Solid-state lasers are widely used in many applications. The LD pumping module is the power source of the laser system. A well-designed pumping light field can achieve high efficiency and high quality laser output. In this paper, a mathematic model of the side-pumping module is constructed. The light field of a single LD bar is tested and simulated with different parameters with the ray tracing method. Then the pump power distribution in the cross section of the LD array is analyzed, which indicates the absorption and distribution in the laser rod. An improved method by increasing the pumping sides is proposed to achieve higher pumping homogeneity. Simulation results show that the pumping homogeneity is improved. A pumping module is produced according to the design. After a small adjustment of the mathematic model, the test result of the rod cross section photos fits the simulation well. Then an optical resonant cavity with a Nd: YAG laser rod is set up. The laser with the beam quality near the diffraction limit is obtained. The LD pumping module can be used in high power MOPA laser systems. The improved mathematic model can be used to simulate and design side-pumped lasers in future.
With the rapid development of optoelectronic information technology, the infrared light source with the wavelength of 1~5μm has many potential application prospect in the field of spectroscopy, laser radar, remote sensing, laser communication and so on. The infrared laser can be obtained by many methods. Optical Parametric Oscillator (OPO) is one of the most important methods. It has the advantages of small size, light weight, stable performance, good reliability, high beam quality and the wide spectral range. In this paper, we design an OPO optical arrangement with the MgO:PPLN crystal which is pumped by a high repetition rate acousto-optic Q-switched Nd:YVO<sub>4</sub> laser. The crystal is fixed in a small case that the temperature could be precisely controlled. In the experiment, we heated the MgO: PPLN crystal to different temperatures. By adjusting the temperature, the relationship between the temperature and the output power is recorded. Theory analysis of the laser is given to illustrate the phenomenon. The effect on the output power and the transfer efficiency is detailed studied by varying the temperature of the MgO: PPLN crystal.
The application of the solid state lasers has been greatly expanded in many domains. The laser system is required to be highly integrated. In this paper, an integrated design scheme of laser diode pumped solid state laser is proposed. The size of the device is reduced by integrating the laser power source with LD pump module. The MCU and low-temperature drift drive circuit is utilized as the hard core. The simplified effective pre-stage DC-DC power source and a quasiresonant full-bridge temperature control circuit are designed. The deep negative feedback for the discharge control loop is concluded in the design. The TEC is used and the control accuracy is ±0.5℃ by the using of predictive PID. The ripple and rise time of the current waveform is tested and the stability of the power supply operated at 20Hz is verified by the load test. The experiment results reveal that this system has good load capacity and stability. Compared with the previous power supply system, this system is small and compact. The power supply efficiency is improved by more than 10% and the size of device is greatly reduced.
High-power lasers require tremendous power consumption, generate large heat loads in short time periods, and have challenging cooling requirements. A cooling system of phase change energy storage that reduced the volume and weight by many times was proposed. The system included a laser cooling circuit and a phase change cooling circuit. Designed a phase change cold storage heat exchanger, which was the closed heat exchanger that the cooling circuit consisted of multiple bundles of copper tubes and the phase change material was paraffin. Based on the experimental results, designed another open phase change energy storage cooling system with better performance. Comparisons of these two types of phase-changing heat exchangers showed that choosing water as phase-changing material can get more accurate temperature control.
High order harmonics is generated in a modulated slab waveguide which is filled with helium when a femtosecond laser is focused into this kind of waveguide. The modulated slab waveguide is used to implement quasi-phase matching of high order harmonics so that an obvious increase of the high harmonics yield at wavelengths close to the cutoff region was observed. High order harmonics generated in modulated waveguides with a period of 0.8mm and a period of 0.5mm respectively were compared. The results show that the shorter the period of the modulated slab waveguide is, the higher order high harmonics with phase mismatch we can compensate.
Laser decoy is widely used in the field of electro-optical countermeasures, against laser guided semi-automatic weapons. Decoy laser usually includes a laser light source with specific wavelength and signal, whose energy distribution has Lambertian reflection characteristics. With a 633nm laser source, a fibre and a diffusive module, a homogeneous field laser was illustrated, which was generated through high-density colloidal dispersion to get diffused. By optimizing the fibre and structure parameters, the laser light energy utilization was improved while maintain light field uniformity. Additionally, the flat field system was designed and tested using high reflectivity PTFE material, with a reflectivity of 97%. A developed Lambertian light source system for reference-based Laser decoy was established, whose non-uniformity was lower than 0.3%. The results showed that the Lambertian light source system could meet the requirement of Laser decoy, and needed to be improved in near infrared.
We demonstrated a large face pumped double-sided liquid cooling Nd:YAG slab laser. The pump light incident from the large surface of the crystal, which are cooled by high-speed flowing cooling water, while the laser beam incident on to the end face, and travels in ZigZag path along the long direction in the crystal. The flat-flat resonant cavity was built, and the output coupler transmission was 30%. The Nd:YAG slab crystal with trapezoidal shape was used as the gain medium, the size of which was 190mm×12mm×4mm, one of the surfaces of 190mm×12mm was coated with antireflection film for 808nm and another was coated with reflection film for 808nm, and the end faces of 4mm×12mm were coated with antireflection film for 1064nm, the doping concentration of Nd<sup>3+</sup> ion was 1.0at.%. The CW LD array and QCW LD array were used as the pump source to pump the slab crystal, the light emitting surfaces of which have the same size, and the pumping light passed through the pump windows made off used silica and incident into the crystal. Under CW LD pump, the maximum of 420W laser output was gotten, and under QCW LD pump, the maximum of 502W laser out put was gotten. Due to the much higher peak power of QCW laser diode, the small-signal gain was much higher, and induced the optical efficiency of QCW pumping system was much higher, and its thermal effect was relatively smaller because of the high extraction efficiency.
The effects of laser irradiation on materials include thermal ablation, shock and radiation, where the thermal ablation is the major one in industrial application. When the laser beam irradiates the target, the temperature rises rapidly from the outside in until reaching a certain temperature. The material is melted even gasification. The steam expands and splashes, while washing away the molten material in liquid or solid state and forming pits or perforation. The effect of thermal ablation is related to the parameters of laser source, the external environment parameters and the material parameters. The parameters of the laser source include the wavelength, power density, irradiation time, CW or pulse and the pulse length. The short pulse laser mainly ablated the material by reaching the threshold of power density, while the long pulse laser by reaching the threshold of energy density. In this paper, a dual pulse length method is discussed and theoretically analyzed. A dual pulse length laser with nanosecond and microsecond pulse length is used. The experiment is carried on in three situations: only microsecond laser, only nanosecond laser and both. Experiment results show that the short pulse laser is much better than the long pulse laser under the same average power condition. When the dual pulse width laser is irradiated and the exposure time is accurately matched, the effect is greatly improved and the damage threshold is decreased by one order of magnitude.
A growing number of applications are calling for the compact high energy laser sources. In the last decade, significant progress has been made in the area of solid state lasers especially fiber lasers. The solid state laser is widely used in the processing industry, telecommunication systems at present. However, thermal effect, nonlinear effect and the damage of optical components limits the output power. We present a laser coherent combining technique based on heterodyne method in all-fiber feedback format. In this technique the feedback signals are coupled and transferred by fiber to simplify the system, while all factors of the signals such as the wavefront distribution, polarization state, power ratio of the sub-beams and the reference beam need to be considered and strictly controlled. Compared with the previous system, this technique brings another important advantage: Only the coupling side should meet stringent tolerance toward collimation. Phase detection for laser interferometry, phase control of sub-lasers is theoretically analysis and simulated to reveal the system control bandwidth, phase precision. A high speed phase detection circuit and a phase control circuit are developed. Proof of concept of this technique is experimentally demonstrated at 1.06μm. The experiment setup is shown. Stable results are obtained. The peak power rises up while the theoretical result is 2. Experiments reveal the validity of the technique in nanosecond pulse laser coherent combining.
Thermal effect is a plateau that limits the output of high-power, high beam quality laser, and thermal effects become worse with the increase of pump power. We can reduce the effects caused by thermal effects from pumping, laser medium shape, cooling method and other aspects. In this article, by using finite element analysis software, the thermal effects between Nd:Glass and Nd:YAG laser crystal was analyzed and compared. The causes of generation for thermal effects, and factors that influence the distribution in laser medium were analyzed, including the light source, the laser medium shape and the working mode. Nd:Glass is more suitable for low repetition frequency, high energy pulsed laser output, due to its large size, line width and so on, and Nd:YAG is more suitable for continue or high repetition rate laser output, due to its higher thermal conductivity.
The laser beam is attenuated, broadened, defocused and may even be deflected from its initial propagation direction as it propagates through the atmosphere. It leads to the decrease of the laser intensity of the receiving surface. Gauss beam is the fundamental components of all possible laser waveforms. Therefore, research on the transmission of the Gauss laser has far-reaching consequences in optical communication, weaponry, target designation, ranging, remote sensing and other applications that require transmission of laser beams through the atmosphere. In this paper, we propose a laboratory simulation method using multi-phase screen to calculate the effects of atmospheric turbulence. Theoretical analysis of Gauss laser transmission in the atmosphere is given. By calculating the propagation of the Gauss beam TEM00, the far field intensity and phase distribution is shown. By the given method, the optical setup is presented and used for optimizing the adaptive optics algorithm.
Digital holography is widely used as a high resolution metrological technique in many domains. As a coherent imaging
method, the speckle noise is inherent in the system and degrades image quality and optical resolution. An improved
fiber-space-hybrid lensless Fourier-transform digital holography system is proposed. Multiple holograms are recorded
with different oblique illumination. All hologram are reconstructed individually using the same program and each
reconstructed image has a different speckle pattern. The oblique illumination system is optimized by an automatic two
dimensional scanning of the fiber tip. Thus only a limited illumination area of light spot is demanded. By averaging the
reconstructed images, the speckle noise of the reconstructed image is reduced. We demonstrate the effectiveness of the
technique experimentally. The proposed system is convenient and practical. It can lead to a high quality result
The expressions for the reconstructed field from the sample of the diffracted wave, which is produced by illuminating an object, are found by use of different diffraction integrals in the digital holography. The numerical reconstruction methods that truncate and sample this field are compared in overlapping quality, accuracy, pixel resolution, computation window, and speed. The fast Fourier transform (FFT)-based direct integration method for the Fresnel integral and the modified FFT-based direct integration method for the Rayleigh-Sommerfeld integral have similar overlapping quality and can flexibly control pixel resolution and computation window size. Meanwhile, the FFT-based angular spectrum method is superior to the FFT-based convolution method in accuracy and speed. The experimental results are presented to verify these consequences.
Digital holography combines the advantages of the optical holography and the digital image processing
as a method for recording and reconstructing amplitude and phase of a wave field. Traditional
reconstruction algorithms can only obtain image with the fixed pixel size. By directly discretizing the
Reyleigh-Sommerfeld (RS) integral formula, a new reconstruction algorithm is proposed. Experiment
result shows that the reconstruction pixel size and pixel number can be controlled with the proposed
Digital holography is a whole-field, non-contact, and highly sensitive interferometric imaging and testing technology. It
is more suitable for microscopic measurement owing to digitalization and flexibility in holograms recording, storage,
reconstruction and transmittance. This paper analyzes the factors which lead to the phase aberrations in the off-axis
lensless Fourier transform digital holography firstly. Then a method, which is obtained by borrowing ideas from T.
Colomb, is presented to correct the phase aberrations automatically during the numerical reconstruction. This is
implemented by multiplying a phase mask directly with the reconstructed wave field. The phase mask is obtained by an
iterative procedure computing automatically without the pre-knowledge of the physical parameters, such as the off-set of
the reference point source and the recording distance. This method enables one to reconstruct the relative correct and
accurate phase-contrast image, even in the presence of the noise, which is needed to be smoothed by a median filter. In
order to achieve an accurate phase image, the procedure described here is applied iteratively, starting from the initial
values provided by the first evaluation. We present and analyze the simulation results of the phase images based on a
special three-dimensional micro object. The results show that for a weak noise the above method is very effective; while
for strong noise the common phase-unwrapping method must be applied. This indicates that it is very important to record
high quality hologram and to suppress the noise in phase data.