We report an experimental study of broadband sum-frequency generation of a nonselective
Q
-switched CO laser (pulse duration, ~0.3 μs; repetition rate, ~90 Hz) in ZnGeP
2
crystals with and without an ...antireflective interference coating. The uncoated crystal surface is found to be optically damaged at a laser radiation intensity of 0.033 GW/cm
2
. Under the same conditions, no damage to the antireflection-coated surface of the crystal is observed. The maximum efficiency of broadband sum-frequency generation of the CO laser in the antireflection-coated sample is 4.8% and turns out to be two times higher than in the uncoated sample. The spectral characteristics of the radiation at sum frequencies do not change in using antireflection-coated and uncoated samples.
Broadband sum-frequency conversion of multiline (~ 60 spectral lines within ~ 5–6 μm wavelength interval) Q-switched CO laser emission in an AR-coated ZnGeP
2
crystal was experimentally studied by ...application of both single-pass and double-pass optical schemes. The maximum conversion efficiency in the double-pass scheme reached ~ 10% that is 2.5 times higher than one obtained in the same optical scheme with an uncoated ZnGeP
2
. The spectrum control of frequency converted radiation by changing angles of incident and reversed CO laser beams in the ZnGeP
2
crystal was implemented within the wavelength range from 2.52 μm up to 2.92 μm. The maximum spectrum width of 0.35 μm was obtained with the double-pass scheme when the angle of the laser beam incident on the crystal and the angle of the deflected reversed laser beam were −4.0° and 1.0°, respectively, the spectral bandwidth being three times broader than one obtained with the single-pass scheme.
A terahertz NH
3
laser optically pumped by “long” (~100 μs) pulses of an electron-beam-sustained-discharge CO
2
laser is demonstrated for the first time. The NH
3
laser pulses and the “long” pulses ...of the CO
2
laser are simultaneously measured with nanosecond resolution. The duration and the delay of the NH
3
laser pulse relative to the pump pulse are measured depending on the pulse energy of the pump CO
2
laser. The following emission wavelengths of the terahertz NH
3
laser were observed upon pumping by the 9R(30) line of the CO
2
laser: 67.2, 83.8, and 88.9 μm.
The artificial neuron proposed earlier for use in superconducting neural networks is experimentally studied. The fabricated sample is a single-junction interferometer, part of the circuit of which is ...shunted by an additional inductance, which is also used to generate an output signal. A technological process has been developed and tested to fabricate a neuron in the form of a multilayer thin-film structure over a thick superconducting screen. The transfer function of the fabricated sample, which contains sigmoid and linear components, is experimentally measured. A theoretical model is developed to describe the relation between input and output signals in a practical superconducting neuron. The derived equations are shown to approximate experimental curves at a high level of accuracy. The linear component of the transfer function is shown to be related to the direct transmission of an input signal to a measuring circuit. Possible ways for improving the design of the sigma neuron are considered.
The synthesis of hydrocarbons from dimethyl ether in an atmosphere of synthesis gas, over a Pd-Zn-HZSM-5/Al2O3 catalyst, under flow-circulation conditions, at a pressure of 10.0 MPa, was ...investigated. It was found that the resulting hydrocarbon fractions were characterized by a low concentration of aromatic compounds and high concentrations of iso- and cycloalkanes. The dependence of the yields of the main groups of products and individual components on the contact time was explained in terms of the occurrence of methylation, oligomerization, hydrogenation, H-transfer, and hydroisomerization reactions. The role of Pd and Zn in the formation of the products was evaluated.
•The catalyst for gasoline synthesis from DME with a low aromatic content is proposed.•Gasoline synthesis was investigated under flow-circulation conditions at 10.0 MPa.•Chemistry of gasoline synthesis was studied in a wide range of DME conversion.•The combination Pd and Zn over ZSM-5 demonstrates the synergistic effect.•The concentration of isoalkanes in gasoline is >70 wt%.
•High aspect-ratio holes drilling in polymethyl methacrylate by mid-IR lasers.•Waveguide structure formation in PMMA during laser drilling.•Comparison of results on PMMA processing by CO– and CO2– ...laser beam.
Experimental results on drilling of PMMA by mid-IR lasers are presented and discussed. Proper choice of a CO laser beam focusing conditions made it possible to produce high aspect ratio (∼100) holes. During the laser drilling a waveguide-like structure of the hole was formed in PMMA with almost a constant sub-millimeter diameter along its whole length. Characteristics of the holes drilled by CO laser (wavelength 5.0–5.5 µm) and CO2 laser (10.6 µm) beams are compared.
•Surface textures of austenite steel were produced by femtosecond laser.•One-dimensional nanograting and microrelief of various roughness have been received.•Ferrite (α-Fe) in the near-surface layers ...was formed in spallation regime.•Phases α-Fe, Fe3O4, γ-Fe2O3 in the near-surface layers were formed in the phase explosion regimes.•Heat-affected zone was observed in the high-fluence mode for phase explosion regime.
Topography, structure, and phase composition of surface layers of AISI 321 stainless steel textured by 1030-nm 320-fs-laser pulses were studied by scanning electron microscopy and X-ray diffraction analysis. Variation in single-pulse fluence and the number of pulses was found to change the laser-produced surface texture from one-dimensional quasi-periodic nanograting to microrelief of various roughness. It was shown that the nanograting formed in the spallation regime contained austenite, just as a non-irradiated steel surface, and ferrite. The redeposited oxide layers on the grating surface produced in the phase explosion regime with a thickness increasing versus single-pulse fluence were found to consist of austenite, ferrite, and Fe3O4. In case of high-fluence mode, the two-layer microporous oxide coating, consisting of Fe3O4 and Fe2O3 in addition to conventional phases, was detected. SEM studies showed that the submicrocrystalline structure of nano- and microsized ridges was preserved, except for the high-fluence mode.
•Broadband mid-IR laser based on frequency conversion in ZnGeP2 nonlinear crystal.•Frequency conversion efficiency of single-pass and double-pass schemes.•Spectral acceptance of a frequency convertor ...based on single-pass and double-pass scheme.•Spectral bandwidth extension in the double-pass scheme of a frequency convertor.
Broadband sum-frequency conversion of multiline Q-switched CO laser emission in a single uncoated ZnGeP2 crystal was experimentally studied by application of single-pass and double-pass optical schemes. The laser emitted sub-microsecond pulses of 4 kW peak power at 100 Hz pulse repetition rate on ∼60 spectral lines within ∼5–6 μm wavelength interval. The sum-frequency emission spectrum consisted of at least ∼100 spectral lines covering the wavelength interval of ∼2.5–2.9 μm. The double-pass scheme provided about 30% higher efficiency as compared to a traditional single-pass one, while the spectral bandwidth of frequency converted radiation was the same. Moreover, a feasibility of slight spectral bandwidth extension by a variation of a reverse beam direction was demonstrated for the double-pass scheme.
•Compact slab RF discharge CO laser with cryogenic cooling.•Fundamental and first overtone bands CO laser generation.•Q-switching in slab RF discharge laser.
A new repetitively pulsed cryogenically ...cooled slab RF discharge CO laser running in both fundamental and first-overtone bands without its active medium forced replacement with average output power three times as much as that of previous models was developed. Compared to our previous installations, the output power was increased due to using gold-coated copper electrodes of ∼ 1.5 times larger surface area. The fundamental band free-running lasing was obtained within the spectral range of 5.06–5.92 μm with average output up to ∼ 40 W. Under Q-switching the laser operated in the spectral range of 4.95–7.0 μm with pulsed peak power up to 4.5 kW. The first-overtone band lasing was observed in the spectral range of 2.6–3.05 μm with maximum average power of ∼ 6 W.
Directivity patterns of terahertz emission by femtosecond laser filament plasma in air after radiation propagation in hollow tubes with metal and dielectric (polypropylene) walls are experimentally ...studied. It is shown that narrow directed radiation can be obtained using quasi-waveguide propagation in a tube with dielectric walls, while the terahertz pulse duration is not affected significantly.
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