A. A. Kovalyov

High-power, efficient, semiconductor saturable absorber mode-locked Yb:KGW bulk laser.

A high-power, diode-pumped, semiconductor saturable absorber mode-locked Yb(5%):KGW bulk laser was demonstrated with high optical-to-optical efficiency. Average output power as high as 8.8 W with optical-to-optical efficiency of 37.5% was obtained for Nm-polarized laser output with 162 fs pulse duration and 142 nJ pulse energy at a pulse repetition frequency of 62 MHz. For Np polarization, 143 fs pulses with pulse energy of 139 nJ and average output power of up to 8.6 W with optical-to-optical efficiency of 31% were generated.

Semiconductor nanostructures modified by the UV laser radiation

The shortening of the absorption recovery time by a factor of more than 50 is observed for the semiconductor nanostructure consisting of ten GaAs/InxGa1-xAs/GaAs quantum wells irradiated with the nanosecond pulses of the XeCl laser.A possible reason for such a significant variation in the optical properties lies in the generation of point defects,which are responsible for recombination of charge carriers.The result can be employed in the UV photomodification of optical properties of semiconductor nanostructures.

A new technique to measure the phase characteristics of laser mirrors based on semiconductor heterostructures

A reflection interferometer based on a thin metal film is proposed to measure the phase of the reflection spectrum of laser mirrors. The device is applied to the study of the phase characteristics of the all-semiconductor mirror which combines the functions of the saturable absorber and the dispersion compensator (all-in-one) in the Nd3+:KGd(WO4)2 laser operating in the ultrashort-pulse regime. The method provides improvement of spectral resolutions and an increase in the accuracy in the measurement of the phase characteristics.

Yb3+:KY(WO4)2 laser with a fast saturable absorber

Quantum-well semiconductor structures with superlattice barriers and reduced recovery time of absorption are designed and manufactured. A saturable absorption mirror based on such a structure is used in the Yb3+:KY(WO4)2 laser. The mode locking at a repetition rate of 70 MHz yields an almost bandwidth-limited pulse with a duration of about 115 fs. The maximum mean power (1.57 W) is comparable with a CW power of 1.62 W, which indicates a relatively low level of nonsaturable loss in the saturable absorption mirror.

Coherent control of transient optical phenomena : Molecules, atoms, and nanostructures

The dynamic nature of the interaction between the electromagnetic field of radiation and a resonantly absorbing medium is manifested as Rabi oscillations and can substantially affect both stationary and transient optical processes. This effect was repeatedly demonstrated for nonstationary transient processes in gaseous media with homogeneously broadened absorption lines. A single approach to the coherent control of the transient processes in the media with essentially inhomogeneous broadening of the absorption line is proposed. The results of the study of the Doppler-broadened molecular transition are presented. The prospects for the study of alternative inhomogeneously broadened media (low-pressure atomic gas and the exciton transitions localized in quantum wells (nanosized semiconductor heterostructures)) are reviewed.

Fast mirrors for femtosecond passive mode-locked near-infrared lasers

The design, manufacturing and characterization of the near infrared fast, low non-saturable loss semiconductor mirrors with saturable absorption based on InGaAs quantum wells separated by super-lattice GaAs/InGaAs barriers are analyzed from the viewpoints of recovery time shortening mechanism and of further improvement of mirror performance.

Semiconductor A3B5 nanostructures for infrared femtosecond lasers

Two techniques were suggested and tested for the recovery time shortening of saturable absorbers on a base of A3B5 compounds including quantum wells. The first one, proposed by authors, is the sample post-growth treatment by UV laser radiation; it implied generation of point defects, which, in its turn, led to electron-hole recombination acceleration and to recovery time shortening by an order of magnitude and more. Another technique based on special design of barriers gave promising results for the fast saturable absorbers. Semiconductor mirrors designed for Yb3+:KY(WO4)2 infrared laser mode locking led to 115 fs stable mode-locking regime with average power close to CW operation. Results on fast saturable absorbers for spectral region of 1500 nm are also presented.

Reflectivity kinetics in the vicinity of exciton transitions in semiconductor nanostructures

The kinetics of the reflectivity of semiconductor samples with multiple GaAs/AlGaAs quantum wells has been investigated by the pump-probe method with a resolution of 150 fs. Excitons of the E1HH1 and E1LH1 types manifest themselves in the kinetics of transient reflectivity spectra despite the high density of the photogenerated two-dimensional electron gas. Differences are revealed in the shape and kinetics of the transient reflectivity spectra of samples with different detuning of exciton transitions from the pump frequency.

Detection peculiarities of coherent transients generated in molecular gas by Stark switching

Free polarization decay and photon echo were detected as heterodyne signals in the weak component of radiation, polarized at right angle to the principal part of exciting radiation. Coherent responses were generated in 13CH3F gas by Stark switching of molecular levels in a gas excited by CW CO2 laser radiation at 9P (32) line. The specific features of this technique in comparison with the conventional Stark switching method of coherent transients generation is considered.

Polarization properties of photon echo signals in ytterbium vapor: dependence on the area of exciting pulses

A brief review of theoretical predictions for photon echo polarization properties is presented from the viewpoint of their dependence eon the are of exciting pulses and on the contribution of depolarizing collisions. The choice of intercombination transition in ytterbium vapor as subject of investigation is explained. First experimental results on kinetics of resonant fluorescence at the transition of Yb (6s2