Self-pumped Phase-conjugate Mirror Research Articles

Self-Q-switching of a loop laser cavity with a self-pumped four-wave phase-conjugate mirror in an active laser medium

Self-Q-switching of a loop laser cavity with a self-pumped four-wave phase-conjugate mirror in an active laser medium with the use of a Faraday isolator or a passive Q-switch is studied theoretically. It is found that, in contrast to passive Q-switching of an ordinary cavity, a passive Q-switch in a loop phase-conjugate cavity serves as an auxiliary unit that increases the self-Q-switching efficiency by gain gratings in the active laser medium, since it decreases the difference in the intensities of waves that write a phase-conjugate mirror in the active medium, which is similar to the use of a Faraday isolator. However, the passive Q-switch operates alternating the highly efficient writing of a phase-conjugate mirror in the closed state with the highly efficient generation of a giant laser pulse in the open state, which stabilizes the period of repetitive laser pulses.

Discovery of a self-pumped, phase-conjugate mirror with high speed, high image quality, and large accepted incidence area

A study for the incidence geometry to extend the accepted incidence position is presented and demonstrated. High-speed and high-quality self-pumped phase conjugate mirrors (SPPCM) can be formed with a counter-direction incidence with respect to the master light for the Cat-SPPCM. In addition to a counter-directional Kitty-SPPCM, when the incidence position is changed, a Kitty-SPPCM with high-pass filtering and a different SPPCM similar to the Bridge-SPPCM can be found. The discovery of these three kinds of optical phase conjugators extends the accepted incidence position range and angle, helpful for applying the SPPCM in various new applications.

A method for controlling the phase locking of a multichannel laser system

The conditions leading to control over phase-locked oscillation in a set of three loop lasers containing self-pumped phase-conjugate gain-grating mirrors by using a LiF: F2− passive Q-switch are studied both experimentally and theoretically. Cases of spatially uniform lamp pumping and high-efficiency spatially nonuniform transverse diode pumping are considered.

Loop laser cavities with self-pumped phase-conjugate mirrors in low-gain active media for phase-locked multichannel laser systems

It is proved that lasers with different loop cavities with self-pumped phase-conjugate mirrors in low-gain active media can operate under injection of external laser radiation and can be used for the development of diode-pumped phase-locked multichannel neodymium laser systems operating both on the fundamental laser transition with the wavelength λ = 1.06 μm and on the transition with λ = 1.34 μm. The phase-conjugate oscillation thresholds in the case of injection of an external signal are determined for a multiloop cavity configuration and an increased number of active elements in the cavity. It is shown that phase-conjugate oscillation can occur even if the single-pass gain of the active element is as low as only ∼2. Under high-power side diode pumping of a multiloop Nd:YAG laser, single-mode output radiation was achieved at λ = 1.064 μm with a pulse energy up to 0.75 J, a pulse repetition rate up to 25 Hz, an average power up to 18.3 W, and an efficiency up to 20%. In a multiloop Nd:YAG laser with three active elements in the cavity, single-mode radiation at λ = 1.34 μm was obtained with a pulse energy up to 0.96 J, a pulse repetition rate up to 10 Hz, and an average power up to 8.5 W.

Control of phase locking in a set of lasers with self-pumped phase-conjugate gain-grating mirrors using a passive Q-switch

We studied the possibility of controlling phase-locked lasing of a set of lasers with self-pumped phase-conjugate gain-grating mirrors by using a passive Q-switch and selecting the gain of one of the lasers. The ranges of stable operation are calculated by mathematical simulation and well agree with the experimental results. Single-mode radiation in the form of trains of phase-locked laser pulses are experimentally obtained for the first time in a three-channel diffraction-coupled gain-grating Nd : YAG laser system with a LiF :F −2 passive Q-switch. The space-time pattern of the trains of 1.064-μm nanosecond pulses is the same in the channels with and without Q-switch and their interference pattern contrast reaches 0.81.

Study of diffraction-coupled lasing in a set of lasers with self-pumped phase-conjugate mirrors on gain gratings in the case of short-range coupling

Compact schemes of a multichannel holographic laser system with short-range coupling and increased efficiency of single-mode lasing are developed for low-gain laser media operating not only at the fundamental laser transition but also at other laser transitions of the Nd:YAG crystal. The numerical simulation shows that the maximum possible number of laser channels can be increased by equalising their parameters. The possibility of phase locking of two loop Nd:YAG lasers without a nonreciprocal element with the free-running single-mode lasing efficiency up to 0.64% and the contrast of the interference pattern of the output beams exceeding 0.5 is shown experimentally.

Dynamics of photorefractive self-pumped phase-conjugate mirrors with a linear resonator

The phase-conjugation dynamics in a self-pumped phase-conjugate mirror (SP PCM) based on a BaTiO3 photorefractive crystal (PRC) with a linear resonator is simulated numerically. It is shown that a phased array of dynamic holograms is formed in such a SP PCM under optimal conditions, and the interference of the waves scattered by this array provides the very high stationary phase-conjugation efficiency (the nonlinear reflection coefficient and overlap integral exceeding 80% and 95%, respectively). It is found that the development of instabilities is caused both by the violation of phase relations in this array and the formation of additional dynamic holograms in the PRC in the geometry typical of a SP PCM with a semi-linear resonator and by the self-bending effect typical of PRCs.

Optical information security system using an interference-based computer-generated hologram and <inline-formula><math altimg="none" display="inline" overflow="scroll"><mrow><msub><mi>BaTiO</mi><mn>3</mn></msub></mrow></math></inline-formula>

This paper proposes a novel simple image encryption and decryption technique based on the principle of interference and a binary-phase computer-generated hologram (BPCGH). To obtain a stable interference pattern, a technique involving a photorefractive material is also proposed. The proposed scheme is composed of digital encryption and optoelectronic decryption. For the encryption process, a BPCGH that reconstructs the original image perfectly is designed, using a simulated annealing algorithm, and the resulting hologram is regarded as the image to be encrypted digitally. In addition, a reference image with key information is created using a random two-phase generator. The hologram is then encrypted using the reference image and the interference rule. For the decryption process, the interference intensity is obtained by interfering the reference image and the encrypted image, binarized with software, and then transformed into phase information. Finally, the original image is recovered by an inverse Fourier transformation of the binary-phase information. During this process, since the intensity information generated by the interference of the two images is very sensitive to external vibrations, a stable interference pattern is achieved using a self-pumped phase-conjugate mirror made of the photorefractive material BaTiO 3 .

Preliminary training of a self-pumped loop phase-conjugate mirror based on a photorefractive crystal

It is shown by the example of a loop self-pumped phase-conjugate (SPPC) mirror based on a photorefractive crystal (PRC) BaTiO3 that formation of a phase-conjugate (PC) wave in a SPPC mirror can be considerably accelerated by using a preliminary training of the mirror. For this purpose, it is necessary to direct preliminary an auxiliary (training) optical field on the SPPC mirror, which contains some information on the properties of the input signal whose wave front will be conjugated later. This procedure provides the writing of static refractive-index gratings in the PRC already at the training stage. The presence of these gratings ensures a much more rapid (by 6–20 times) production of volume refractive-index gratings required for the efficient conjugation of the signal radiation. Several variants of static and dynamic SPPC mirror training procedures are simulated and their efficiencies are compared.

Highly efficient phase-conjugation of a 1 µm pico-second Laguerre-Gaussian beam

We have demonstrated highly efficient Laguerre Gaussian beam generation by using a ring self-pumped phase conjugate mirror in the pico-second regime for the first time. The phase conjugate reflectivity was typically ~55%. We have also investigated the conservation of optical angular momentum.

Interferometric fidelity of self-pumped phase conjugation in BaTiO3 and a four-wave mixing set-up with Bi12SiO20 using nanosecond pulses

The fidelity of a self-pumped phase conjugating mirror (SPPCM) in the so-called cat configuration is studied with an interferometric method for a cobalt-doped barium titanate crystal (BaTiO3:Co) under pulse illumination (8 ns, 532 nm). With this SPPCM a phase conjugating four-wave mixing set-up using the sillenite-type crystal Bi12SiO20 (BSO) was realized. It is shown that the fidelity of both phase conjugating processes under pulse illumination nearly reaches the fidelity of continuous-wave experiments.

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)

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.

A Novel Phase Conjugate Broad-Stripe Diode Laser with an External Ring Geometry

We present a highly bright output radiated from a single-stripe high power laser diode, known as a broad-stripe laser diode (BS-LD) with ring-type self-pumped phase conjugate mirror. Within a minute after the laser turning on, the lasing frequency was locked at the central wavelength of 808.9 nm within 0.1 nm. The BS-LD then generated a single-lobed far-field.

Demultiplexing and phase-locking via a self-pumped phase-conjugate mirror

We demonstrate a new type of time-integrative photorefractive device using self-pumped phase conjugation. This device can be used for most of the applications related to time-integrative devices, such as demultiplexors and phase-sensitive detectors. A new device for angular multiplexing-to-frequency multiplexing conversion is proposed. By combining this new device with frequency demultiplexing, we show a new architecture for retrieving holograms from different holographic storages and for performing various arithmetic operations on the retrieved information.

Photorefractive Materials and Their Applications. High-Power Nd:YAG laser Using Ring Self-Pumped Phase Conjugate Mirror.

A LD-pumped sigzag slab Nd:YAG oscillator-amplifier system using a photorefractive ring self-pumped phase conjugate mirror is developed. The photorefractive phase conjugator is optimized in the point view of high-energy pulse capacity, fidelity of phase conjugation and stability. The laser system generates the IR laser pulses of 600 mJ and the second harmonic pulses of 250 mJ at the repetition rate of 100 Hz. Both the IR and the second harmonic have 1.1 times diffraction limited beam quality.

Spatial subharmonics generation during recording of self-pumped phase-conjugate mirrors

Abstract The self-pumped phase-conjugate mirrors (SPPCM) recorded by a single beam incident in photorefractive Bi 12 TiO 20 crystals without external mirror under alternating electric field are presented. Simultaneously with the phase-conjugated wave we observe significant concentration of the scattered light on the direction of the subharmonics generation. This combined formation of the fundamental grating and its spatial subharmonics allows SPPCM formation in a much wider band of spatial frequency.

Increase in phase-conjugate reflectivity of a holographic Nd:YAG oscillator due to resonant refractive-index grating

We have studied both experimentally and numerically the role of resonant refractive-index gratings (RIGs) in a self-pumped phase-conjugate mirror based on an Nd:YAG amplifier with nonreciprocal feedback loop. In experiment the generation of the phase-conjugating laser was delayed with respect to the recording of a holographic nonlinear mirror by an external beam. An increase in the phase-conjugate reflectivity at a delay time of about 3 μs was measured. The numerical calculation confirmed the additional contribution that the resonant RIG formed in a pumped Nd:YAG crystal because of excitation of a higher-lying level of Nd 3+ ions make to the efficiency of phase conjugation.

Combined formation of a self-pumped phase-conjugate mirror and spatial subharmonics in photorefractive sillenites

We found that the formation of self-pumped phase-conjugate mirrors (SPPCM) in photorefractive Bi12TiO20 crystals under external alternating electric field is accompanied by strong enhancement of spatial subharmonics. This combined formation of the fundamental grating and its spatial subharmonics results in an expansion of the spatial-frequency band allowed for SPPCM recording.