We have studied a laser diode self-injection locking to the modes of whispering gallery mode microresonator (WGMM) in a wide range of parameters and derived several regularities allowing optimization of the locking process. In this work we investigated in detail the optimization process, based on the thermal nonlinearity of the WGMM modes, when the laser frequency is tuned smoothly to the WGMM frequency (adiabatic tuning).
Lasing on 3p-3s transitions of neutral neon atoms upon pumping neon and its mixtures by a pulsed inductive discharge was obtained. The emission spectrum, depending on the pumping conditions, consisted of individual lines with wavelengths of 540.1,585.3, and 614.3 (594.4) nm.
We demonstrate experimentally that a sandwich-like structure comprising a thin layer of lithium niobate clamped between two Si prisms of total internal reflection can serve as an efficient converter of nJ-energy level laser pulses from a femtosecond optical oscillator to a high-quality beam of broadband terahertz radiation. The converter has an additional advantage of workability at different laser wavelengths.
The formation of binary amorphous-crystalline periodic structures on the surface of Ge2Sb2 Te5 thin film during a single pass of a femtosecond laser beam has been studied. We recorded biphase stripes up to several mm long consisted of 50 parallel amorphous/crystalline lines oriented perpendicular to the light polarization. These stripes had a period equal to the recording beam wavelength (1030 nm) and exhibited diffraction grating behavior due to the remarkable optical contrast. We performed diffraction simulations and obtained good agreement with the experimental results for a beam (532 nm) diffracted by the recorded grating.
An experimental and theoretical study of the processes occurring in the ytterbium-erbium doped fiber amplifier (YEDFA) has been carried out. Among them are up-conversion, energy-transfer, secondary energy-transfer (SET) processes. The introduced model makes it possible to analyze the amplification regimes of the amplifier and optimize YEDFA characteristics. While taking into account the SET process the calculation results demonstrated good agreement with experimental data in a wide range of input signal and pump powers.
Nonlinear effects are known to govern spectral properties of Raman fiber laser radiation well above the generation threshold, and the role of randomly distributed feedback in random fiber lasers is expected to be negligible. We numerically study spectral properties of a random fiber laser and a corresponding fiber amplifier with no feedback and emphasize the importance of Rayleigh backscattering.
We study the problem of third harmonic generation in a medium with combined quadratic and cubic nonlinear response under the condition of frequency doubling at big phase mismatching. Based on new analytical approach we found out the possibility of high frequency tripling conversion efficiency. This conclusion is supported by computer simulation results.
We propose a nanosphere array target in the plasma phase as an efficient dispersive medium for the intense XUV light originated from laser-plasma interactions where various high harmonic generation processes take place. The scattering process is studied with the help of numerical simulations using resonance conditions obtained from the analytical model. We show that the angular distribution of different harmonics after scattering can be good described by a simple interference, in particular for the rectangle symmetry the angular distribution corresponds to the Bragg-Wolfe diffraction theory.
We discuss the x-ray generation by electrons ac-celerated in the relativistic self-trapping regime of laser pulse propagation. It is shown that the secondary radiation has a high brightness. At the same time, this regime is accompanied by the particle interaction with a laser pulse that ensures partial polarization of synchrotron radiation and its nonisotropic angular distributions.
It is measured the kinetics of the luminescence of Fe2+ in ZnSe at liquid nitrogen temperature at excitation by short laser pulse with wavelength 2940 nm. It was showed that the form of luminescence decay curve depends on concentration of Fe2+. This was interpreted as a manifestation of concentration quenching of upper state of Fe2+.
Conventional Shack-Hartmann sensor uses Zernike polynomials for wavefront approximation. Each Zernike polynomial is orthogonal in the unit circle and describes specific aberration, e.g., defocus, coma, astigmatism, spherical aberration - that is one of the reasons why they are very popular in optics, ophthalmology and imaging applications. Zernike polynomials provide sufficient quality of approximation in case of circular beam aperture, but sometime fails in case of rectangular or ring-shaped apertures (the case considered in this paper). In this work we implemented the approach of the approximation of the wavefront using B-spline polynomials. We demonstrate that this approach is quite effective for non-circular light beam apertures. We present the results of approximation of the complex ring-shaped wavefront using B-Spline polynomials.
Consider bell-shaped functions as potentially new refractive index profiles of the fiber with low differential mode group delay. The Fermi-Dirac distribution and Cycloid functions are shown to provide twice or more the fiber-optic bandwidth compared to the conventional quasi-parabolic GRIN. The effect of refractive index fluctuations on the performance of these profiles is analyzed.
A generalisation of rate equations simulating donor-acceptor energy transfer and describing the time evolution of donors' and acceptors' luminescence power is proposed. These equations were supplemented by a time-dependent probability of the direct static disordered donor-acceptor energy transfer. A clear physical interpretation of the terms in the equations describing the various stages of the donor-acceptor energy transfer is given.
An increase in photoluminescence at a wavelength of $5\ \mu\mathrm{m}$ in glass-ceramics based on $\text{Tb}^{3+}$ -doped $\text{Ge}_{33}\text{Sb}_{3}\text{Ga}_{4}\text{Se}_{60}$ glass with nucleated and grown micro- and nanosized GeSe crystals is reported. Depending on the heat treatment temperature of the glass, an increase in luminescence by a factor of 1.5-4 is achieved. The mechanisms of luminescence enhancement and the influence of optical scattering losses on it are discussed.
The paper describes the proposed architecture of the optical interferometric system of the SOIGA project, and formulates the requirements for the properties of the main components. The results of the development of a ground model of a heterodyne interferometric system are presented, and the main sources of noise are evaluated. The sensitivity of the model of the interferometric system at the level of 100 pm is confirmed, ways of improving the model to achieve the required accuracy of several pm are shown. The results on the development of a system for guiding optical radiation between spacecraft are also presented.
The features of active laser delivery of modern chlorin-containing photosensitizing drugs under the nail plate and skin are discussed. The delivery was carried out by simultaneous microperforation of the nail plate and stimulation of laser-induced hydrodynamic processes in the drug applied to the nail surface. The optimal parameters for microporation and active laser delivery of drugs were determined. The results of studying the absorption spectra of modern chlorin-containing photosensitizing drug “Chloderm” in the range of 400÷900 nm before and after exposure to radiation with a wavelength of 450 nm, 654 ± 10 nm and 2810 nm are presented.
We present InAs-based quantum cascade lasers (QCLs) operating near 14 µm with a threshold current density as low as 630 A/cm 2 at room temperature, outperforming the best reported to date InP-based QCLs.
