Direct two-photon creation of a biexciton

The nonlinear absorption coefficient for the two-photon creation of biexciton in CuCl is calculated in the approximation of one intermediate, optically active excitonic state. The two-band model with realistic band structure at the band extrema is considered. The exciton-biexciton dipole transition momentum matrix element is expressed by the functional of the exciton and biexciton envelopes. In the numerical calculations the envelope of the Hylleraas-Ore type, modified by Brinkman et al., is used. Our calculated value of the absorption coefficient is about two orders of magnitude smaller than that estimated previously by Hanamura, and agrees better with the experimental value reported by Gale and Mysyrowicz.     

Parametric amplification of a coherent light wave in photorefractive BaTiO(3) by a single pump beam

We demonstrate a new method of light amplification based on forward four-wave mixing in photorefractive BaTiO(3). A single pump beam of combined (ordinary and extraordinary) polarization can be used for an efficient cw amplification of a signal wave with slightly shifted temporal frequency. A signal wave with an initial power of less than 1 nW is amplified ~100 times in a 3.2-mm-thick sample.     

Generation of femtosecond pulses by two-photon pumping supercontinuum-seeded collinear traveling wave amplification in a dye solution

Visible femtosecond (fs) laser pulses have been obtained in a dye solution with a very simple traveling wave collinear configuration. A femtosecond Ti:sapphire laser (790 nm) pumps the dye solution by two-photon absorption and simultaneously generates supercontinuum, which seeds a light-amplification mechanism. Cross-correlation frequency-resolved optical gating measurements reveal a chirped structure in the dye pulse. The shortest pulse duration achieved is 170 fs and the overall energy efficiency of the process is typically 25%. Received: 22 March 2001 / Revised version: 4 July 2001 / Published online: 19 September 2001     

Optical nonlinear self-oscillations near the two-photon resonance of biexciton

Nonlinear self-oscillations in a coherent interacting polariton-biexciton system in optically excited semiconductors are theoretically investigated. A systematic linear stability analysis of steady-state bistable solutions is presented and a self-consistent procedure for a numerical integration of the nonlinear dynamic equations is proposed as well.     

Absorption spectroscopy using a coherent transition radiation millimeter wave light source

The characteristics and applicability of the absorption spectroscopy system using the coherent transition radiation light source have been investigated. The configurations of the system are relatively simple. The operational conditions of an electron linear accelerator have been evaluated. The stability of the light intensity has been within ±2–3% in a wavenumber range of 4–13 cm⁻¹. The light intensity has been found to be more than six orders of magnitude higher than that for the lowest limit for detection.     

Bistability in coherent two-photon processes

Using the coupled Maxwell-Bloch equations for coherent two photon processes, we show the existence of bistable behavior of systems undergoing coherent two photon resonant processes such as two photon absorption and Raman process. The system is taken to be contained in a ring cavity. The dependence of the bistable behavior on detuning parameter and the Stark shifts is also discussed.     

Lineshapes in coherent two-photon excitation

We compare lineshapes obtained in laser-induced fluorescence and resonantly enhanced multi-photon ionisation, resulting from coherent pulsed excitation of a two-photon transition in xenon atoms. We find that excitation profiles probed by ionisation show power broadening as expected. Here ionisation occurs simultaneously with the coherent excitation. The profiles observed by fluorescence show almost no broadening, because of coherent population return, since the fluorescence occurs predominantly after the excitation pulse is over. Thus the observed lineshape depends characteristically upon the nature of the probing process.     

Theory of coherent two-photon absorption

An exact solution for the propagation of two ultrashort pulses through a two-photon near resonant absorbing medium is obtained under the condition that the initial number of photons/s cm² in the two pulses are the same. High-power pulses develop sharp peaks as they propagate through the medium.     

Photon statistics in saturated m-photon amplification and attenuation of coherent light

The change of photon statistics of a nearly coherent single-mode light beam travelling through a saturable m-photon-amplifying or absorbing medium (m = 1, 2, …) is theoretically investigated. With the help of an approximation scheme valid for $\text{n}$ ? 1, Δn² ? $\text{n}$² ($\text{n}$ mean value and Δn² variance of the photon number) an analytical expression is derived for the quantity Δn²/$\text{n}$. The results holds for arbitrary values of the initial population inversion and of the degree of saturation. It turns out that for both amplification and attenuation processes after sufficiently strong interaction Δn²/$\text{n}$ tends to an asymptotic value.     

Study on the biexciton in CdS by low intensity non linear coherent mixing

We report the unambiguous observation of biexciton in CdS by non linear spectroscopy using four wave degenerate frequency mixing. The two-photon autoionizing character of this level is shown to be responsible for the dissymetric line shape of the third order non linear susceptibility resonance. Polarization experiments display the role of intermediate quasi-resonance on A1 and B1 excitons and huge exciton-biexciton strengths.     

Quantum coherent control of two-photon transitions by square phase-modulation

A femtosecond laser pulse can be tailored to control the two-photon transitions using the ultra-fast pulse-shaping technique. This paper theoretically and experimentally demonstrates that two-photon transitions in molecular system with broad absorption line can be effectively controlled by square phase-modulation in frequency domain, and the influence of all parameters characterizing the square phase-modulation on two-photon transitions is systemically investigated and discussed. The obtained results have potential application in nonlinear spectroscopy and molecular physics.     

Chaotic motion of atom in the coherent field of a standing light wave

A new effect of chaotic motion of the center of mass of a cold atom in the coherent field of a standing light wave in a high-finesse Fabry-Pérot cavity is theoretically predicted and numerically implemented in the absence of any random fluctuations due to spontaneous emission. Numerical experiments demonstrate that the Hamiltonian chaos arises near resonance in the range of parameters characteristic of the strong coupling regime that was implemented in recent experiments. The effect is of interest in studying the quantum-classical correspondence and quantum chaos in atomic optics.     

X-ray amplification by laser controlled coherent bremsstrahlung

A coherent x-ray generation scheme is proposed which involves characteristics of free electron lasers and atomic high harmonic generation schemes. A thin solid layer or any other periodic atomic structure with limited dimensions is exposed to a short, superintense laser pulse. The electrons are extracted from the layer due to the extreme force and penetrate periodically through the ionic structure. Consequently, thousands of harmonics of the laser radiation field are shown to coherently amplify along the interaction length. The small signal gain of the generated x-ray radiation exceeds that arising from the multiphoton Compton process in plasmas and is competitive with that in the leading x-ray free electron lasers.     

Holography,coherent light amplification and optical phase conjugation with photorefractive materials

This paper presents a review of photorefractive effects in electro-optic materials and their applications. Materials properties giving rise to increased photo-sensitivities are discussed and compared with experimental data for a series of newer materials. The formation of volume holograms in these crystals, and accompanying optical effects such as beam coupling and phase conjugation, are discussed. Theoretical results derived from charge transport parameters are compared with our original data obtained in “dynamic holography” experiments with Bi₁₂GeO₂₀, Bi₁₂SiO ₂₀ and KNbO₃:Fe²⁺. The optimum parameters for applications such as volume hologram storage, coherent light amplification, optical phase conjugation etc. have been determined, and possible applications are discussed.     

Femtosecond pulse amplification by coherent addition in a passive optical cavity

By simultaneously controlling repetition and carrier frequencies, one can achieve the phase coherent superposition of a collection of successive pulses from a mode-locked laser. An optical cavity can be used for coherent delay and constructive interference of sequential pulses until a cavity dump is enabled to switch out the amplified pulse. This approach will lead to an effective amplification process through decimation of the original pulse rate while the overall coherence from the oscillator is preserved. Detailed calculations show the limiting effects of intracavity dispersion and indicate that enhancement of sub-100-fs pulses to microjoule energies is experimentally feasible.     

Discrete coherent amplification of oscillations by nonresonant forcing

A new mechanism of generation of oscillations in a linear forced oscillatory system is found. Natural oscillations may be generated at a "sharp" pulse (rapid variation) of the natural frequency. In this process oscillations are generated by nonresonant forcing, e.g., by the action of a constant, nonperiodic or periodic force (with driving frequency much less than the natural one). Repetitive pulses of the natural frequency result in emergence of oscillations that interfere and may give a powerful resultant output. These phenomena relate to a basis of the theory of open linear oscillatory systems.     

Interferometric registration of electromagnetic field phase jumps in coherent amplification of light pulses

Phase evolution in the process of coherent amplification in Nd: YAG and ruby at 100 K is investigated. Streak camera scans of interference fringes are used. Phase jumps corresponding to field envelope sign reversal and to intensity oscillations are observed.