•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.
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.
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.
•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.
The research studies of e-beam sustained discharge gas lasers initiated by Nikolai Basov in early 1970s made it possible to develop lasers based on the fundamental transitions of carbon monoxide ...molecule with high laser power and efficiency. Soon, under his scientific supervision, lasing on first-overtone transitions of CO molecule was obtained. Following these results, about ten years ago a compact slab CO laser excited by a repetitively pulsed capacitive RF discharge and cryogenic cooling of its electrodes, operating without forced pumping of its active medium was for the first time developed at the N.G. Basov Quantum Radiophysics Division of the P.N. Lebedev Physical Institute. At present, the average power of such lasers with active medium volume of ~ 35 cm
3
reaches 40 W on CO molecule fundamental transitions (in the wavelength range of 5.06–5.92 μm) and 6 W on first-overtone transitions (λ = 2.60–3.05 μm). Under Q-switching, those repetitively pulsed lasers allow one to obtain laser emission with a peak power up to 5 kW which made it possible to apply them in experiments on laser radiation frequency conversion in nonlinear crystals into the spectral range of ~ 2–20 μm.
•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.
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.
In this work the formation of laser-induced periodic surface structures (LIPSS) on a titanium surface upon irradiation by linearly polarized femtosecond (fs) laser pulses with a repetition rate of 1 ...kHz in air environment was studied experimentally. In particular, the dependence of high-spatial-frequency-LIPSS (HSFL) characteristics on various laser parameters: fluence, pulse number, wavelength (800 nm and 400 nm), pulse duration (10 fs - 550 fs), and polarization was studied in detail. In comparison with low-spatial-frequency-LIPSS (LSFL), the HSFL emerge at a much lower fluence with orientation perpendicular to the ridges of the LSFL. It was observed that these two types of LIPSS demonstrate different fluence, shot number and wavelength dependencies, which suggest their origin is different. Therefore, the HSFL formation mechanism cannot be described by the widely accepted interference model developed for describing LSFL formation.
This publication discusses the mechanisms underlying the development of arterial hypertension on the background of stress, discusses the current problems of blood pressure control in patients with ...stress-induced sleep disorders, the clinical features of patients with hypersympathicotonia as the main mechanism for the development of arterial hypertension and blood pressure variability in patients with comorbid pathology, a diagnostic algorithm, as well as presenting current recommendations in the strategy for choosing the optimal antihypertensive therapy with the possibility of personalized choice in various clinical situations.
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•Laser ablation of Si was performed both in air and water environments at different fleunces and variable pulsewidths.•Only shallow spallation occurred in air for 10-ps laser pulses, ...comparing to spallation and phase explosion for shorter pulses.•Shallow laser ablation occurred in water at supercritical peak pulse powers due to laser beam self-focusing and filamentation.•Intense, phase explosion-like ablation takes place during wet ablation by 10-ps laser pulses at sub-critical peak pulse powers.
Comparative single-shot pulse study of ablation topographies and depths on Si surfaces excited by 1030-nm sub- (0.3 ps) and pico-picosecond (10 ps) laser pulses at different laser fluences in air and water environments was performed. Fast energy transport via 3D-diffusion of dense electron-hole plasma was revealed at picosecond timescale to extend transversely the ablation craters over the focal spot in air for laser pulse widths shorter, than electron–phonon thermalization time about 3 ps. In the given fluence range fluence-independent shallow ablation was observed in air for 10-ps pulses. Then, rather shallow laser ablation occurred in water at supercritical peak pulse powers, apparently, due to laser beam deterioration by self-focusing and filamentation. Finally, very intense, fluence-dependent material removal took place during wet ablation by 10-ps laser pulses at the sub-critical peak pulse powers. Electron-hole plasma and related energy transport on Si surface, 1030-nm laser pulse filamentation in water, pulsewidth and ambient medium effects were revealed during the surface ablation studies.
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