S N Bagayev

New data on the physical properties of Y3Al5O12-based nanocrystalline laser ceramics

Microhardness and fracture toughness of highly transparent Y3Al5O12-and Y3Al5O12: Nd3+-based nanocrystalline ceramics are measured for the first time. For the Y3Al5O12: Nd3+ laser ceramics, the use of a longitudinal scheme with a diode-laser pumping at a wavelength of 1.3186 mm (4F3/2 → 4I13/2 channel) enabled one to attain an output power of continuous-wave lasing of ∼3.7 W with 35% efficiency.

High‐order stimulated Raman scattering combined with second harmonic generation in [χ(2)+χ(3)]‐nonlinear LaBGeO5, β′‐Gd2(MoO4)3 and Ca4Gd(BO3)3O laser host crystals under picosecond excitation

New frequency conversion processes leading to emission in the visible spectral range were observed for the first time by multiple Stokes and anti-Stokes Raman generation arising from intrinsic second harmonic generation in three different [χ(2)+χ(3)]-nonlinear LaBGeO5, β′-Gd2(MoO4)3 and Ca4Gd(BO3)3O laser host crystals under picosecond pumping at a fundamental wavelength of 1 μm.

The mode structure and spectral properties of supercontinuum emission from microstructure fibers

The mode structure and spectral properties of supercontinuum emission generated by femtosecond pulses of Ti: sapphire laser radiation in microstructure fibers are studied. The long-wavelength (720–900 nm) and visible (400–600 nm) parts of supercontinuum emission are shown to be spatially separated in microstructure-fiber modes, which can be isolated with an appropriate spectral filtering. The spatial modes thus isolated in spectrally sliced supercontinuum emission possess a spatial quality sufficient for further efficient frequency conversion. The possibility of achieving a high spectral quality of supercontinuum emission is also demonstrated. We explore the ways to control the spectrum of supercontinuum emission by matching parameters of the pump pulse with the parameters of a microstructure fiber and by tuning the initial chirp of the pump pulse. The results of our studies show that supercontinua produced in microstructure fibers offer new approaches to designing a new generation of optical parametric amplifiers and broadband radiation sources for spectroscopic, metrological, and biomedical applications.

Josephson dynamics for coupled polariton modes under the atom–field interaction in the cavity

We consider a new approach to the problem of Bose–Einstein condensation (BEC) of polaritons for atom–field interaction under the strong coupling regime in the cavity. We investigate the dynamics of two macroscopically populated polariton modes corresponding to the upper and lower branch energy states coupled via Kerr-like nonlinearity of atomic medium. We found out the dispersion relations for new type of collective excitations in the system under consideration. Various temporal regimes like linear (nonlinear) Josephson transition and/or Rabi oscillations, macroscopic quantum self-trapping (MQST) dynamics for population imbalance of polariton modes are predicted. We also examine the switching properties for time-averaged population imbalance depending on initial conditions, effective nonlinear parameter of atomic medium and kinetic energy of low-branch polaritons.

Femtosecond combs for precision metrology

A new stage of development of optical clocks and synthesizers is possible with the use of highly stable femtosecond lasers. Using femtosecond lasers and special optical fibres, a highly stable frequency comb covering the frequency interval up to several hundreds of THz with a spacing from 100 MHz to 1 GHz has been developed. Experimental schemes for the femtosecond optical clock based on the He-Ne/CH4 and Nd:YAG/I2 frequency standards are presented. The possibility of using tapered fibres for optical clocks and synthesizers is investigated. It is shown that, depending on their influence on the frequency characteristics of the spectral components of the transmitted radiation, tapered fibres can be used in femtosecond optical clocks and synthesizers.

Fabrication and Properties of Neodymium-Activated Yttrium Oxide Optical Ceramics

About new technology of production of transparent ceramics including laser synthesis of nanopowders, their magnetic pulsed compaction and vacuum sintering is reported. The results of investigations of the synthesized samples of transparent ceramics made from neodymium-activated yttrium oxide are presented. It has been shown that in a 1.1 mm thickness sample with optical loss coefficient α1.07μm = 0.03 cm−1 laser generation at λg ∼ 1.08 μm with a slope efficiency of 15% at laser diode pumping at a wavelength of 807 nm has been obtained.

Transformation of femtosecond Ti:S laser pulses by a tapered fibers

The method of the experiment consisted in the measurement of the stability of the intermode frequency of the Ti:S laser (100 MHz) at the input and output of the fiber. Besides, two spectral areas of output radiation were extracted with the help of light filters, and the stability of intermode beats in extracted spectral regions was measured. To make these high-precision measurements, we developed and created a device. This device is based on the following principle. The intermode frequency is transferred by transformation into the low-frequency region, and then high-precision measurements of the chosen frequency (200 Hz) are made. It is noted that at the passage of a sequence of highly stable femtosecond pulses through a tapered fiber in the process of nonlinear transformation of modes, there is some decrease in the intermode frequency stability

Formation and distortions of the ultrashort pulse train spectrum broadened in tapered fiber

We propose a theoretical description and give experimental results of the ultrashort pulse train spectral broadening in tapered fibers. A multi-peak spectral structure due to the effect of self-phase modulation was obtained. Phase and amplitude fluctuations were investigated. It is shown that stability of intermode beats remains after propagation through the tapered fiber.

The spectroscopy and lasing of monoclinic Tm:KY(WO{sub 4}){sub 2} crystals

The principal spectroscopic and lasing characteristics of a Tm(15%):KY(WO4)2 crystal were investigated. The transition cross sections, the luminescence quantum yield, and the lifetime and the nonlinear depopulation coefficient of the upper active state were also determined. The slope efficiency of lasing at the 1950 nm wavelength was 45%. The feasibility of tuning in the spectral range 1850 — 1950 nm was demonstrated in principle.

New nonlinear-laser properties of ferroelectric Nd{sup 3+}:Ba{sub 2}NaNb{sub 5}O{sub 15} - cw stimulated emission ({sup 4}F{sub 3/2} {yields} {sup 4}I{sub 11/2} and {sup 4}F{sub 3/2} {yields} {sup 4}I{sub 13/2} ), collinear and diffuse self-frequency doubling and summation

A new cw laser with self-frequency doubling and summation of 1-μm oscillation (4F3/2 → 4I11/2) was constructed on the basis of an orthorhombic Nd3+:Ba2NaNb5O15 crystal. The 4F3/2 → 4I13/2 inter-Stark transition was used to excite cw 1.3-μm stimulated emission from this ferroelectric.A new cw laser with self-frequency doubling and summation of 1-{mu}m oscillation ({sup 4}F{sub 3/2} {yields} {sup 4}I{sub 11/2}) was constructed on the basis of an orthorhombic Nd{sup 3+}:Ba{sub 2}NaNb{sub 5}O{sub 15} crystal. The {sup 4}F{sub 3/2} {yields} {sup 4}I{sub 13/2} inter-Stark transition was used to excite cw 1.3-{mu}m stimulated emission from this ferroelectric. (letters to the editor)