Cadmium Selenide Polymer Microfiber Saturable Absorber for Q-Switched Fiber Laser Applications

We demonstrate the generation of a Q-switching pulse train in an erbium-doped fiber laser （EDFL） cavity using a newly developed cadmium selenide （CdSe） based saturable absorber （SA）. The SA is obtained by embedding CdSe nanomaterials into a polymethyl methacrylate （PMMA） microfiber. It is incorporated into an EDFL cavity to generate a Q-switched laser operating at 1533.6nm. The repetition rates of the produced pulse train are tunable within 37–64kHz as the pump power is varied from 34mW to 74mW. The corresponding pulse width reduces from 7.96μs to 4.84μs, and the maximum pulse energy of 1.16nJ is obtained at the pump power of 74mW.

A novel hybrid surface micromachined segmented mirror for large aperture laser applications

A novel hybrid surface micromachined segmented mirror array is described. This device is capable of scaling to large apertures for correcting time-varying aberrations in laser applications. Each mirror is composed of bottom electrode, support part, and mirror plate, in which a T-shaped beam structure is used to support the mirror plate. It can provide mirror with vertical movement and rotation around two horizontal axes. The test results show that the maximum deflection along the vertical direction of the mirror plate is 2 μm, while the rotation angles around x and y axes are±2.3° and ±1.45°, respectively.

Survey and technological analysis of laser and its defense applications

The laser technology has made remarkable progress over the past couple of decades.It is being widely employed in diverse domains,such as holography,space sciences,spectroscopy,medical sciences,micro and power electronics,industrial engineering,and most distinctively,as directed energy military weapons.Owing to their active transmissions,laser systems are similar to microwave radars to some extent;however,unlike conventional radars,the laser operates at very high frequencies thus making it a potent enabler of narrow-beam and high energy aerial deployments,both in offensive and defensive roles.In modern avionics systems,laser target indicators and beam riders are the most common devices that are used to direct the Laser Guided Weapons(LGW)accurately to the ground targets.Additionally,compact size and outstanding angular resolution of laser-based systems motivate their use for drones and unmanned aerial applications.Moreover,the narrow-beam divergence of laser emissions offers a low probability of intercept,making it a suitable contender for secure transmissions and safety-critical operations.Furthermore,the developments in space sciences and laser technology have given synergistic potential outcomes to use laser systems in space operations.This paper comprehensively reviews laser applications and projects for strategic defense actions on the ground or in space.Additionally,a detailed analysis has been done on recent advancements of the laser technology for target indicators and range-finders.It also reviews the advancements in the field of laser communications for surveillance,its earlier state of the art,and ongoing scientific research and advancements in the domain of high energy directed laser weapons that have revolutionized the evolving military battlefield.Besides offering a comprehensive taxonomy,the paper also critically analyzes some of the recent contributions in the associated domains.

Guest Editorial Special Issue on Mid-Infrared Lasers and Applications

Mid-infrared （mid-IR） lasers, generally defined as having an operation wavelength in the spectral region of 2μm to 20μm, have attracted great scientific and technological interests owing to their widespread applications. This wavelength range not only contains some strong vibration transitions of many important molecules, thus, exhibiting enormous potential in medical, spectroscopy.

The Application of Laser Plasma in Ophthalmology

In this paper the production and development of laser plasma is introduced, and the contrlbutlon of laser biomedicine and laser plasma technology to ophthalmology is analyzed. In the end, the latest three progresses (laser photocoagulation, photorefractive keratotomy and laser lridectomy of laser plasma applications in ophthalmology are preserited.

The Application of Laser Processing on Clutch Manufacture

The first multi-function laser processing system in the domestic for clutch manufacture,with abilities of cutting, jointing and heat treatment,was reported in this paper.One external optical path,double laser heads,adjust device by manual operation,automatically track were employed in this system Also the other parts of vehicles can be fabricated by this system,as well as clutches.The special processing to manufacture the clutches of heavy vehicles,which was developed by the project of this laser processing system,achieved the international standards and satisfied the economic development and nation defense in the do- mestic.

Influence of adhesive layer properties on laser-generated ultrasonic waves in thin bonded plates

This paper studies quantitatively the generation of Lamb waves in thin bonded plates subjected to laser illumination, after considering the viscoelasticity of the adhesive layer. The displacements of such plates have been calculated in the frequency domain by using the finite element method, and the time domain response has been reconstructed by applying an inverse fast Fourier transform. Numerical results are presented showing the normal surface displacement for several configurations： a single aluminum plate, a three-layer bonded plate, and a two-layer plate. The characteristics of the laser-generated Lamb waves for each particular case have been investigated. In addition, the sensitivity of the transient responses to variations of material properties （elastic modulus, viscoelastic modulus, and thickness） of the adhesive layer has been studied in detail.

WIDE-BAND LASER CLADDING: WEAR AND CORROSION RESISTANCE OF A Ni-BASED ALLOY

A novel wide-band laser cladding system, with high rate of cladding, has been developed in the present work. The system mainly consisted of a 5kW CO2 laser, an automatic powder feeder and a wide-band scanning rotative polygon mirror which can produce a linear or rectangular focused laser beam. Using this system, a Ni-Cr-Si-B alloy powder was cladded on the surface of type 321 austenitic stainless steel in order to improve its wear and corrosion resistance. The pitting corrosion, high temperature oxidation and wear tests were conducted in order to evaluate the properties of the laser cladded layer. The results demonstrated that the cladded layer can significantly improve the adhesive wear and pitting corrosion resistance of the substrate. Moreover, the cladded layer exhibited good oxidation resistance, which is almost the same as that of GMR-235D Ni-based superalloy.

EFFECT OF LASER CLADDING ON HYDROGEN EMBRITTLEMENT RESISTANCE OF AUSTENITIC STAINLESS STEEL

A plasma spraying plus laser remelting technique has been performed. onaustenite stainless steel (22Cr-13Ni-5Mn ) with a newly developed hydrogen resistantcoating material. The results show that the surface cladding layer can effectively reducethe hydrogen content increasing of the stainless steel under the atmosphere of high pres-sure (30MPa), high temperature (300℃) and high purity (99. 995%) hydrogen andgreatly improve the hydrogen embrittlement resistance of the stain1ess steel. Throughanalysis of microstructure, a mechanism of hydrogen embrittlement resistance is presentedthat at room temperature, the surface oxidation films, both existing on the surface ofcoated and uncoated specimens, inhibit the adsorption and diffusion of hydrogen molecu-lae. However, at high temperature, it is the surface cladding layer with relatively low sol-ubility and Permeability for hydrogen that significantly reduces the amount of hydrogenentering into the interior of the material and improves its hydrogen embrittfement resis-tance.

13.5 mJ polarized 2.09μm fiber-bulk holmium laser and its application to a mid-infrared ZnGeP2 optical parametric oscillator

A high pulse repetition frequency（PRF）, high energy Ho：YAG laser directly pumped by a Tm-doped fiber laser and its application to a mid-infrared ZnGeP_2（ZGP） optical parametric oscillator（OPO） is demonstrated.The maximum polarized 2.09 μm laser pulse energy is 13.46 mJ at a PRF of 1 k Hz. The corresponding peak power reaches 504 kW. In a double-resonant ZGP-OPO, a maximum mid-infrared laser pulse energy of 1.25 m J,corresponding to a peak power of 79 kW, is accomplished at a PRF of 3 kHz. The nonlinear conversion efficiency reaches 41.7%. The nonlinear slope efficiency reaches 53.3%.

Rectification of 3D Data Obtained from Moving Range Sensor by Using Extended Projective Multiple View Geometry

To measure the 3D shape of large objects, scanning by a moving range sensor is one of the most efficient methods. However, if we use moving range sensors, the obtained data have some distortions due to the movement of the sensor during the scanning process. In this paper, we propose a method for recovering correct 3D range data from a moving range sensor by using the multiple view geometry under projective projections in space-time. We assume that range sensor radiates laser beams in a raster scan order, and they are observed from two cameras. We first show that we can deal with range data as 2D images, and show that the extended multiple view geometry can be used for representing the relationship between the 2D image of range data and the 2D image of cameras. We next show that the extended multiple view geometry can be used for rectifying 3D data obtained by the moving range sensor. The method is implemented and tested in synthetic images and range data. The stability of the recovered 3D shape is also evaluated.

The application of laser reflective tomography in near-field measurements of ultrasonic transducers

With Laser Reflective Tomography（LRT）,the near fields of ultrasonic transducers were measured and analyzed.The principle of LRT measurement of ultrasonic field distribution was introduced and an experimental system was set up.Acoustic pressure of a multiple element piston transducer was measured by using of a laser vibrometer.Its distribution in amplitude and phase was obtained.The acoustic pressure in the same region was measured with a needle hydrophone to validate the LRT method.Furthermore,through reconstruction of acoustic fields,it indicated that LRT method is suitable for predicting the distribution on transducers＇surface and conditions of active elements.

MOCVD growth of AlGaInP/GaInP quantum well laser diode with asymmetric cladding structure for high power applications

In order to improve the characteristics of the general broad-waveguide 808-nm semiconductor laser diode （LD）, we design a new type quantum well LD with an asymmetric cladding structure. The structure is grown by metal organic chemical vapor deposition （MOCVD）. For the devices with 100-ttm-wide stripe and 1000-/zm-long cavity under continuous-wave （CW） operation condition, the typical threshold current is 190 mA, the slope efficiency is 1.31 W/A, the wall-plug efficiency reaches 63%, and the maximum output power reaches higher than 7 W. And the internal absorption value decreases to 1.5 cm^-1.

Design and calibration of an elliptical crystal spectrometer for the diagnosis of proton-induced x-ray emission(PIXE)

Laser-driven proton-induced x-ray emission(laser-PIXE) is a nuclear analysis method based on the compact laser ion accelerator. Due to the transient process of ion acceleration, the laser-PIXE signals are usually spurted within nanoseconds and accompanied by strong electromagnetic pulses(EMP), so traditional multi-channel detectors are no longer applicable.In this work, we designed a reflective elliptical crystal spectrometer for the diagnosis of laser-PIXE. The device can detect the energy range of 1 keV–11 ke V with a high resolution. A calibration experiment was completed on the electrostatic accelerator of Peking University using samples of Al, Ti, Cu, and ceramic artifacts. The detection efficiency of the elliptical crystal spectrometer was obtained in the order of 10-9.

A novel dual-wavelength fiber Bragg grating and its application in fiber ring laser

A novel method for fabricating dual-wavelength fiber Bragg gratings (FBGs) by using one phase mask is developed. The method is based on a double-exposure technique. Our technique lends itself to writing gratings with controllable reflectivity and separation of two Bragg wavelengths. A grating with two equal transmission peaks of 20.25 dB is obtained by this method and the separation of the two Bragg wavelengths is about 0.8 nm. With the grating, we demonstrate a dual-wavelength erbium-doped fiber ring laser whose interval of the two peaks is 0.8 nm. The laser’s peak powers can get 3.1 mW above and have a good stability.

The application of sample-and-hold circuits in the laser frequency-shifting

A new method of frequency-shifting for a diode laser is realized. Using a sample-and-hold circuit, the error signal can be held by the circuit during frequency shifting. It can avoid the restraint of locking or even lock-losing caused by the servo circuit when we input a step-up voltage into piezoelectric transition （PZT） to achieve laser frequency-shifting.

Characterization and application of plasma mirror for ultra-intense femtosecond lasers

The femtosecond laser pulses reflected from the self-induced plasma mirror（PM） surface are characterized. More than two orders of magnitude improvement on intensity contrast both in nanosecond and picosecond temporal scales are measured. The far-field distribution, i.e., focusability, is measured to degrade in comparison with that without using a PM. Experiments on proton accelerations are performed to test the effect of the balance between degraded focusability and increased reflectivity. Our results show that PM is an effective and robust device to improve laser contrast for applications.

589-nm yellow laser generation by intra-cavity sum-frequency mixing in a T-shaped Nd:YAG laser cavity

To obtain high power 589-nm yellow laser, a T-shaped thermal-insensitive cavity is designed. The optimal power ratio of 1064- and 1319-nm beams is considered and the fundamental spot size distribution from the output mirror to the two laser rods are calculated and simulated, respectively. As a result, a 589-nm yellow laser with the average output power of 5.7 W is obtained in the experiment when the total pumping power is 695 W. The optical-to-optical conversion efficiency from the fundamental waves to the sum frequency generation is about 15.2% and the pulse width is 150 ns at the repetition rate of 18 kHz. The instability of the yellow laser is also measured, which is less than 2% within 3 h. The beam quality factors are Mx^2 = 4.96 and My^2 = 5.08.

Analysis of laser induced thermal mechanical relationship of HfO_2/SiO_2 high reflective optical thin film at 1064 nm

A numerical model is developed for the calculation of transient temperature field of thin film coating induced by a long-pulsed high power laser beam. The electric field intensity distribution of HfO2/Si02 high reflective （HR） film is investigated to calculate the thermal field of the film. The thermal-mechanical relationships are discussed to predict the laser damage area of optical thin film under long pulse high energy laser irradiation.

Femtosecond laser ablation of metals:a molecular dynamics simulation study

Using molecular dynamics (MD) methods combining with two-step radiation heating model, the mechanisms of ablation and the thermodynamic states at Ni surface under femtosecond laser irradiation are investigated. Simulation results show that the main mechanisms of ablation are evaporation and tensile stresses generated inside the target. The velocity of stress wave is predicted to be nearly equal to sound velocity. The rates of ablation at different fluences obtained from simulations are in good agreement with experimental data. Superheating phen omenon is also discovered.