Transient degenerate four wave mixing in saturable absorbers

The transient behaviour of degenerate four wave mixing (DFWM) in a three-level saturable absorber is analysed. We discuss two cases which are relevant to present day experiments. We obtain the transient reflectivity in the cases where the pump beams consist of (a) a single pulse and (b) a train of pulses.     

Highly efficient degenerate four-wave mixing with multipass geometries in a polymer laser dye saturable amplifier

We demonstrate the use of highly efficient degenerate four-wave mixing for phase conjugation with multipass geometries in a polymer laser dye saturable amplifier. Phase-conjugate energy reflectivity of as much as 20,000% with a four-pass geometry in the longitudinally pumped polymer dye was obtained at 564 nm.     

Steady-state pulses in degenerate swept-gain amplifiers

In the high-gain region of a Q(J)-symmetric degenerate, swept-gain amplifier, it is shown that superradiant steady-state pulses propagating at the speed of light can arise as solutions of the equations of motion. Equilibrium positions for the population inversions are calculated, assuming that the time taken to attain a steady state is very much shorter than the naturalv lifetimes of the levels, and that the cooperative emission lifetimes may be very short.     

近简并四波混频相位共轭介质中的光强分布

从求解耦合波方程出发，详细研究了非线性光学介质中由近简并四波混频所产生的相位共轭过程。以上述波方程的解为基础，给出作为混频结果的反射传播相位共轭波沿介质轴向的光强分布，得到比以往文献中所报道的更为精确的结果，从而为选择工作物质的最佳尺寸提供了理论依据。     

Experimental characterization of semiconductor optical amplifiers used as frequency converters by means of four-wave mixing

In this article we report extended measurements of four-wave mixing in bulk-semiconductor amplifiers using continuous wave sources. We demonstrate that four-wave mixing in semiconductor amplifiers permits realizing in the practice frequency conversion in the spectral range of utility for optical telecommunications. Efficiency larger than 1 have been demonstrated up to 1 THz with a low level of background noise. In addition, this technique has allowed us to investigate the carrier dynamics down to an equivalent time resolution of the order of few tens of femtoseconds.     

Transient analysis of degenerate four-wave mixing in saturable absorbers: application to Cr:GSGG at 1.06 μm

We introduce a model of degenerate four-wave mixing in saturable absorbers in the transient regime when the interacting pulses have a duration much shorter than the lifetime of the excited-state level. Our model takes into account of the depletion and the mutual interaction of the pump waves. We study the influence of excited-state absorption on phase conjugate reflectivity. This theory agrees with experimental investigations made in Cr⁴⁺:GSGG with nanosecond pulses at λ₀ = 1.06 μm. A reflectivity of 0.6% is achieved and imaging capabilities are demonstrated.     

Transient degenerate four-wave mixing in molecular systems

The dependence of the degenerate four-wave mixing (DFWM) signal on laser intensity, molecular transition moment and molecular concentration were examined experimentally by taking the iodine molecule (l₂) as a testing example. The experimental results will be interpreted by a non-steady-state DFWM theory, an extension of the non-degenerate two-level system previously proposed. The distinctive physical feature of this mechanism is that the present observation is the result of non-stationary evolution of the excited-state population, in contrast to the conventional theory based on the steady-state treatment. In this study, we have also taken into account the magnetic sub-levels of molecular rovibronic quantum states. The non-steady-state model we developed in this paper is applicable to fast pump and slow relaxation conditions, thus being more suitable for gas-phase systems than the condensed-phase where fast relaxations usually take place.     

Optical chaos in multiple degenerate four-wave mixing

Spatial evolution has been studied of an ensemble of equal-frequency light waves involved in several four-wave mixing processes under linear photoabsorption. It is shown that this system may exhibit spatial chaos caused by competition of optical mixing processes with strong energy exchange between the waves. For pulsed radiation, the temporal envelopes of interacting waves undergo modulations which may also be of chaotic character. Also discussed are possible variants of identifying chaos in systems of interacting light waves experimentally and the role of accompanying photoprocesses (photoabsorption, self-action of radiation).     

Theory of degenerate four-wave mixing in three-level atoms

We derive a theoretical model for phase conjugation in three level atoms. The atoms are assumed to be at rest and the intensities I₁ and I₂ of the pump beams can take arbitrary large values. We calculate the lineshape for a thin optical medium in the case of plane waves and of gaussian beams. In the case of a thick optical medium, we show that the gain saturates if I₁ ≠ I₂.     

Stability of localized structures in degenerate wave mixing

We give experimental proof of the stability of (supercritical) spatial phase solitons in degenerate wave mixing. Received: 16 June 1999 / Published online: 25 August 1999     

The effects of collisional quenching on degenerate four-wave mixing

We report a theoretical and experimental investigation of the effects of collisional quenching on resonant degenerate four-wave mixing (DFWM). Using single-mode laser radiation, peak signal intensity measurements were performed on an isolated line in the A – X transition of NO. By using appropriate mixtures of N₂ and CO₂ as buffer gases, we varied the collisional quenching rate over several orders of magnitude while maintaining a fixed total collisional dephasing rate. The mixtures had approximately 100 Torr total pressure and were at room temperature. For I/I _sat approximately equal to 0.02, DFWM intensities were found to be less affected by variations in quench rate than were laser-induced fluorescence (LIF) intensities (I and I _sat are the pump laser and one-photon saturation intensities, respectively). Moreover, for I/I _sat roughly equal to 0.5, DFWM intensities were observed to be nearly independent of quench rate. The results are compared to two theoretical predictions, with good agreement observed. Both theories indicate that the minimum sensitivity of DFWM to quenching occurs near I/I _sat1.     

Alternative method of implementation of frequency encoded N bit comparator exploiting four wave mixing in semiconductor optical amplifiers

A frequency encoded all optical N bit comparator is proposed. The implementation is ultrafast one and the frequency encoding makes it intensity loss dependent problem free. The use of polarization insensitive four wave mixing makes the design polarization independent and the hardware simple. The frequency conversion by the RSOA makes the design faster compared to other SOA based design. The required gates, i.e. X-OR and AND gates for the implementation of the comparator in frequency encoded format are also discussed.     

Quantum statistics of degenerate four wave mixing

A microscopic model of degenerate four wave mixing including the quantisation of the atomic medium is analysed. In the limits of large detuning, low saturation and zero loss, ideal squeezing in the output field is possible. The effect of nonoptimal conditions is analysed.     

Effects of a modulation of the pump-polarization in a degenerate pump/probe experiment

The effects of the pump-polarization in a degenerate pump/probe experiment are analyzed. It is shown that modulating the pump polarization from linear to circular induces a modulation in the probe absorption change that allows to separate various contributions that are mixed in the signal. An experimental demonstration is carried out in a laser dye (Coumarin 500). Received: 21 July 1998 / Revised: 28 October 1998 / Accepted: 20 November 1998     

Atomic mixing in ion probe microanalysis

The atomic mixing due to a knock-on cascade has much influence on the depth resolution of ion probe microanalysis. The preliminary experimental results support the assumption that the depth resolution due to this effect is determined by the competition of sputtering rate and creation rate of atomic displacement.     

Quantum statistics of the degenerate four-wave mixing process

A quantum mechanical treatment is given of the degenerate four-wave mixing process. The approximate Heisenberg equation of motion for creation and annihilation operators is solved taking into account attenuation and noise. The solution and the statistics of the modes are discussed both below and above the threshold condition.