We present a narrow linewidth frequency-doubled Cr:LiSAF laser with a 450- to 460-nm tunability and maximum repetition frequency (RF) of 63 kHz. Under a pump power of ∼900 mW, the fundamental wavelength could be tuned at the range of 883 to 1020 nm, with a maximum output power of 180 mW at 910 nm. The pulsed operation was achieved by using an acousto-optical modulator. An LBO crystal was adopted for intra-cavity frequency doubling and a maximum output power of 44.8 mW was obtained at 455 nm, indicating a slope efficiency of 11.2%. The spectral linewidth was <0.1 nm in the whole tuning range.
The effect of single junction GaAs solar cells irradiated by 808nm, 1070nm and 10.6um CW lasers is investigated. The results show that, as long as under the same laser coupling intensity, the damage modes of solar cells under different irradiation conditions are similar. With the increase of laser coupling intensity, the maximum temperature of solar cells rises, and the maximum power of solar cells shows a ‘stair-step’ decline. The multiple irradiation experiments of triple junction GaAs solar cells by 1070nm CW laser are carried out. The results show that when the laser intensity is more than 12.8W/cm2 , the performance degradation of solar cells will show a significant accumulation effect. In addition, the thermal sensitive damage factors are explored and verified. The results show that the maximum temperature and the duration of high temperature are sensitive factors for laser irradiation damage of solar cells.
To increase the lifetime of components in high power lasers and to study downstream light field the influence of the damaged optical components, numerical model of surface profile of damaged optical components were built with particle swarm optimization algorithm, and the relationship between the damage degree and the parameter of numerical model was analyzed. First laser irradiation experiment was carried out to acquire the damaged optical components. Then surface morphology was measured with Zygo interferometer system. With a typical Gaussian filter. A numerical model of one dimensional lineout of surface profile was established with particle swarm optimization algorithm. Numerical results shows that the model was valid with the particle swarm optimization (PSO) algorithm. The results also shows that there was a relationship between parameter of the model and the damage degree.
In order to study the mechanisms of thermal damage during laser machining in GaInP/GaAs/Ge tandem solar cells (TSCs), the spatial electroluminescence (EL) characterization on sub-cells pre and post laser irradiation was carried out. Results showed that post laser irradiation, the EL of GaAs middle cell increased to saturation in the damage zone, but decreased to zero at the rest part. A theory was put up to explain this phenomenon by using two-unit equivalent circuit model, and then verified through GaInP top cell spatial EL analysis. Conclusion was drawn that current redistribution induced by local shunt resistance decreasing in GaInP top cell was the main cause for the EL enhancement in GaAs middle cell.
Besides the excessive saturation effect, a new mechanism of temporary black screen of CCD camera induced by laser is found. The final output of CCD camera is the difference between the signals in effective pixels and optical black pixels. As the effective pixels of CCD camera are being irradiated by intense laser, many carriers induced by photo overflow from effective pixels into the optical black pixels. As a result, both the effective and optical black pixels will reach saturation, which makes the final output of CCD become zero. This effect has the same black screen phenomenon as the excessive saturation, and is named as pseudo-excessive saturation effect in this article.
Optical components in large aperture optical imaging system are susceptive to intense laser radiation. Optical band pass filter for spectra selection and nonlinear filter for intense laser blocking, are usually focal or near focal elements in imaging system, will more likely to be permanently damaged by high intense unwanted laser irradiating. In order to relate the optical imaging performance degradation to laser irradiating parameters, characteristics of the damage sites and so on, a test facility consisting of scaled electro-optical imaging system and standard imager evaluation system was constructed, and the linear spread function, modulation transfer function, signal transfer function, and noise power spectrum were obtained. Experimental imaging performance degradation law of damaged fused silica and colored glass filters were analyzed. Furthermore, some brief discussions on the imaging performance degradation mechanisms are also presented.
Three types of laser irradiating experiments on single junction GaAs solar cells with the same laser energy coupling intensity were carried out, which were irradiated by in-band (808 nm) and out-of-band (1.07 μm) continuous wave lasers respectively and simultaneously. On the basis of the changes of current-voltage characteristic curves of irradiated solar cells, the damage degrees could be divided into three stages which were gently, seriously and thoroughly damaged stages. The damage mechanism was studied from two aspects: output changes of solar cell equivalent circuit under different configuration settings, thermal analysis model. The results show that damage degrees of gently and thoroughly damaged stages is insensitive to irradiation intensity. However, the damage degree of seriously damaged stage is sensitive to irradiation intensity and this is regarded to be related to thermal decomposition of GaAs. Moreover, the increase of PN junction defects leads to performance degradation of irradiated solar cells. In conclusion, the thermal damage leads to the increase of PN junction defects, thus results in the performance degradation of cells.
KEYWORDS: Chemical species, Luminescence, Combustion, Liquids, Optical filters, Signal to noise ratio, Bioalcohols, Indium, Laser induced fluorescence, Signal generators
Nonlinear regime Two-line Atomic Fluorescence (NTLAF) is a promising technique for two-dimensional thermometry. A key challenge is seeding of indium atoms into flame. This work aims at investigating the mechanism of Indium LIF signal generation in a fuel-rich InCl3-ethanol premixed flame. Several types of images including natural emission of the flame itself, natural emission of CH, natural emission of OH, natural emission at 410 nm/451 nm of indium atom, and laser induced fluorescence at 410 nm/451 nm were obtained. The indium atom was generated in the flame front, and could survive in the post-flame zone for a while which is benefit for making NTLAF measurements. Further detail mechanism of fluorescence signals generation in InCl3-ethanol solution burning was investigated. The conclusion which probable to be drew is that to gain high NTLAF signals, the size of liquid droplets should be well controlled, neither to be too large nor to be gasified.
KEYWORDS: Sensors, Detector arrays, Laser applications, Optical testing, Signal attenuation, Signal detection, Pulsed laser operation, Mid-IR, Temperature metrology, Laser energy
The far field beam profile is of significant importance to the analysis of the atmospheric propagation effect and evaluation of the beam control capability, tracking and aiming precision of laser system. In the paper, technology of laser beam measurement such as mid-infrared laser detection at wide temperature range, power density attenuation, photoelectric and calorimetric compound method for laser measurement, synchronous detecting of multi-channel pulsed signal are introduced. A series of instrumented target with detector array are developed for laser beam power density distribution measurement at far field. The power in the bucket, strehl ratio, centroid and jitter of beam can be calculated from the measured results.
The discoloration and optical characteristics of the gold plating film under long-time high power laser irradiation are investigated. The fabrication process of gold plating on nickel underplate on rough surface of copper and aluminum alloy substrates is introduced. The measurement results of the diffuse reflectivity for the samples with different surface roughness indicate that roughness of the gold layer surface should be 4μm to obtain the maximum value of diffuse reflectivity. The discoloration and variation of diffuse reflectivity are experimentally studied under 2000W irradiation. The research results show that the discoloration and degrading of reflectivity are caused by the diffusion of Ni to the gold plating surface and forming NiO thin film due to the porosity of the gold film and high temperature treatment. A change of diffuse reflectivity related mechanism is described. Several plating solution recipes are used to eliminate the discoloration and mitigate the degrading of the reflectivity on gold surface.
A pulsed Er3+-doped ZBLAN fiber laser at 2.8 μm in fundamental-transverse-mode operation is reported. Stable gainswitching
is achieved with the repetition rate range from 0.5 to 10 kHz. The maximum laser pulse energy of up to 4.2 μJ
and pulse duration of 1.18 μs at a repetition rate of 10 kHz, yielding the maximum peak power of 3.5 W, has been
obtained. The maximum slope efficiency with respect to the launched pump power at 975 nm is determined to be 12.2%.
Pulse spikes occur by increasing the pump energy of larger than 75 μJ.
In this article, an overview of laser dazzling effect to buried channel CCD camera is given. The CCDs are sorted into staring and scanning types. The former includes the frame transfer and interline transfer types. The latter includes linear and time delay integration types. All CCDs must perform four primary tasks in generating an image, which are called charge generation, charge collection, charge transfer and charge measurement. In camera, the lenses are needed to input the optical signal to the CCD sensors, in which the techniques for erasing stray light are used. And the electron circuits are needed to process the output signal of CCD, in which many electronic techniques are used. The dazzling effects are the conjunct result of light distribution distortion and charge distribution distortion, which respectively derive from the lens and the sensor. Strictly speaking, in lens, the light distribution is not distorted. In general, the lens are so well designed and fabricated that its stray light can be neglected. But the laser is of much enough intensity to make its stray light obvious. In CCD image sensors, laser can induce a so large electrons generation. Charges transfer inefficiency and charges blooming will cause the distortion of the charge distribution. Commonly, the largest signal outputted from CCD sensor is restricted by capability of the collection well of CCD, and can’t go beyond the dynamic range for the subsequent electron circuits maintaining normal work. So the signal is not distorted in the post-processing circuits. But some techniques in the circuit can make some dazzling effects present different phenomenon in final image.
In this paper, an advanced non-mechanical beam aiming and pointing system is presented. Traditional beam steering is based on the mechanical systems. In the complex and expensive systems, beam jittering and many other problems are major limitations. However, beam steering with optical phased array (OPA) devices can realize agile beam control with random access pointing and high efficiency. Our system is mainly based on phased only spatial light modulators (SLM), which can realize beam steering non-mechanically. Based on the conventional one dimensional beam steering method of SLM, two dimensional beam steering method was presented at first in order to demonstrate the feasibility of the whole system. Then the whole system was tested. Our beam steering system can steer beam to a target which was moving at the speed of 3.8mrad/s within the field of view. The RMS error of the system was 0.0246mrad in one dimension, and 0.139mrad in two dimension respectively. Meanwhile the whole process was recorded by another camera in order to show the results.
Modeling of Tm-doped fiber lasers pumped with 793 nm, 1.6 μm and 1.9 μm is presented and compared. Output performance of three different pump schemes with active fiber length, pump power and output reflectivity is investigated. Numerical simulation shows that, with 793 nm pump, the cross relaxation process is of vital importance for high efficient operation of Tm-doped fiber laser. And, 1.9 μm pump scheme is more likely to offer even higher output compared with 793 nm pump and 1.6 μm pump.
The design and performance of a closed cycle, repetitively pulsed HF/DF laser is described. For obtained higher stable laser pulse energy and running frequency, discharge stability with different electrode profile and different gas circulation structure are researched. The functional relations of laser pulse energy with electric field strength (E) and gas mixture pressure (P) for various gas flow velocity are studied. It is shown that with preliminary optimized of the gas injection segment structure before pump region and optimal E/P conditions, maximal running frequency of 100Hz is obtained and operating stability keeps well. Under these conditions, the laser average power is 40W and peak power is 4MW.
The laser coupling effect of material is a fundamental factor to influence laser interaction with matter. The coupling coefficient, which is the material absorptance of the input laser energy, depends on the surface conditions of materials, such as temperature, incident angle, surface airflow, oxidizing environment, and so on. To measure the laser coupling characteristics of materials, two typical online measuring apparatuses were developed in our laboratory. One is based on a conjugated hemi-ellipsoidal reflectometer, which is suitable to measure the laser coupling coefficients of different temperature in vacuum and air environments. The other is based on an integrating sphere and a simple airflow simulator, which can be applied to online measure the laser absorptance of materials subjected to surface airflow. The laser coupling effects on two types of structural materials, which are alloy steels and composite materials, are given in this paper. With the conjugated ellipsoidal reflectometer, the laser coupling effects on a typical alloy steel are investigated in different temperatures under the vacuum and air environment, and the experimental results are analyzed. According the results, metal oxidization plays a key role in the laser coupling enhancement effects. Especially, when the metal is subjected to high power laser irradiation in the high subsonic airflow, metal oxidization which is an exothermic reaction enhances the laser damage effect and the convective heat loss is negligible. Finally, the laser coupling effects on a typical composite material subjected to airflow are studied by using the integrating sphere with an airflow simulator, and the experimental results of laser absorptance during the laser ablation are presented.
In this paper, Torrance-Sparrow and Oren-Nayar model is adopt to study diffuse characteristics of laser target board. The model which based on geometric optics, assumes that rough surfaces are made up of a series of symmetric V-groove cavities with different slopes at microscopic level. The distribution of the slopes of the V-grooves are modeled as beckman distribution function, and every microfacet of the V-groove cavity is assumed to behave like a perfect mirror, which means the reflected ray follows Fresnel law at the microfacet. The masking and shadowing effects of rough surface are also taken into account through geometric attenuation factor. Monte Carlo method is used to simulate the diffuse reflectance distribution of the laser target board with different materials and processing technology, and all the calculated results are verified by experiment. It is shown that the profile of bidirectional reflectance distribution curve is lobe-shaped with the maximum lies along the mirror reflection direction. The width of the profile is narrower for a lower roughness value, and broader for a higher roughness value. The refractive index of target material will also influence the intensity and distribution of diffuse reflectance of laser target surface.
A special waveform of CCD being irradiated by intense laser is explained and simulated. Its specialty is that reference level is altered and becomes equal with saturated data level, which can answer for CCD’s black video induced by laser and named as excessive saturation effect. Alteration of reference level has been explained by signal charges injection into the measuring well during reference time. In CCD, wells barriers are largely lower than channel stop. After that all transfer wells are crammed, many remained signal charges getting rid of clock’s control can be hold in channel, and move along it in thermal diffusion and self-induced drift. They can fill up the measuring well ahead of clock’s permission and alter reference level to saturated data level. Based on the explanation, the waveform is simulated on an equivalent circuit of CCD’s charge measurement structure, which is built on the platform of Multisim2001. The voltage sources and switches are used to manipulate the charge and discharge of a capacitor, which simulates the charge injection and resetting of measuring well. The clocks controlling switches represent the injection and reset clocks in CCD. To simulate clock’s impact on output, other capacitor is used to connect it to capacitor that represents the measuring well. The equivalent circuit is validated by the simulated normal waveform. Then, altering the clock and charging the capacitor ahead, the excessive saturation waveform is simulated, which validates the explanation to excessive saturation effect.
Detector is an important device for the far-field laser spot measuring apparatus in form of photoelectrical detector array,
for it acts as an optical-to-electrical converter in measure. Two working parameters of n-type HgCdTe photoconductor
are discussed in this paper. The fundamental electrical properties of n-type Hg1-xCdxTe material are summarized and
related to device performance parameters. It can be found that the dark resistance Rd and the voltage responsivity Rv are
closely bound up with temperature T and the alloy composition x, and the normalized calculating Rd-T and Rv-T
characteristic curves are in good agreement with experimental results at temperature below 20°C. And then the dynamic
responses of a detector under laser irradiation are studied by utilizing 2-D transient heat transfer model and empirical
formulas. Furthermore, experimental investigation on laser damage in PC-type HgCdTe devices is operated by a means
named 1on1. Detectable change in performance parameters has not been found under the irradiation of in-band laser, at
power density beyond the detector linear response zone, and time of 200s. When the power of irradiation strengthened,
the dark resistance increased, and the responsivity reduced. By observing the surface morphology of HgCdTe wafers,
calculating the compositions x from Rd-T characteristic, the causes for performance changing has been analyzed.
A system based on detector array is developed to measure the far-field temporal and spatial distribution and absolute
pulse energy density of the laser beam. In this experiment, the duration of the laser pulse is about 15ns, the repetition rate
is 400Hz, and the diameter of the far-field beam is about 60cm. The detector array is composed of 112 Si-PIN
photodiode detectors and arranged to be a disk with spatial sample rate of 0.4cm-1. Charge sensitive amplifiers and
baseline restoration circuits are used to collect photocurrent of the detectors, and current-input AD converters with
integrator front-end are used to digitalize the multi channel signals. The far-field laser beam profile is reconstructed with
the spatial sample data using special arithmetic of spatial interpolation. The system is capable for absolutely measuring
far-field energy density distribution of repetitively pulsed laser, with response wavelength between 400nm and 1100nm,
minimal detectable pulse duration of about 10ns, and energy density of 0.1-100μJ/cm2.
A fiber optic pulsed magnetic-field sensor based on Faraday magneto-optic effect is described in this paper. Its dynamic range is better than 70 dB within the nonlinearity of 5 percent and its noise equivalent magnetic flux density is about 1.5 by 10-6 T. By the method of frequency spectrum analyze, the frequency response characteristic of the sensor is measured and its -3dB bandwidth is about 200kHz. The experimental results indicate that the sensor can be used for pulsed magnetic field or current measurements.
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