150-times phase conjugation by degenerate four-wave mixing in a continuous-wave Nd:YVO4 amplifier

The high phase-conjugate reflectivity of 150, by four-wave mixing in a diode-pumped Nd:YVO₄, has been demonstrated. The phase-conjugate mirror was capable of correcting the phase aberration of a probe beam. The experimental diffraction efficiency of the transmission gratings was 60. Received: 8 April 2002 / Revised version: 10 June 2002 / Published online: 25 September 2002 RID="*" ID="*"Corresponding author. Fax: +81/43-290-3490, E-mail: omatsu@image.tp.chiba-u.ac.jp     

Picosecond phase-conjugation by degenerate four-wave mixing in sodium vapour

Phase-conjugated waves (PCW), via degenerate four-wave mixing (DFWM) with picosecond laser pulses having a FWHM of 80 ps have been obtained in sodium vapour on both sides of theD ₂(3² S _1/23² P _3/2) transition at 589 nm. The maximum reflectivity of the PCW signals was 60%. The reflectivity of the PCW has been measured as a function of the temperature, the detuning and the pump and probe intensities. Because of the very strong nonlinear behaviour of theD ₂ transition the appearance of the PCW is accompanied by strong self-focusing and defocusing of the beams, which give a rather complicated line-shape of the detuning curve of the PCW. By varying the delay between the beams, the lifetime of the transient volume grating has been, measured to be 7.4 ns. The results are in qualitative agreement with the theoretical model of Abrams and Lind.     

Comparison between c-cut and a-cut Nd:YVO4 lasers passively Q-switched with a Cr4+:YAG saturable absorber

Comparison between c-cut and a-cut Nd:YVO₄ microchip lasers passively Q-switched with a Cr⁴⁺:YAG saturable absorber is experimentally made. The lower emission cross section of the c-cut Nd:YVO₄ crystal can enhance the passive Q-switching effect to produce a peak power 10 times higher than that obtained with the a-cut crystal. The experimental result further reveals that a c-cut Nd:YVO₄ crystal is a very convenient material for short-pulse (sub-nanosecond) and high-peak-power (>10 kW) lasers. Received:10December2001/Revisedversion:22January2002 / Published online: 14 March 2002     

Photorefractive four-wave mixing with partially coherent light beams

Received: 11 April 1997/Revised version: 22 May 1997     

Study of non-linear optical phase conjugation in Ca by resonant degenerate four-wave mixing via bound excited states

. The dependence of the reflectivity on the vapour density, the buffer gas pressure and the pump beams intensity was investigated. The influence of the strong linear absorption was taken into account in a theoretical model that led to a satisfactory interpretation of the experimental results. A maximum reflectivity of 46% was measured under optimized conditions. The effect was also studied through the high-lying bound states . The maximum measured reflectivity was as high as for the first excited state. The effect of the oscillator strength on the reflectivity was demonstrated experimentally and interpreted with the help of a simple theoretical model. Received: 11 June 1996     

Phase conjugation in a continuous-wave diode-pumped Nd:YVO4 laser

We demonstrate phase conjugation and dynamic holography by degenerate four-wave mixing in a continuous-wave diode-pumped Nd:YVO₄ laser for the first time. A phase-conjugate reflectivity of 1.4% is obtained with a 12 W diode power. The experimental results and the optimizing parameters, such as the cavity mirror reflectivities, are compared with results from a steady-state theoretical analysis. Received: 6 April 1999 / Published online: 24 June 1999     

Doppler-free spectroscopy and wave-front conjugation by four-wave mixing of nonmonochromatic waves

A new technique to determine the natural and collision width of Doppler-broadened two-photon transitions is shown. The method consists of using the pump with the spectral width considerably exceeding the Doppler one of the transition. Feasibility of effective wave front conjugation is shown for the case of radiation with a large spectral width.     

A selection equilibrium theory for “stimulated photorefractive backscattering and four-wave mixing” self-pumped phase conjugation

Received: 7 March 1997/Revised version: 21 July 1997     

Molecular enhanced four-wave parametric generation in sodium atom

A number of resonances have been observed in the excitation spectrum of the uv resonance lines of sodium. The mechanism proposed includes absorption by molecular states, energy transfer to excited atomic levels and four-wave parametric generation enhanced by radiative decay of the excited states.     

Instability and satellite pulse of passively Q-switching Nd:LuVO4 laser with Cr:YAG saturable absorber

This work presents experimental results concerning a passively Q-switching Nd:LuVO₄ laser with a Cr⁴⁺:YAG saturable absorber operated in a three-element cavity. When the pump power exceeded 5.47 W, the system transfers stable pulse train into spatial-temporal instability. Furthermore, the chaotic pulse train accompanied the generation of a satellite pulse. The experimental results reveal that the mechanisms of instability and generation of the satellite pulse are governed by the multitransverse mode competition.     

Photorefractive mutually pumped phase conjugation with partially coherent beams

We investigate the mutually pumped phase-conjugation process in photorefractive media with partially coherent pump beams. We consider the effects of transmission, reflection, and 2k-reflection gratings as well as the depletion of both pump beams. The theoretical results can be employed to qualitatively explain the experimental observations.     

Nd:YAG激光在单晶硅中的四波混频相位共轭

以单晶硅作非线性介质,用调Q脉冲Nd:YAG激光作四渡混频,获得了相位共轭反射光波.从光激发电子-空穴对浓度及其所产生的相位光栅出发,理论计算了相位共轭镜的反射率.实验获得的共轭镜反射率为125%,并与实验中显示了其对相位干扰的补偿特性.     

Collinear nondegenerate four-wave mixing by a three-level system

Four-wave mixing in the vicinity of a sodium doublet is reported. The three-level system allows collinear phase-matching. The FWM is resonantly enhanced by a high gain on the blue side of the D₁ transition.Present address: LROL, Physics Department, Laval University, Quebec, Canada, G1K 7P4To whom correspondence should be addressed     

Review of four-wave mixing and phase conjugation in plasmas

Four-wave mixing (FWM) in plasmas and its applications to phase conjugation (PC) and plasma diagnostics have been extensively studied. Plasmas have received considerable attention, since they become more efficient four-wave mixing and phase conjugation mediums at longer wavelengths (far-infrared ~10 μm to radiowave ~10 m) for which there are few other nonlinear mediums. In addition, FWM shows great potential as a plasma diagnostic. Recent advances in the experimental and theoretical study of FWM and PC in plasmas are reviewed     

Compact low threshold Cr:YAG passively Q-switched intracavity optical parametric oscillator

We report a compact KTP-based intracavity optical parametric oscillator (IOPO) driven by a diode-end-pumped passively Q-switched Nd:YVO₄/Cr:YAG laser. For the first time, we take the thermal lens effect of the Cr:YAG into consideration and discuss its impact on the signal output. Diode pump threshold as low as 0.52 W has been achieved, which is the lowest result reported to date. At the incident diode pump power of 4 W, we obtained the maximum signal average and peak power of 358 mW and 12.5 kW, respectively, corresponding to a diode-to-signal conversion efficiency of 9%. Moreover, cavity-dumping characteristic and pulse transforming process from 1064 to 1573 nm are qualitatively analyzed.     

Pulse compression in AO Q-switched diode-pumped Nd:GdVO4 laser with Cr4+:YAG saturable absorber

By simultaneously using both an acoustic-optic (AO) modulator and a Cr⁴⁺:YAG saturable absorber in the cavity, for the first time, a diode-pumped doubly Q-switched Nd:GdVO₄ laser has been realized. The pulse duration is obviously compressed in contrast to the actively acoustic-optic Q-switched laser. By considering the Gaussian transversal distribution of the intracavity photon density and the longitudinal distribution of the photon density along the cavity axis as well as the influence of turnoff time of the acoustic-optic (AO) Q-switch, we provide the coupled rate equations for a diode-pumped doubly Q-switched Nd:GdVO₄ laser with both an acoustic-optic (AO) modulator and a Cr⁴⁺:YAG saturable absorber. These coupled rate equations are solved numerically, and the dependence of pulse width, pulse energy and peak power on the incident pump power at different pulse repetition rates is obtained. The numerical solutions of equations agree well with the experimental results.This revised version was published online in August 2005 with a corrected cover date.     

Coupled cavity modelocking of a Nd:YAG laser using second-harmonic generation

The modelocking of a Nd:YAG laser using second-harmonic generation in an external cavity as the only pulse shortening process is reported. The output of a long pulse Nd:YAG laser was simultaneously modelocked and Q-switched. The average pulse duration was 30–50 ps and the peak power was in the range 60–160 kW.     

Phase conjugation in potassium vapour using subnanosecond laser pulses

Phase conjugated waves (PCW) were generated for the first time by degenerate four-wave mixing with subnanosecond laser pulses in potassium vapour near the D ₁ transition at 7699 Å. The light source was a long cavity grazing incidence dye laser. The pulses had a duration of 700–800 ps and a linewidth of 0.2 Å. The experiments were performed in a temperature range of 400–550° C. A maximum reflectivity of 57% has been observed together with temporal pulse shortening. PCW reflectivity has been measured as a function of the temperature, and the backward pump intensity.     

In-line Nd:YAG resonator using self-pumped phase conjugation in Cr(4+):YAG

We report the operation of an in-line Nd:YAG resonator using self-pumped phase conjugation in Cr(4+): YAG at lambda=1.064microm in the nanosecond regime. The output beam has a high-quality diffraction-limited TEM(00) mode and a pulse shape of ~15ns , showing the self- Q -switching ability of the resonator. A maximum extraction of 18mJ and a maximum reflectivity of 2.0 are measured. A transient model provides insight into the energy characteristics and the dynamics of such an in-line resonator.