Q-switch pumped InSb spin-flip raman laser action under pulsed electric field conditions

Temporal synchronization of a Q-switch spin-flip Raman laser pulse (SFR) with a voltage pulse across an InSb sample leads to an enhancement of the Stokes output and to a shortening of the spin-flip pulse duration. During the end of the voltage pulse with a fall time ? 30 ns, the Stokes output power increased by a factor 2–3 while the SFR pulse duration decreased to 50 ns.     

Raman gain,effectiveg-value and spontaneous spin-flip Raman linewidth in Hg0.77Cd0.23Te

We report on measurements of spin-flip Raman gain inn-Hg_1?x Cd _x Te (x=0.23, carrier density 1.0×10¹⁵cm^?3) as a function of the magnetic field up to 1.6T. The measurements were carried out by a small signal gain technique at a temperature of 1.8 K. Furthermore, the measurements yield lineshapes and linewidths of the spontaneous scattering and allow a precise determination of the effectiveg-value. The highest gain observed is 0.2 cm/W. The band edge value of the effectiveg-value is ?93.2 and the widths of the symmetric lines are between 18 and 120 G, depending on the magnetic field.     

Raman-gain, linewidth, and effective g -value with spin-flip-Raman scattering in inSb

In this paper we report on measurements of spin-flip-Raman gain inn-InSb as a function of the magnetic field. The measurements were carried out at temperatures of 1.8 K and 4.2 K and at a carrier concentration of 1.35×10¹⁵ cm⁻³. The Raman cross sections obtained from these results, e.g. 1.25×10⁻²⁰ cm²/sr at a magnetic field of 10 kG and a pump frequency of 1884.35 cm⁻¹, agree very well with those theoretically predicted by Wherrett and Wolland. Furthermore, these measurements yield line shapes and linewidths of the spontaneous scattering (100–1500 MHz) and allow the determination of the effectiveg-value with an accuracy known from ESR-investigations. These results are discussed in terms of already published theoretical investigations.     

Electronic states and interband light absorption in semi-spherical quantum dot under the influence of strong magnetic field

In the framework of effective mass approximation the electronic states in semi-spherical quantum lens under the influence of strong magnetic field are investigated. We have used the adiabatic approximation for the case of strong magnetic field. The eigenfunctions and eigenvalues of this problem are determined. In strong confinement regime interband optical absorption of light is investigated in quantum lens from InAs. The threshold frequencies of absorption are determined. The comparison with the case of film under the influence of strong magnetic field with infinitely high confinement potential is performed.     

On the interaction of stimulated spin-flip raman scattering and stimulated recombination radiation in InSb

We have studied the interaction of stimulated spin-flip Raman scattering and stimulated recombination radiation in n-InSb using a CW CO pump laser. A change in linewidth and output power of second Stokes spin-flip radiation is observed when the tuning curve of the first Stokes stimulated spin-flip radiation and the stimulated recombination radiation cross. The observations are explained using a simple rate equation model.     

Steady-state and transient Raman gain in magnetoactive narrow band-gap semiconductors

Using the hydrodynamic model of semiconductor-plasmas and following the coupled-mode approach, a detailed analytical investigation is undertaken to study both steady-state and the transient Raman gain in transversely magnetized narrow band-gap semiconductors arising from electron density perturbations and molecular vibrations of the medium. Using the fact that the origin of stimulated Raman scattering (SRS) lies in the third-order susceptibility of the medium, we obtain an expression for the gain coefficient of the backward Stokes mode in steady-state and transient regimes and study the dependence of the magnetic field and pump pulse duration on its growth rate. The threshold pump intensity and optimum pulse duration for the onset of transient SRS are estimated. An externally applied magnetic field substantially enhances the transient SRS gain coefficient in narrow band-gap semiconductors, which can be of great use in the compression of scattered pulses.     

Laser field effect on the nonlinear optical properties of a square quantum well under the applied electric field

In this paper the effect of the laser field on the nonlinear optical properties of a square quantum well under the applied electric field is investigated theoretically. The calculations are performed in saturation limit using the density matrix formalism and the effective mass approach. Our results show that the laser field considerably effects the confining potential of the quantum well and thus the nonlinear optical properties.     

Artifacts in femtosecond transient absorption spectroscopy

The paper discusses three different artifacts related to two-photon absorption (TPA), stimulated Raman amplification (SRA) and cross-phase modulation (XPM), all intrinsic to transient absorption measurements with femtosecond time resolution. Certain properties of these signals are analysed and shown to superimpose onto measured transient absorption spectra. Ways of reducing the influence of the artifacts discussed are suggested. A simple correcting procedure based on the linear intensity dependence of the artifacts discussed is proposed. Received: 29 May 2001 / Final version: 15 October 2001 / Published online: 29 November 2001     

Anti-ferromagnetic ordering and crystal electric field in Ce:GSAG and Ce:LLGG garnets

The magnetic susceptibility of Ce:Gd₃Sc₃Al₃O₁₂ (Ce:GSAG) and Ce:La₃Lu₂Ga₃O₁₂ (Ce:LLGG) has been studied in the temperature range from 15 to 293 K. Both the Ce-doped garnets Ce:GSAG and Ce:LLGG show anti-ferromagnetic ordering at 18 and 27 K, respectively. Crystal electric field split energy levels have been used to calculate the magnetic susceptibility following Van Vleck's model. The calculated susceptibility values reasonably agree with the experimental susceptibility data of Ce:LLGG but differ for that of Ce:GSAG system. Contribution from long-range ordering between Ce and Gd ions for anomaly in Ce:GSAG system is speculated.     

Determination of temperature by stimulated raman scattering of molecular nitrogen,oxygen, and carbon dioxide

We have determined the temperature from SRS spectra of N₂-N₂, N₂-CO₂, O₂-O₂, and CO₂-CO₂ recorded in wide pressure and temperature ranges. The fitting procedure takes simultaneously into account the Dicke effect and motional narrowing. We have quantified the accuracy of the MEG and ECS-P models for rotational relaxation. The temperature extracted from each model is compared with thermocouple measurements. The influence of vibrational broadening and shifting is discussed in detail.     

Coherent raman spectroscopy of nitrogen molecules and clusters in supersonic jets

Coherent Stokes and anti-Stokes Raman scattering CSRS and CARS have been employed to study the spectroscopy of nitrogen molecules and clusters in the expansion of a supersonic jet. In the vibrational spectrum, at strong stagnation conditions, an intense redshifted peak is observed which can be assigned to the intramolecular vibrations in large N₂ clusters having adopted the -phase structure. Another weak feature is assigned to nitrogen clusters in the -phase. In the rotational region of the spectrum only monomer features have been observed. The failing to observe librational motions is consistent with the finding that the nitrogen clusters are predominantly in the orientationally unordered -phase. The low rotational temperature suggests supercooling of the -phase.     

The role of the longitudinal component of the electric field vector in two-wave mixing in photorefractive BaTiO3

It is shown that for waves incident with a polarisation in the plane of the grating the component of the electric field in the direction of propagation must be included in the calculations. Coupled differential equations for both the transverse and longitudinal components are derived for wave interaction in photorefractive BaTiO₃. Analytic solutions for the electric field of the signal wave are obtained under the assumption that the pump wave is undepleted. For the parameters considered the longitudinal component is shown to be negligible.     

Photorefractive effects in long, narrow BSO crystals with applied electric field

In a photorefractive Bi₁₂SiO₂₀ crystal with high applied electric ac field of square-wave shape a fast two-wave coupling response (less than 1 s) and a slow hologram readout decay (minutes) was found for a wavelength of 633 nm. This can be explained by electron–hole transport with two trap levels. An intensity dependence of the slower complementary grating was found. Illuminating with the readout wave without applied electric field leads to a very slow grating decay (many hours). Received: 18 November 1998 / Revised version: 3 February 1999 / Published online: 7 April 1999     

Coherent radiation under conditions of the propagation of heavy charged particles through the dielectric in an external electric field

The process of electromagnetic radiation arising during the propagation of heavy charged particles through a dielectric layer situated in an external electric field is investigated. This radiation is due to the degradation of polarization medium induced by the field. The local maximum within the centimeter frequency range of the energy spectrum is analyzed under varying external parameters of the model. Conditions that might allow for the intensity of the radiation to be comparable to the transition radiation are found.     

Photovoltaic solitons in two-photon photorefractive materials under open-circuit conditions

We present the evolution equation of one-dimensional spatial soliton in two-photon photorefractive media under open-circuit conditions. In the steady state regime, our solutions show that the dark and bright photovoltaic spatial solitons can be supported in two-photon photorefractive media under open-circuit conditions.     

Impurity-related intraband absorption in coupled quantum dot-ring structure under lateral electric field

The effects of a lateral electric field on intraband absorption in GaAs/GaAlAs two-dimensional coupled quantum dot-ring structure with an on-center hydrogenic donor impurity are investigated. The confining potential of the system consists of two parabolas with various confinement energies. The calculations are made using the exact diagonalization technique. A selection rule for intraband transitions was found for x-polarized incident light. The absorption spectrum mainly exhibits a redshift with the increment of electric field strength. On the other hand, the absorption spectrum can exhibit either a blue- or redshift depending on the values of confinement energies of dot and ring. Additionally, electric field changes the energetic shift direction influenced by the variation of barrier thickness of the structure.     

Determination of temperature and concentration of molecular nitrogen,oxygen and methane with coherent anti-stokes raman scattering

Temperature and concentration measurements by Coherent Anti-Stokes Raman Scattering (CARS) of molecular nitrogen, oxygen and methane were carried out. A comparison of corrected thermocouple and CARS temperature measurements in a high-temperature furnace up to 2000 K is presented. The temperature dependent CARS spectra of N₂ and O₂ are evaluated by a simulation program. Agreement between CARS and thermocouple temperatures is obtained within 40 K for N₂ and 80 K for O₂. Good agreement is found between measurements and calculations of the decrease of CARS intensity with temperature. Various quick-fit methods for N₂-and O₂-temperature measurements from temperature sensitive spectral parameters were tested. Temperature dependent CARS spectra of thev ₁-fundamental of methane are recorded and the methane CARS intensity as function of temperature is measured.     

The effect of mid-infrared and far-infrared emission,generated at NH3 excitation by intense radiation of a TEA CO2 laser,on ammonia absorption

The effect of Mid-InfraRed (MIR) ( 12 m) and Far-InfraRed (FIR) ( 100 m) emission from excited ammonia on the absorption of intense radiation of a TEA CO₂ laser has been studied experimentally under collisional and collisionless excitation conditions with ammonia pressures from 0.5 to 0.03 Torr. The energy of MIR and FIR emission was studied as a function of NH₃ pressure and laser energy fluence. Particular emphasis was given to the kinetics of MIR and FIR emission generation at different NH₃ pressures and to the measurement of the time delay of re-emitted pulses relative to the exciting CO₂ laser pulse. It has been found that the re-emission in the MIR range is highly collisional in nature. The intensity of MIR emission drops sharply (asp ³) with decreasing NH₃ pressure and its delay time relative to the exciting laser pulse increases. At the same time, re-emission in the FIR range (in the case of resonant excitation of NH3 at the 9R (30) line of CO₂ laser) is observed during an exciting pulse up top < 0.03 Torr. When binding the rotational sub-levels of a molecule with transitions, FIR emission acts as rotational relaxation and thus leads to an increase in NH₃ IR absorption even at collisionless excitation.     

Generation of tunable infrared radiation in rubidium titanyl phosphate crystal for the optical measurement of number density, absorption cross-section of methane gas

Tunable near-infrared radiation has been generated in a rubidium titany1 phosphate (RTP) crystal by employing non-collinear difference-frequency mixing (DFM) technique. The input radiation sources are Nd:YAG laser radiation and its second harmonic pumped dye laser radiation. For the generation of 2.0 radiation, the maximum value of the conversion efficiency (quantum) obtained in the process is 49% from the dye (0.6945 μm) to the infrared (2.0 μm) radiation in the 7.9-mm-long crystal. The generated tunable mid-infrared radiation has been used to measure the number density, absorption cross-section and minimum detectable concentration of methane gas in its 2ν₃ band in a multi-pass cell at 30.075 Torr pressure. The number density and column density of the methane molecules are found to be 1.068×10¹⁸ cm⁻³ and 3.02×10²¹ cm⁻², respectively, whereas the minimum still-detectable concentration at 1.658 μm wavelength is estimated to be 4.523×10¹⁷/cm³.