Phase-conjugate Mirror Research Articles

Characterization of a Pico-Second Phase Conjugate Nd:YVO4 Laser System

We present a full characterization of a pico-second pulse generation from a Nd:YVO4 double-pass amplifier with a phase-conjugate mirror based on a photorefractive BaTiO3 crystal with an external loop geometry. With this system, 7.4 W diffraction-limited pico-second output was generated. A corresponding optical extraction efficiency of >20% was achieved.

Development of High Repetition LD-Pumped Solid-State Laser

In the Leading Project of MEXT from 2003, Japan, high average power LD-pumped YAG lasers are being developed with specifications of > 1 J, > 5 kHz, and 1-10-ns pulse. All fiber front end system consists of cw 40-mW Yb doped fiber laser (YbDFL) with a fiber Bragg grating cavity, a pulse shaper of LiNbO3, and three stages of YbDFL amplifiers, delivering 2-mW average power of 1-20 ns pulses in 5-kHz repetition rate. The design and test of 500-W class LD-pumped booster amplifier head is discussed. Some key elements of technology for high-peak and high-average power system are reviewed such as a ten-cm silica laser material, a repetitive work of stimulated Brillouin scattering phase conjugate mirror for 10-kW capability, a ceramic material for Faraday rotator for high-average power level, so on.

Improvement of Thomson Scattering Diagnostics Using Stimulated-Brillouin-Scattering-Based Phase Conjugate Mirrors

In order to improve the measurement performance of incoherent Thomson scattering diagnostics, a high performance phase conjugate mirror based on stimulated Brillouin scattering (SBS-PCM) is applied to a Thomson scattering system for the first time in the JT-60U tokamak. We have demonstrated that a SBS-PCM which uses heavyfluorocarbon liquid showed a high reflectivity of 95% at a high input-power of 145 W. Using the SBS-PCM, two newly developed methods were employed to increase the amount of scattered light. In the first method, we first developed a new optical design to provide a double-pass scattering scheme with the SBS-PCM. In this new optical design, a laser beam passing through the plasma is reflected by the SBS-PCM, and the reflected beam is returned via the same path by means of the phase conjugate effect, and is then passed through the plasma again, in order to increase the scattered light. A double-pass Thomson scattering scheme using the SBS-PCM was demonstrated in JT-60U ohmic plasma, resulting in an increase of the scattered light by a factor of 1.6, and the reduction of relative error by 2/3 for electron temperature measurement in contrast to single-pass scattering. A multi-pass Thomson scattering scheme is also proposed based on the results of double-pass scattering. It is estimated that multi-pass scattering allows the generation of several times the amount of scattered light, and the reduction of the relative error for electron temperature measurement by 37% in contrast to single-pass scattering. Regarding the second method, a high average-power of YAG laser system was developed by applying the SBS-PCM to a existent diagnostic laser. As a result, the average-power was increased by over 8 times in contrast to the average power of the original system, achieving up to 368 W (7.4 J × 50 Hz).

Control of Reflectivity by Beam Polarization State In Self-Pumped Phase Conjugation Mirror Using Photorefractive Polymer

The photorefractive(PR)properties of two kinds of the double-layered PR polymeric device are presented. As one of the application utilizing the merit of large gain for the multi-layered PR device, the function as a self-pumped phase conjugation mirror(SPPCM)is discussed. Theses devices show a promise for the optical logic device, since they strongly exhibit the incident beam polarization state dependence of the phase conjugation reflectivity.

Bifurcation analysis of a semiconductor laser subject to non-instantaneous phase-conjugate feedback

We consider how the behaviour of a semiconductor laser subject to phase-conjugate feedback depends on the interaction time of the phase-conjugating mirror. We employ continuation techniques to show how the bifurcation diagram in the plane of feedback strength versus pump current changes as the interaction time of the mirror is increased. This shows that for interaction times below 0.1 ns the assumption of instantaneous feedback is justified. On the other hand, we show that increasingly larger interaction times lead to considerable changes in the size and qualitative structure of the locking region. Our study provides a more global view of the suppression of complicated and chaotic dynamics.

Multi-watt diffraction-limited picosecond pulses from a diode-pumped Nd:YVO4amplifier with a photorefractive phase conjugate mirror

We demonstrate>4 W and 7.2 ps output of a double-pass Nd:YVO4 slab amplifier with a photorefractive ring phase conjugate mirror. A double-pass gain of 190 and optical extraction efficiency of >20% were obtained. The amplified signal beam exhibits a TEM00 profile with beam propagation parameters Mx2<1.4 and My2<1.1.

Phase conjugation of a quantum-degenerate atomic fermion beam.

We discuss the possibility of phase conjugation of an atomic Fermi field via nonlinear wave mixing in an ultracold gas. It is shown that for a beam of fermions incident on an atomic phase-conjugate mirror, a time-reversed backward propagating fermionic beam is generated similar to the case in nonlinear optics. By adopting an operational definition of the phase, we show that it is possible to infer the presence of the phase-conjugate field by the loss of the interference pattern in an atomic interferometer.

Phase conjugation of gap solitons: A numerical study

We study the effect of a nearby phase-conjugate mirror (PCM) on the gap soliton of a Kerr non-linear periodic structure. We show that phase conjugation of the gap soliton (in the sense of replication of the amplitude profile in the reverse direction) is possible under the condition of PCM reflectivity approaching unity. This is in contrast with the results for linear structures, where the wave profiles can be conjugated for arbitrary values of the PCM reflectivity. The sensitivity of the conjugation of the gap solitons to PCM reflectivity is ascribed to the fine balance of non-linearity with dispersion, necessary for their existence.

Optical phase conjugation in difference-frequency generation

We present a theoretical treatment of difference-frequency generation in conditions of phase mismatch for seed and generated fields that propagate at different angles to the pump. The analytical solution in the case of nondepleted plane-wave pump and experiments performed with seed fields strongly phase and amplitude modulated show that the pump-field wave fronts behave as efficient phase-conjugating mirrors.

Enhancement of spectral purity of injection-seeded titanium:sapphire laser by cavity locking and stimulated Brillouin scattering.

We report improvements to and better characterization of the spectral purity of a diode laser injection-seeded, cavity-locked titanium sapphire laser that serves as the source for a previously reported rubidium vapor spectrally filtered Thomson scattering apparatus at 780.24 nm. In a detailed set of measurements the spectral purity P of the laser, defined as the ratio ofthe narrowband component of the laser output to the total output, has been studied as a function of frequency mismatch between the seed laser frequency and the central frequency of the unseeded cavity. It is found that spectral purity exceeding 0.999 can be obtained for a seed-cavity mismatch as high as +/- 0.25 nm, corresponding to approximately 950 cavity longitudinal-mode spacings and as high as approximately 0.9999 for a cavity-seed mismatch in the range +/- 0.10 nm (380 mode spacings). It is also shown that the addition of an external-cavity stimulated Brillouin-scattering phase-conjugate mirror increases both the spectral purity, to a minimum of 0.99999, and the cavity-seed mismatch range, to +/- 0.25 nm, for which this maximum effective purity is obtained.

Fused-quartz glass with low optical quality as a high damage-resistant stimulated Brillouin-scattering phase-conjugation mirror

Fused-quartz glass is found to be an ideal medium for high-power stimulated Brillouin-scattering experiments, because it gives a high reflectivity of over 95% at an incident energy of 2.3 J, has pulse duration of 16 ns, and has excellent fidelity in phase conjugation. The low optical homogeneity of the fused-quartz material selected resulted in a low focusability at the focus, resulting in a reduction in laser-damage occurrence, even in high-energy operations. Despite this fact, its conjugation fidelity is good for cancellation as a phase-conjugated mirror. All solid-state lasers with high-beam qualities, based on phase-conjugated mirrors with fused-quartz glass are highly suitable for use as laser sources in many applications.

自己励起位相共役鏡の波面補償特性とその応用 : レーザーからディスプレイまで(表示記録用有機材料およびデバイス)

自己励起位相共役鏡の波面補償特性とその応用 : レーザーからディスプレイまで(表示記録用有機材料およびデバイス)

Stabilization of the photorefractive double phase-conjugate mirror inBaTiO3

Photorefractive simple and double phase-conjugate mirrors very often exhibit strong instabilities in their reflectivities. One of their possible origins can be the competition between phase conjugation and its generating process, photorefractive beam fanning. However, by suitably choosing the incident beam widths and directions, we suppressed this competition and replaced it by the enhancement of each process by the other. This technique allows to obtain a double phase-conjugate mirror in BaTiO{sub 3} that establishes itself in seconds for beam intensities on the order of the tenth of a milliwatt. The reflectivities reached are on the order of 30% and stable within 3% for hours.

Comparison of adaptive optics and phase-conjugate mirrors for correction of aberrations in double-pass amplifiers.

Correction of birefringence-induced effects (depolarization and bipolar focusing) were achieved in double-pass amplifiers by use of a Faraday rotator between the laser rod and the retroreflecting optic. A necessary condition was ray retrace. Retrace was limited by imperfect conjugate-beam fidelity and by nonreciprocal refractive indices. We compared various retroreflectors: stimulated-Brillouin-scatter phase-conjugate mirrors (PCMs), PCMs with rod-to-PCM relay imaging (IPCM), IPCMs with astigmatism-correcting adaptive optics, and all-adaptive-optic imaging variable-radius mirrors. Results with flash-lamp-pumped, Nd:Cr:GSGG double-pass amplifiers showed the superiority of adaptive optics over nonlinear optic retroreflectors in terms of maximum average power, improved beam quality, and broader oscillator pulse duration/bandwidth operating range. Hybrid PCM-adaptive optics retroreflectors yielded intermediate power/beam-quality results.

YAG Laser Perfomance Improved by Stimulated Brillouin Scattering Phase Conjugation Mirror in Thomson Scattering Diagnostics at JT-60

An improvement of the output energy of a multistage YAG laser system by using a stimulated Brillouin scattering (SBS) phase conjugation mirror (PCM) was achieved. The phase conjugation of the optically nonlinear SBS process in a liquid material effectively compensated thermal degradation at an average/peak power amplifier, resulting in an average power increase from 1.5 J at 30 Hz repetition rate to 2.6 J at 50 Hz drive. The beam quality was also recovered without wave front deformation and depolarization resulting in a transfer-limited divergence with a good flat-top pattern in a near field.

유도 브릴루앙 산란 위상공액 거울을 이용한 Nd:YAG 레이저 발진기의 출력특성

유도 브릴루앙 산란 위상공액 거울을 이용한 Nd:YAG 레이저 발진기의 출력특성

Spectrally Filtered Raman/Thomson Scattering Using a Rubidium Vapor Filter

A new spectrally e ltered light scattering apparatus is presented based on a diodelaser injected seeded titanium: sapphire laser and rubidium vapor e lter at 780.24 nm. It is shown that the realizable line center attenuation of quasi elastically scattered light, limited by a residual broad spectral linewidth, unseeded, component to the laser output, isashigh as 1 :67£10 5 using the laser system alone. Preliminary measurementsindicatethat incorporation of a set of dispersing prisms and a stimulated Brillouin scattering phase conjugate mirror external to the laser provides an additional approximate factor of 10 extinction. The utility of the system for measurement of electron density and temperature by Thomson scattering is demonstrated in a 3950-Pa (30-torr) argon dc discharge. At 100-mA current, an electron density of 3 :7£1013 cmi3 is measured on the discharge centerline with a 2 ae value of statistical uncertainty equal to 8 :0£10 11 cm i3 . The corresponding electron temperature is 0 :63§ 0:025 eV.

Laser-diode phase-conjugate interferometer for distance measurement

A laser-diode (LD) phase-conjugate interferometer with two self-pumped (cat) phase-conjugate mirrors instead of two ordinary mirrors is constructed for distance measurement over extended ranges. The measurement is based on frequency-modulated continuous-wave techniques. A wide-tunable LD with an external cavity is used as a light source in a phase-conjugate wavefront-matched interferometer. The interferometer is insensitive to spatially nonuniform phase distortion, but can only detect the spatially uniform phase change introduced by the displacement of one cat mirror. The linear regression of the measured beat frequency as a function of the distance has been ascertained.

Ring self-pumped phase-conjugate mirror with a photorefractive Ba 0.77Ca 0.23TiO 3 crystal as an active medium

The generation of oscillations in a ring self-pumped phase-conjugate mirror (RSPPCM) with a photorefractive Ba 0.77Ca 0.23TiO 3 crystal (BCT) as an active medium is shown. The interplay of a reflection and a transmission grating is observed, whereas the threshold of the RSPPCM can be reduced by the reflection grating. The internal phase-conjugate reflectivity inside the ring of the RSPPCM tends asymptotically to 100% for an intensity of the pump wave higher than 40 mW/mm 2.

Dynamic effect of phase conjugation on wave localization

We investigate what would happen to the time dependence of a pulse reflected by a disordered single-mode waveguide if it is closed at one end, not by an ordinary mirror, but by a phase-conjugating mirror. We find that the waveguide acts like a virtual cavity with resonance frequency equal to the working frequency ${\ensuremath{\omega}}_{0}$ of the phase-conjugating mirror. The decay in time of the average power spectrum of the reflected pulse is delayed for frequencies near ${\ensuremath{\omega}}_{0}.$ In the presence of localization the resonance width is ${\ensuremath{\tau}}_{s}^{\ensuremath{-}1}\mathrm{exp}(\ensuremath{-}L/l),$ with L the length of the waveguide, l the mean free path, and ${\ensuremath{\tau}}_{s}$ the scattering time. Inside this frequency range the decay of the average power spectrum is delayed up to times $t\ensuremath{\simeq}{\ensuremath{\tau}}_{s}\mathrm{exp}(L/l).$