The main drawback of diode laser array is the inhomogeneous intensity distribution in the far field. So the beam shaping
technology is very important in the application of laser diode array. This work present a novel beam shaping optical
system based on fly’s eye lens. The system can homogenize the diode laser array based on the multi-aperture beam
integrating theory. Such beam shaping system was designed by ray tracing method using ZEMAX™ Non-Sequential
Components analysis tools. The ray-tracing simulation shows that a 5 × 5 mm2 Top-Hat intensity profile was got at a
working distance of 40 mm and the homogeneity of the intensity distribution is better than 90%. And it is verified that
such beam shaping system is adapted for the aberrations of bars very well by simulation. Based on the design, a relative
experimental research on the beam shaping system for 5 bars LD stack is carried out. Through the beam shaping system
the laser diode power intensity is improved 4 times, light field distribution nonuniformity is less than 10%, and the
system coupling efficiency is more than 80%, which validated the engineering feasibility and applied value of this novel
LD array beam shaping system.
The analysis of scattering characteristics of diffractive optics based on Finite-difference time-domain method is
presented. And its scattering pattern along the surface is gotten. It shows that the scattering intensity in the discontinuous
surface is much higher than the continuous surface. This causes the decrease of diffractive efficiency. Binary optics with
multilevel relief can cause more scattering than micro optics with continuous relief, so it is not suitable for being used in
the situation where phase varies rapidly.
Efficient pumped coupling is one of the important technologies of diode pumped solid state laser system applying
end-pumped structure. This work present a novel pumped coupling optical system based on microlens arrays. In the
coupling system, the light of laser diode stack is incident on an imaging microlens array, that cuts the beam into a
number of beamlets. Subsequently these beamlets are overlapped in the pumped surface of laser media through an aspheric focusing lens. Then a high homogeneity pump field is realized. Furthermore, for different aspect ratios of the
homogenized spot two microlens arrays with crossed cylindrical lenses are used to match different pump field size. Such coupling system was designed by ray tracing method using ZEMAXTM
Non-Sequential Components analysis tools. The non-sequential raytracing simulation shows that a 5 × 5 mm2 Top-Hat intensity pump profile was got at a working
distance of 40 mm and the homogeneity of the intensity distribution is better than 90%. In comparison with the traditional coupling optical system homogenization by means of microlens arrays is more flexible and requires a reduced
number of optical components.
KEYWORDS: Thermal effects, Disk lasers, Thermal modeling, High power lasers, Finite element methods, Numerical analysis, Analytical research, Integral transforms, 3D modeling, Solid state lasers
The study of thermal effect plays an important role in the research and application of high power heat capacity laser.
FEM has been used to seek the numerical solution of heat conduction equation in the past study of laser thermal effect,
but the method can't describe the infection of laser material characteristic and pumping laser on the temperature
distributing and thermal stress distributing. And it is difficult to analyze the thermal lens effect, thermal birefringence
effect and their influences on the laser beam quality. The 3 dimensions heat conduction model under the cylindrical
coordinate is set up on the base of pumped structure of face-pumped disk laser. And the precise solution of transient
temperature field distribution is got through resolving the 3 dimensions heat conduction equation using
integral-transform method. On the base of this, the thermal stress field transient distribution is worked out. Using a
Φ50mm×18mm Nd:GGG disk laser as an example, the temperature distributing and thermal stress distributing under the
heat capacity model is calculated. The result and the numerical solution using FEM are a good match, and the theory
analyzing result is in accordance with the relative experiment result, so the thermal effect modeling and the resolving
method are proved to be correct. The research establishes the base of the further theoretical analysis of thermal effect
influence on the laser beam quality.
KEYWORDS: Semiconductor lasers, Thermal effects, Finite element methods, High power lasers, Optical pumping, Solid state lasers, Temperature metrology, Nd:YAG lasers, Laser cutting, Diodes
Laser diode (LD) pumped slab laser, as an important high average power solid-state laser, is a promising laser source in
military and industrial fields. The different laser diode pumping structures lead to different thermal effect in the slab gain
medium. The thermal and stress analysis of slab laser with different pumping structure are performed by finite element
analysis (FEA) with the software program ANSYS. The calculation results show that the face pumped and cooled laser
results in a near one-dimension temperature distribution and eliminates thermal stress induced depolarization. But the
structure is low pump efficiency due to the small thickness of slabs and the requirement to cool and pump through the
same faces. End-pumped slab laser is high pump efficiency and excellent mode match, but its pumping arrangement is
fairly complicated. The edge-pumped face-cooling slab laser's pump efficiency is better than face-pumping, and its
pumping structure is simpler than end-pumped laser, but the tensile stress on surfaces may initiate failure of the gain
medium so it is important to design so that the stress is well below the stress fracture limit. The comparison of the
thermal effects with different pumping structure shows that, the edge-pumped slab laser has engineering advantages in
high power slab laser's application. Furthermore, the end-pumped slab laser tends to get the best beam quality, so it is fit
for the application which has a special requirement on laser beam quality.
The thermal effect of fiber-coupled laser diode (LD) end-pumped Nd:YAG high-repetition-rate solid laser during the optical pumping are the important factor which affects the laser output characteristic and the system integrated performance. Aiming at a 2 W fiber-coupled LD end-pumped Nd:YAG laser, starting with the thermal conduction function, the numerical value of temperature steady distributing in the laser crystal is calculated applying the finite element method (FEM). Then the thermal stress in the crystal is obtained by calculation. And thermal lens effect are counted and analyzed. The study establishes the base of optimizing the design of laser to reduce thermal effect and improve the stabilization of laser output.
In the past, the measurement of MRTD, MTF of Infrared thermal imager usually used the eye subjective method. This method is more applicable, but its result is hard to decide and easy to induce dispute because of the effect of eyes’ subjective factor. The purpose of searching objective method is to eliminate these adverse factors and to present a unitary and objective judging standard. Nowadays several countries, denoted by English, have worked on this field and made big progress. China is on the starting step now. The key of objective measuring method is using computer to draw out the characteristics of infrared image and identify, then describe or judge the identified result.
In infrared imager system of using infrared focal sensor, for the responsivity heterogeneity among focal plan image elements and sensors and amplifiers can not be made in model of one to one, this kind of system asks for compensation of the heterogeneity of sensor response. Measuring the heterogeneity of focal plane image elements response accurately is the key to assure the quality of compensation. The article introduces a new method of measuring the heterogeneity of focal plane image elements response. It avoids the affect of black body radiate plane's spatial heterogeneity on the measuring result and gets higher measuring precision.
The objective measuring method of MRTD based on artificial neural network is using computer to judge the four bacilliform target image automatically and objectively replacing of human eyes' subjectively judgment. The characteristic vector of four bacilliform target image is extracted firstly before using computer to identify the image. The reasonable choosing of the characteristic vector not only affects the determination of the neural network, but also directly relates the identifying speed and accuracy (the judging efficiency of the neural network). The wavelet analysis of four bacilliform target image can well simulate the identifying procedure of the eye to four bacilliform target image. The experiment of identification of four bacilliform target image shows that using the total energy of the images of different frequency range as the characteristic vector is more suitable than using images average value, square-error, information entropy, etc.
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