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We demonstrate an end-pumped, c-cut Nd:YVO4 laser that emitted first-order Laguerre-Gaussian (LG01) beam by adjusting the position of focused pump beam relative to laser crystal. The pumping light reached the laser crystal has circular and solid intensity profile. The laser is compact and stable, and the obtained LG01 beam power reaches 202 mW with ~25% slope efficiency.

We demonstrate a linearly-polarized, ytterbium-doped fiber laser that uses an uncoated, undoped ceramic YAG plate as the output coupler, and the corresponding polarization extinction ratio of laser beam increases with incident pump power and then saturates at larger pump power. For comparison, the output coupler of the fiber laser is replaced by 10% reflectivity plane mirror, while the feature of the polarization of laser output is kept unchanged. The results show that the origin of the pump-dependent and self-started polarization is associated with the intensity-dependent nonlinear birefringence in the gain fiber.

We presented a proof-of-concept investigation upon an end-pumped and vortex Nd:YAG laser. In this laser, for the first time, the conical refraction (CR) ring of a biaxial KGd(WO4)2 crystal was used for annular pumping. Owing to nearly 100% conversion efficiency in forming the CR ring, the Nd:YAG laser was highly efficient and emitted LG01-mode vortex light with 177.5 mW beam power and 65% slope efficiency. This study showed the CR ring pumping would favor the production of a compact, simple and efficient vortex laser. It is expected that, in future, the CR ring pumping technique would also facilitate the high-power vortex solid-state laser where a long gain medium is required.

We report on a radially polarized and passively Q-switched Nd:YAG/Cr4+:YAG laser. The bulk Nd:YAG crystal is bonded with two undoped YAG crystal end caps to weaken the thermal lens e?ect and thus, enhance the extraction of stored energy in the bulk gain material. In the absence of active water cooling, the average laser power reaches 383 mW with 33% slope e±ciency, and the laser pulse achieves 1.457-W peak power, 18.9-ns duration, and 13.9-kHz repetition rate with 97.6% polarization purity.

We reported our proof-of-concept investigation in developing an arrayed and passively Q-switched Nd:YVO4 laser. In the investigation, we used a Dammann grating to diffract the pumping light from a 808 nm laser diode into 2×2 pump beam array, and then used this pump array to pump a monolithic Nd:YVO4 laser crystal standing with a Cr4+:YAG saturable absorber inside a simple plano–plano resonator. As a result, 2×2 arrayed and nanosecond laser pulses were emitted. The laser-diode-pumped monolithic solid-state laser incorporated with a Dammann grating is promising for application in high-peak-power and multipoint pulse ignition of an automobile engine.

The photorefractive holographic recording is a dynamic grating formulation process, where the grating is induced by the interference modulation of two beams, and the energies of the beams are exchanged with each other owing to their interaction in the induced grating. The grating modulation envelope is a comprehensive analysis for holographic dynamic recording and non-destructive readout, but analytic solutions can only be obtained by simultaneously solving the materials equations and the coupled wave equations. In this paper, based on Kukhtarev's model and Moharam's field function exact steady-state analytic expressions for dynamic grating envelopes are deduced for any constant values of light modulation depth and light excitation efficiency. Thus their approximations for straight formulation instead of parametric formulation are then obtained. These steady-state analytic solutions to envelopes describe the dynamic holographic recording and readout more clearly and exactly.

The photorefractive holographic recording and two-beam coupling are both dynamic grating formulation process. The interference light intensity of the two coherent beams induces a phase grating though photo-induced refractive index variation and the phase grating changing the intensities of the two beams through beam-coupling take place at the same time. By solving simultaneously the band transport equations and wave-coupled equations, and using the light intensity modulation as the main variable, the analytic solution is obtained, which is valid for any light intensity modulation and constant light excitation efficiency. Here all the mechanics of drift, diffusion and photovoltaic effect are considered. The result shows that the modulation of the dynamic grating varies more slowly compared with that of the linear modulation approximation.

The transient interaction between a refraction index grating and light beams during simultaneous writing and thermal fixing of a photorefractive hologram is investigated. With a diffusion- and photovoltaic-dominated carrier transport mechanism and carrier thermal activation (temperature dependent) considered in Fe:LiNbO3 crystal, from the standpoint of field–material coupling, the theoretical thermal fixing time and the space-charge field buildup, spatial distribution, and temperature dependence are given numerically by combining the band transport model with mobile ions with the coupled-wave equation. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 23: 372–376, 1999.

A scheme using a CO 2 laser beam to thermally fix selective layers or lumps of photorefractive holograms to integrate and miniaturize an optical three-dimensional system into a single block of LiNbO 3 crystal is suggested. Theoretical and experimental investigations on laser local thermal lixing are given, and a stage of the modified gamma network is demonstrated experimentally.

An arrayed-output Nd:YVO4 laser is demonstrated in which the collimated pumping light is split into 2×2 array by a Dammann grating and thus forms four independent pumping areas in one single laser crystal.

An laser-diode (LD) end-pumped Nd-doped Yttrium Vanadate (Nd:YVO4) laser was demonstrated to emit the first order Laguerre-Gaussian (LG01) mode. This LG01-mode laser is compact and efficient.

The anharmonic potential felt by a single-species ions confined in a rf quadrupole trap which results from a non-ideal trap configuration and the charge distribution of the ion cloud is studied. The rf resonance-absorption spectra are explained by a Duffing oscillator and a representation of the line-shape parameter η is derived. Forη > 0.77, the electric signals will exhibit hysteresis. The relation with the anharmonic potential is discussed.

By introducing a circular Dammann grating (CDG) into the pump unit, we demonstrated an end-pumped Nd:YAG laser that emitted a vortex and first-order LG mode with high laser efficiency and high power. In our scheme, the CDG was used to reshape the pumping light into an annular profile, and the adaptation of it was realized easily by inserting it into the pump unit of a conventional end-pumped solid-state laser; the laser cavity was simple, compact, and consisted of only a laser crystal and an output coupler. The beam power of this laser reached 1.86 W at an absorbed pump power of 6.38 W with a slope efficiency of 34.5%.

Radially polarized light attracts much attention because of its applications in high-precise metal cutting, optical tweezers and other fields. Many schemes have been developed to force the radial-polarization excitation in laser resonator by employing various intracavity polarization selectors, such as birefringent crystal and/or conical Brewster window [1]. These methods, however, are applicable only in a limited range of laser output power [1], and encounter big challenges in improving the laser efficiency, beam's cylindrical symmetry and polarization purity simultaneously. In recent years the photonic crystal grating (PCG), one kind of three-dimensional sub-wavelength gratings, appeared as an effective polarization-dependent element which can provide the specified reflectivity/transmission to the radial polarization and thus can play as the output coupler of laser resonator for desired polarization. Such grating mirror shows unique superiority when combining with compact and end-pumped microchip laser in providing high polarization purity and excellent modal symmetry as well as high laser efficiency embodied in the radial-polarization emission [2]. However, the thermal lens effect in the end-pumped microchip gain medium remained as an obstacle for further power scaling, and so far the output power from such laser is kept in the hundreds milliwatts level. An efficient, high-power and compact solid state laser that emits radially polarized light with high polarization purity would be extremely desirable.

A simulated annealing algorithm is adopted to give an automatic pump configuration in laser-diode backward-pumped-distributed fiber Raman amplifiers. The demonstration of the optimization process of wavelengths and powers in an optical-fiber Raman amplifier using four laser-diode pumps is presented. The resulting gain ripple is less than 2.6 dB in respect to the 30 dB average gain in the amplification bandwidth of more than 50 nm (64 signal channels). The algorithm can be practically applied to the desired signal channel number and gain profile.

In distributed optical fiber Raman amplifiers, instantaneous pump power depletion is related to the patterns of the input wavelength-division-multiplexing signals, especially for high bit rate application. This results in additional optical noise and interchannel crosstalk. We analyzed the phenomenon and presented simulation results. The cases for different bit rates and channel numbers were compared.

A simulated annealing algorithm is adopted to design multiple-pump Raman fiber amplifiers. A demonstration of the optical fiber Raman amplifier using five laser diode pumps with different wavelengths and powers is presented. The automatic configuration of the pump gives an amplification bandwidth of more than 50 nm (64 signal channels), with a fluctuation of less than 1.8 dB. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 30: 434–436, 2001.

We report, for the first time to our knowledge, a radially polarized and passively Q-switched Yb-doped fiber laser. By using a Cr(4+):YAG crystal as a saturable absorber and a photonic crystal grating as a polarization mirror, a radially polarized pulse is produced, which has 202 W of peak power, 75 ns duration, and ~92% polarization purity at a 56.6 kHz repetition rate. The Q-switched pulse with radial polarization from the fiber laser would facilitate numerous applications.

High-peak power and nanosecond Q-switched lasers pulse with axisymmetrical polarization could find significant in industrial areas for marking, trimming, and machining, and also in particle manipulation [1] and optical tweezers etc. There is no doubt that the construction of such a new type of laser source, which emits axisymmetrically polarized pulse with high-peak power and short duration, would mention the combination of the passive Q switching technique and polarization control technique. In this paper a LD end-pumped Nd:YAG ceramic microchip laser passively Q-switched by Cr4+:YAG absorber is demonstrated to generate axisymmetrically polarized pulse. The reason to employ the end-pumped microchip laser lies in the fact that such cavity configuration is beneficial carrier both for producing energetic Q-switched pulse and also the axisymmetrical polarization [2].

Cylindrical vector beams were produced from laser diode end-pumped Nd:YAG ceramic microchip laser by use of two types of subwavelength multilayer gratings as the axisymmetric-polarization output couplers respectively. The grating mirrors are composed of high- and low-refractive- index (Nb(2)O(5)/SiO(2)) layers alternately while each layer is shaped into triangle and concentric corrugations. For radially polarized laser output, the beam power reached 610mW with a polarization extinction ratio (PER) of 61:1 and a slope efficiency of 68.2%; for azimuthally polarized laser output, the beam power reached 626mW with a PER of 58:1 and a slope efficiency of 47.6%. In both cases, the laser beams had near-diffraction limited quality. Small differences of beam power, PER and slope efficiency between radially and azimuthally polarized laser outputs were not critical, and could be minimized by further optimized adjustment to laser cavity and the reflectances of respective grating mirrors. The results manifested, by use of the photonic crystal gratings mirrors and end-pumped microchip laser configuration, CVBs can be generated efficiently with high modal symmetry and polarization purity.

The radially polarized mode is achieved from an active Yb fiber by utilizing of an intracavity converging axicon, where the axicon acts as a TM(01) mode selector based on not only its Brewster convex surface but also the distance between its vertex and plane output coupler. The polarization state of the annular laser beam is checked by using a home-made eight-hole aperture. Furthermore, an uncoated plane glass plate is inserted into the cavity, and the reflected beam points to the existence of an annular lasing mode inside the gain fiber. The issues for developing high-power radially polarized fiber lasers also are considered.

This presentation will describe the recent improvements in Yb-fiber laser by applying a converging axicon. The measured results reveal this annular beam has a radial polarization with a polarization extinction ratio in the range from 2.3 to 4.4.

An ytterbium-doped fiber laser was demonstrated to emit azimuthally polarized light with high laser power and efficiency, in which a birefringent yttrium vanadate (YVO(4)) crystal was used as the intracavity polarization discriminator. The laser power reached 3.94 W with a slope efficiency of ∼71%. Our study proved that an efficient, high-power vector fiber laser would be realistic under the utilization of a simple and low-cost birefringent crystal as polarization discriminator.

We report a simple Nd:YAG laser that emits radially polarized beam with helical wavefront. The laser cavity consists of a piece of laser crystal and a plane output coupler, and there is no additional polarization component inside it. The pump light is converted into annular profile through de-focal coupling into a multi-mode fiber. For the continuous-wave (CW) operation, the laser emits radially polarized vortex beam, and it is observed that the helical wavefront of the laser beam is switched from right handedness to left handedness when the output coupler is tilted slightly. For the Q-switched operation under the insertion of a Cr4+:YAG saturable absorber inside the cavity, we obtain radially polarized outputs with left-handedness helical wavefront. By tilting the laser crystal slightly, the laser output switches to azimuthal polarization at pump power larger than 4.5 W and left-handedness helical wavefront of laser beam is preserved.

Self-pulsing instabilities in Yb-doped fibre laser are investigated with pump-bypassed cavity configuration. The correlation between both the temporal traces of signal and pump reveals the accurate mechanism of self-pulsing instabilities.

The finite recovery time Ts of the bleached absorber is presented as one of the possible mechanisms accounting for the increase-maximum-decrease in pulse energy E with the pumping rate Wp in cw-pumped passively Q-switched solid-state lasers, by analytically evaluating the sign of the derivative partial differentialE/ partial differentialWP. The results show that, in the low pump regime (T>Ts, T is the interpulse period), the initial population density ni remains constant, the final population density nf decreases with Wp, and this results in a monotonic increase of E with Wp. In the high pump regime (T

Self-pulsing instability in the ytterbium-doped fiber (YDF) laser is investigated with the pump-bypassed cavity configuration. The residual pump light acts as a probe of the intracavity dynamics, and the temporal behavior of the light shows correlations with the self-mode locking instability in the original cavity and the sustained self-pulsing instability in the modified cavity of the YDF laser. The results suggest that the interactions among stimulated emission, pump absorption and/or reabsorption could account for self-pulsing instability in the YDF laser. The pump-bypassed laser cavity configuration can be used to investigate the instabilities of various kinds of fiber lasers.

Good beam quality, stable longitudinal multi-mode oscillation caused by spatial hole burning was studied in laser-diode pumped Cr, Yb: YAG self-Q-switched microchip laser.

The PARSEC laser system is designed for the VLT Laser Guide Star Facility to deliver a high power cw laser beam at 589nm, in order to create an artificial guide star in the mesospheric Sodium layer. The laser consists of a resonant, dye based power amplifier which is injection seeded with 589nm, single frequency radiation from a master oscillator. We report on the performance of the system both during the European Acceptance tests, and that which has been achieved in the laboratory. The maximum power we have obtained amounts to 20W cw laser light in a single mode and a single frequency at 589nm. With a beam quality of M2 of 1.05-1.15 and a long term stability without manual intervention, the laser suits all the demands for operation at the VLT.

One of the critical design drivers for the PARSEC laser was that by the time it is integrated into the VLT Laser Guide Star Facility in 2003 it should be able to run remotely without any hands-on tuning for a period of at least one week. In this contribution we describe some of the methods we have employed to achieve this and take a brief look at the proposed operating procedure.

For the successful operation of laser referenced adaptive optic systems very powerful lasers for the creation of sodium guide stars are necessary. Here we introduce the design of PARSEC, the cw sodium-line laser for the VLT, and present out first laboratory results on the performance of the system. So far we have achieved a stable output power of 12.8W in a single spatial mode and a single frequency.

Distributed fiber Raman amplifiers will be deployed in long-haul optical transmission system with certain advantages. Also there is a trend to deploy dense dispersion management. In this paper, we discuss the combination of the two technologies to design a 4000 km long transmission system with 40 Gbit/s RZ pulses format. Simulation results are presented and optimal dispersion compensation scheme is evaluated.

The transient temperature evolution in the gain medium of a continuous wave (CW) end-pumped passively Q-switched microchip (PQSM) laser is analyzed. By approximating the time-dependent population inversion density as a sawtooth function of time and treating the time-dependent pump absorption of a CW end-pumped PQSM laser as the superposition of an infinite series of short pumping pulses, the analytical expressions of transient temperature evolution and distribution in the gain medium for four- and three-level laser systems, respectively, are given. These analytical solutions are applied to evaluate the transient temperature evolution and distribution in the gain medium of CW end-pumped PQSM Nd:YAG and Yb:YAG lasers.

Photorefractive doubly doped Fe:Mn:LiNbO3 crystal is the most promising material to record nonvolatile photorefractive holograms by photochromic effect, and is very useful for the reconfigurable integration of miniaturized optical 3-D systems within a crystal substrate. In this paper by recording few nonvolatile and spatially- local holographic gratings in a single block of photochromic Fe:Mn:LiNbO3 photorefractive crystal, we presented a new technique to implement miniaturized Mach-Zehnder interferometer sensor integrated in bulk sample(s). The interferometer was self-adaptive and used to detect or monitor the temperature changes as one arm of the interferometer is exposed in a thermal field. The design and analysis on the performance are shown, and the experimental results are given. This sensor has the advantage of simple construction over the conventional sensor and optical fiber sensor.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A CO2 laser beam has been suggested to heat the Fe:LiNbO3 to thermally fix a recorded hologram. This optical/thermal method permits to spatially locally and selectively fix, erase or update photorefractive holograms in-situ and in real time. The thermal field distribution in LiNbO3 induced by the heating of a CO2 laser beam is in fact nonuniform, which has an effect on the fixing efficiency for the recorded hologram. In this paper, we developed the relation between the fixed space charge field amplitude Esc and the fixing temperature Tf. Then to evaluate the performance of the recorded and fixed local but nonuniform photorefractive holograms, two parameters of the localization coefficient (Psi) and the average space charge field amplitude Escave are defined, respectively. The relations among local hologram amplitude and locality and the nonuniform temperature field are discussed. An optimum temperature field caused by the CO2 laser heating is achieved. The developed method is suitable for the other boundary conditions and laser beam profiles.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The photorefractive grating formulation is a dynamic process which means that the interference light intensity of the two coherent beams inducing a phase grating through photo- induced refractive index variation and the phase grating changing the intensities of the two beam through beam- coupling take place at the same time. The analytic solution for such a grating formulation can be only obtained by simultaneously solving the material equations and the coupled wave equations. In this paper, using the Moharam's space-charge field function and the coupled wave equations, we first obtained the exact and approximate analytic solutions to the photorefractive grating with any light modulation depth and any constant light excitation efficiency. Here three step calculation idea has been used. These solutions help to understand the two-beam coupling effect and the interacted grating formulation process in physics more straightforward and in quantity more exactly.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A technique to record local non-volatile photorefractive holograms is developed by using the spatially selective UV sensitization in a photochromic Fe:Mn:LiNbO3 crystal. Correspondingly, the integrated modules of WDM Multiplexer/Demultiplexer, Add/Drop, Crossbar, and Cross-Connect are designed, and the proof-of-principle experiments are given.

This paper summarized our developments on the integration of miniaturized optical 3D systems using crystal substrates, which include a birefringence-customized stacking technique with the building blocks of double refraction and a photorefractive integration technique with the photorefractive local holograms thermally fixed by CO2 laser heating. The principles are introduced and the corresponding configurations are given, and the examples of various integrated digital optical computing systems such as logic processor, morphological image processor, and interconnection networks are shown.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We present, for the first time to our knowledge, a gray-level image recording method in photorefractive volume memory, in which the image to be recorded is illuminated periodically by a pulse while the reference beam interacts the medium continuously until the steady state is reached. By adjusting the duty cycle of the exposure of the image in recording, high fidelity can be maintained in image reconstruction for pixels of different gray-scale intensities. Furthermore, due to multiple beam coupling the weak input image can be greatly enhanced without the loss of fidelity.

Surface plasmon (SP) mediated near band-edge emission in Ag/ZnO nanorods has been systematically studied by using a temperature-dependent photoluminescence spectra technique. It was found that the mediation mainly concerns SP couplings with two emissions, one from neutral donor-bound exciton D0X recombination and another from the radiative transition of free electron to neutral acceptor (e, A0). The first coupling process is demonstrated to prevail in the temperature range from?300 to 150?K, while the second is dominant below 150?K. The competition mechanism and the role of exciton and carrier delocalizations in the coupling processes have been explored in the unique Ag/ZnO nanostructures.

We demonstrate an ytterbium-doped fiber laser that emits high-power radially polarized light efficiently. In this study, a photonic crystal grating (PCG) was used as a polarization-selective output coupler, and the power of the radially polarized laser reached 2.42 W with a slope efficiency of 45.9% and a polarization purity of 96%. The results reveal that the inclusion of the PCG mirror into the fiber laser are particularly promising for generating high-power radially polarized light efficiently in view of its many important applications.

For the first time to our knowledge, a radially polarized beam is generated in an Yb-doped multimode double-clad fiber laser by using an intracavity dual conical prism. Up to 6.2 mW of output power is obtained from a 2 m long gain fiber with 7.4% slope efficiency. This research opens a new window to obtaining a radially polarized beam directly from an active fiber.