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Quantum cascade lasers, whose wavelengths collectively range from 3 µm to 25 µm and beyond, can now be stabilized in frequency to better than 1 part in 10{sup 14}.
Different versions of optical parametric oscillator (OPO) schemes were experimentally realised and investigated, which utilise AgGaS{sub 2}, LiNbO{sub 3} and HgGa{sub 2}S{sub 4} single crystals as well as an Hg{sub 1-x}Cd{sub x}Ga{sub 2}S{sub 4} solid solution. The OPOs generate radiation in the 1.2-5.7-{mu}m range and make use of different ways of output wavelength tuning, including fast wavelength tuning (in a time shorter than 0.1 ms) with the help of an acoustooptical deflector. The output spectral line was narrowed by means of an intracavity acoustooptical filter. An OPO for the visible range with an electrodynamic tuning to an arbitrary wavelength in this range in a time of 5ms was implemented employing a BBO single crystal. (invited paper)
We have prepared {sup 28}Si, {sup 29}Si and {sup 30}Si single crystals with enrichments above 99.9 at % and a silicon single crystal of natural isotopic composition. The oxygen and carbon concentrations in all the crystals are within 5x10{sup 15} cm{sup -3}, and the content of metal impurities is 0.01 - 0.1 ppma. The refractive index of the crystals has been determined in the range 1.05-25.5 {mu}m using interference refractometry, and its dispersion and material dispersion have been determined. (letters)
Tellurium-doped germanosilicate fibre has been fabricated by the MCVD process. In contrast to Te-containing glasses studied earlier, it has a broad luminescence band (full width at half maximum of {approx}350 nm) centred at 1500 nm, with a lifetime of {approx}2 {mu}s. The luminescence of the fibre has been studied before and after gamma irradiation in a {sup 60}Co source to 309 and 992 kGy. The irradiation produced a luminescence band around 1100 nm, with a full width at half maximum of {approx}400 nm and lifetime of {approx}5 {mu}s. (letters)
The first fibre preforms with a Pb-doped silica core, free of other dopants, have been produced using chemical vapour deposition. The preforms have been used to fabricate holey optical fibres. The spectroscopic properties of the fibres have been studied in detail in the range 400 - 1700 nm: we have measured the optical loss, constructed a three-dimensional luminescence excitation - emission graph and determined the decay time for the major luminescence peaks.
We report a single-frequency sub-nanosecond optical parametric oscillator (OPO) based on periodically poled stoichiometric lithium tantalate (PPSLT), pumped by a 1064-nm amplified microchip laser at a repetition rate of 0.5 kHz. Using a 11-mm-long PPSLT crystal polled with three different domain periods (30.2, 30.3, 30.4 {mu}m) and changing the temperature of the crystal from 20 Degree-Sign C to 265 Degree-Sign C, we have achieved wavelength tuning between 2990 nm and 3500 nm. The high nonlinearity of the used medium and the large aperture (2 mm) ensure the maximum idler output energy of {approx}0.5 mJ in the whole tuning range, corresponding to average {approx}10.5 % idler conversion efficiency and {approx}250 mW of average power. Sub-nanosecond pulse durations have been obtained for the idler at 0.88-ns pulse duration of the pump.
Lasing properties of a-cut Nd : YVO{sub 4} - YVO{sub 4} composite vanadate crystals are experimentally studied for the {pi} and {sigma} polarisations of radiation at the {sup 4}F{sub 3/2} - {sup 4}I{sub 11/2} transition. Polarisation dependences of the lasing characteristics of passively Q-switched Nd : YVO{sub 4} - YVO{sub 4} lasers with Cr{sup 4+} : YAG Q-switches are investigated. It is shown that the laser operates with the highest efficiency in the case of the {sigma}-polarised radiation (minimum pulse duration shorter than 1.5 ns, maximum peak power up to 25 kW, maximum peak energy about 35 {mu}J at a slope efficiency up to 32 %). Frequency conversion to the second and fourth harmonics is demonstrated. Based on this study, a multiwavelength laser with bactericidal and therapeutic effects is developed for treatment of a wide spectrum of diseases.
This paper presents an experimental study of quantum well superluminescent diodes with an extremely thin (InGa)As active layer. Under cw injection, the output power of such diodes is several milliwatts, with a centre wavelength of 830 nm and emission bandwidth of about 100 nm. (letters)
We have studied temporal and amplitude characteristics of the electrical signal arising under irradiation of the free water surface by a 2.94-{mu}m high-power laser. The investigations have been conducted using a specially designed electrode system, which makes it possible to record the motion of the electric charge after the end of the laser pulse. We have measured the dependences of the signal parameters on the radiation energy density at the water surface. (interaction of laser radiation with matter)
We have studied the optical properties of lightly bismuth doped ({<=}0.002 mol %) germanate glasses prepared in an alumina crucible. The glasses are shown to contain bismuth-related active centres that have been identified previously only in bismuth-doped fibres produced by MCVD. With increasing bismuth concentration in the glasses, their luminescence spectra change markedly, which is attributable to interaction between individual bismuth centres. (optical fibres)
A model of optical nonlinearity of air (atmospheric nitrogen and oxygen) is developed. This model can be used to calculate numerically the propagation of radiation with a wavelength close to 10 μm. It takes into account the electronic Kerr effect, higher order nonlinearities, ionisation of a gas medium by electron impact, and pulse group-velocity dispersion. The applicability limits of the Drude approximation for calculating the impact-ionisation rate are also considered. (nonlinear optical phenomena)
The pump wavelength of parametric amplifiers based on CLBO, DCDA and LBO crystals and pumped by the second harmonic of a femtosecond Cr : forsterite laser (620 nm) is close to optimal for broadband amplification because of the proximity of group velocities of interacting pulses. Injection of a broadband continuum into the range of the signal-wave gain in LBO and DCDA parametric amplifiers, pumped at λ = 620 nm, leads to generation of broadband femtosecond pulses with a spectrum ranging from 1050 to 1600 nm and peak powers up to 20 MW. (nonlinear optical phenomena)
A series of light-emitting modules based on single-mode quantum-well superluminescent diodes with centre emission wavelengths of about 790, 840, 960 and 1060 nm and a cw output power up to 100 mW in free space is developed. A sufficiently long service life of these devices is demonstrated. (lasers)
It is shown that in resistive Ag/Pd films manufactured according to the thick-film technology, in the case of oblique incidence of laser radiation of nanosecond duration at a wavelengths of 1350 – 2100 nm, a photon-drag photocurrent arises in the direction perpendicular to the plane of incidence, dependent on the ellipticity and sign of circular polarisation of incident radiation. This photocurrent consists of the so-called circular and linear contributions, which are, respectively, dependent on and independent of the sign of circular polarisation. In this wavelength range, the amplitude of the circular contribution is many times greater than that of the linear contribution. The results allow the use of resistive Ag/Pd films for the development and manufacture of innovative sensors of the sign of circular polarisation of pulsed laser radiation, operating in a wide spectral range. (interaction of laser radiation with matter. laser plasma)
We have developed two new types of lasers based on quantum-confined semiconductor optical amplifiers with an acousto-optic tunable filter in an external fibre ring cavity. The lasers offer continuous wavelength tuning ranges from 780 to 885 and from 880 to 1010 nm, 20 mW of cw output power, and a tuning rate up to 10{sup 4} nm s{sup -1} at an instantaneous spectral linewidth less than 0.1 nm. (lasers)
The propagation of N-soliton pulses in an optical fibre with slowly decreasing, shifted anomalous dispersion has been studied experimentally and theoretically. Using a generalised nonlinear Schrödinger equation, we have constructed an adequate numerical model for light propagation in such fibre. Using numerical simulation, we have shown that the use of dispersion-decreasing fibres ensures higher average dispersive radiation intensity and better uniformity of the supercontinuum spectrum. A reduction in the third-order dispersion of such fibres enables supercontinuum generation with a bandwidth exceeding that in homogeneous fibres by several hundred nanometres even in the case of a medium-power subpicosecond source. (nonlinear optical phenomena)
The parametric generation in a nonlinear PPLN crystal synchronously pumped by a Q-switched mode-locked Nd : YAG laser with a pulse duration of 45 ps is studied. The output pump intensity in the nonlinear crystal reaches ∼10 GW cm{sup -2}. At a pulse repetition rate of 1 kHz, the average output power at the idler wavelength (∼3.6 μm) is ∼12 mW, the peak power is ∼25 kW, and the conversion efficiency (with respect to the absorbed power) is ∼10%. The radiation linewidth at the signal wavelength (∼1.5 μm) is 13 cm{sup -1}. Along with the signal and idler waves, the output emission spectrum contains lines at wavelengths of 822, 754, 624, 532, 463, 442, 392 and 355 nm. The tunable radiation with wavelengths in the vicinity of 392, 463 and 822 nm is observed for the first time. The tuning ranges for the new lines are measured (5 – 10 nm) and their origin is explained. (nonlinear optical phenomena)
We have studied the luminescence properties of optical fibres with a bismuth-doped alumino- and phosphosilicate glass core under two-step excitation and obtained new experimental data on the properties of luminescence centres in such fibres. (fiber optics)