped high power Yb:YAG laser amplifier with cryogenic closed-loop cooling in the laser amplification channel of the high-intensity laser system ...with 1 kHz repetition rate was determined. Dissected copper mounts were designed and used to suppress instabilities and to achieve repeatability of the system. The equilibrium temperature dependency of the active elements on average power was measured. The seed laser for the multidisk amplifier was numerically simulated and designed to allow one to increase pulses output energy after the amplifier up to 500 mJ.
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