A nanometer-resolution displacement measurement instrument based on tunable cavity frequency-splitting method is presented. One beam is split into two orthogonally polarized beams when anisotropic element inserted in the cavity. The two beams with fixed frequency difference are modulated by the movement of the reflection mirror. The changing law of the power tuning curves between the total output and the two orthogonally polarized beams is researched, and a method splitting one tuning cycle to four equal parts is proposed based on the changing law, each part corresponds to one-eighth wavelength of displacement. A laser feedback interferometer (LFI) and piezoelectric ceramic are series connected to the sensor head to calibrate the displacement that less than one-eighth wavelength. The displacement sensor achieves to afford measurement range of 20mm with resolution of 6.93nm.
Star extraction is the essential procedure for attitude measurement of star sensor. The great challenge for star extraction is to segment star area exactly from various noise and background. In this paper, a novel star extraction method based on Modified Water Flow Model(MWFM) is proposed. The star image is regarded as a 3D terrain. The morphology is adopted for noise elimination and Tentative Star Area(TSA) selection. Star area can be extracted through adaptive water flowing within TSAs. This method can achieve accurate star extraction with improved efficiency under complex conditions such as loud noise and uneven backgrounds. Several groups of different types of star images are processed using proposed method. Comparisons with existing methods are conducted. Experimental results show that MWFM performs excellently under different imaging conditions. The star extraction rate is better than 95%. The star centroid accuracy is better than 0.075 pixels. The time-consumption is also significantly reduced.
A novel high sensitivity refractive index sensor based on balloon-like singlemode-tapered multimode-singlemode (STMS) fiber structure has been proposed and experimentally demonstrated. Combining the tapering and bending endows the proposed sensor with large evanescent field, resulting in high sensitivity. Experimental results show that the proposed sensor has an average sensitivity of 1104.75 nm/RIU (RI Unit) in the range of 1.33-1.41 and a maximum sensitivity of 3374.50 nm/RIU at RI of 1.41.
The progress on laser feedback interferometry technology is reviewed. Laser feedback interferometry is a demonstration of interferometry technology applying a laser reflected from an external surface, which has features including simple structure, easy alignment, and high sensitivity. Theoretical analysis including the Lang–Kobayashi model and three-mirror model are conducted to explain the modulation of the laser output properties under the feedback effect. In particular, the effect of frequency and polarization shift feedback effects are analyzed and discussed. Various applications on various types of lasers are introduced. The application fields range from metrology, to physical quantities, to laser parameters and other applications. The typical applications of laser feedback technology in industrial and research fields are discussed. Laser feedback interferometry has great potential to be further exploited and applied.
A glass birefringence measurement system utilizing the reflective laser feedback (RLF) effect is presented. The measurement principle is analyzed based on the equivalent cavity of a Fabry–Perot interferometer, and the experiments are conducted with a piece of quartz glass with applied extrusion force. In the feedback system, aluminum film used as a feedback mirror is affixed to the back of the sample. When the light is reflected back into the cavity, as the reinjected light is imprinted with the birefringence information in the sample, the gain and polarization states of the laser are modulated. The variation of optical power and polarization states hopping is monitored to obtain the magnitude of the stress. The system has advantages such as simplicity and low-cost with a precision of 1.9 nm. Moreover, by adjusting the position of the aluminum, large-area samples can be measured anywhere at any place.
Diode-pumped solid-state lasers are high efficiency, long lifetime, compact and reliable, so they have been covering a wide
range of applications. Thermal effect is a major limiting factor in scaling the average power of high-power solid-state lasers,
so it is a critical issue in designing diode-pumped solid-state lasers. The uniform pump intensity distribution in laser rod
can weaken the influence of thermal effects in laser, and the research of improving the pump distribution uniformity has
attracted a great deal of attention. People usually establish a model of single diode-bar pumped laser rod to calculate the
distribution. However, for diode-array pumped high-power lasers, the model is limited and has deviation with the actual
pump distribution, which cannot reflect the real working conditions in the laser.
In this paper, the theoretical model of diode-array pumped laser rod is built. Based on the actual working environment of
diode-array side-pumped Tm:YAG laser rod, the expression of pump intensity distribution in the laser medium is deduced.
Additionally, the influence of total pump power, pump structure, Tm:YAG rod characteristic parameters and pump beam
radius on pump intensity distribution are simulated and analyzed. Moreover, the parameters are optimized in order to
obtain the optimistic results which are efficient to improve the uniformity of pump distribution. The results show that when
the pumping distance from diode-array to the rod’s surface is 3mm, the distance between two rows of diode-bars is 1mm,
the absorption coefficient is 330m<sup>-1</sup>,the pump beam width is 2.5mm,the pump intensity distribution of five-way pumped
laser rod is improved, and then the thermal effects could be weakened. The presented results can provide theoretical
guidance to design and optimization of high-power lasers.
In the Tm<sup>3+</sup> doped YAG crystal, the Tm<sup>3+</sup> ions are excited into the <sup>3</sup>H<sub>4</sub> state from <sup>3</sup>H<sub>6</sub> state by absorbing pump radiation at ~ 785 nm, and the ions then relax down to the upper lasing level <sup>3</sup>F<sub>4</sub>. The laser radiation takes place between the lower Stark level of <sup>3</sup>F<sub>4</sub> and the higher Stark level of <sup>3</sup>H<sub>6</sub>. The considerable phonon broadening and high multiplicity of the Stark levels of the 4f electron provides tunability from 1.87 to 2.16 μm. We presented an analysis for the performance of side pumped quasi-three-level laser oscillators. Taking into account reabsorption loss, we present a theoretical model studies of quasi-three-level laser with particular attention given to the Tm:YAG laser. Equation for Tm:YAG quasi three-level laser system is founded, and a formula of the threshold pump power of the laser is described. The threshold pump power with different emission wavelengths versus the transmission of the output coupler is discussed, and we also analysis the influence on the threshold pump power with different emission wavelengths affected by the crystal length. With the same pump power, a lower transmission of the output coupler would result in a higher intracavity intensity. As a result, the lower laser sub-level within <sup>3</sup>H<sub>6</sub> ground state manifold has higher reabsorption loss and therefore, the higher Stark sub-level within <sup>3</sup>H<sub>6</sub> ground state manifold has a lower laser threshold and longer laser wavelength.
High-power laser systems are getting more and more widely used in industry and military affairs. It is necessary to develop
a high-power laser system which can operate over long periods of time without appreciable degradation in performance.
When a high-energy laser beam transmits through a laser window, it is possible that the permanent damage is caused to the
window because of the energy absorption by window materials. So, when we design a high-power laser system, a suitable
laser window material must be selected and the laser damage threshold of the window must be known.
In this paper, a thermal analysis model of high-power laser window is established, and the relationship between the laser
intensity and the thermal-stress field distribution is studied by deducing the formulas through utilizing the
integral-transform method. The influence of window radius, thickness and laser intensity on the temperature and stress
field distributions is analyzed. Then, the performance of K9 glass and the fused silica glass is compared, and the
laser-induced damage mechanism is analyzed. Finally, the damage thresholds of laser windows are calculated. The results
show that compared with K9 glass, the fused silica glass has a higher damage threshold due to its good thermodynamic
properties. The presented theoretical analysis and simulation results are helpful for the design and selection of high-power
The combination of volumetric heating of the laser material by the absorbed pump radiation
and surface cooling required for heat extraction leads to a no uniform temperature distribution in the
rod. With the coactions of pump field and coolant, the temperature gradient is formed within laser
working medium, and then the thermal effects including thermal lens, thermal stress birefringence, etc.
They all seriously restrict the output characteristics of laser. The uniform temperature field distribution
in laser working medium weakens the influences of thermal effects in laser. The thermal effect of
Tm:YAG laser generated by laser-diode pumping the Tm:YAG crystal is analyzed. After considering
the quasi three-level structure of the crystal and the distribution of transmission power in the cavity, a
more actual temperature field in the crystal is obtained by revamping the heat conversion coefficient.
The thermal effects mechanics were analyzed at first, and then the physical and mathematical thermal
analysis models were established based on the theoretical knowledge of thermal effects in LD pumped
Tm:YAG laser. The method can be applied to the laser thermal effect research of quasi three-level. The
analysis and the result can be referred to the thermal effect research of the solid state laser end-pumped
by the LD and the optimal design of resonant cavity.
The output window of a high-power laser system is vulnerable to damage, and this is the main limiting factor on the power scaling and structure integrity of the laser system. In endeavoring to obtain higher output powers from the laser system, the impact of the thermal and mechanical effects and the damage mechanism of the output window must be considered. In order to study these issues, a thermal model of the laser window is established based on the heat transfer and thermoelastic theories, and the expressions for the transient thermal and mechanical stress distributions of the output window are deduced in terms of the integral-transform method. Taking the infrared quartz window material as an example, the temperature and mechanical field distributions of a high-power all-solid-state 2-μm laser system window are simulated, and the laser-induced damage mechanism is deeply analyzed. The calculation results show that the laser window-induced damage is mainly caused by melting damage when the temperature exceeds the melting point of the material. The presented theoretical analysis and numerical simulation results are significant for the design and optimization of high-power laser windows.
For the echo signals of Satellite laser altimeter, the leading source of noise is the background radiation noise, which mainly comprises the reflection of sunlight by the targets and the atmospheric scattering of sunlight. This paper deals with a theoretical study on the reflection and atmospheric scattering of sunlight. And on the basis, we calculate and simulate the irradiance of extraterrestrial solar spectrum and the respective effects of path zenith angel, solar zenith angle and ground diffuse reflectance on the solar atmospheric radiance, concluding the corresponding relationship between background radiation noise and these parameters, which provides a theoretical basis for the improvement of Satellite laser altimeter.
With the development of Charge Coupled Device (CCD) technology, the method to measure the optical system’s resolution with the machine sight has been applied widely, which can overcome the factor of subject error that will exist when adapting human being’s eyes to measure the resolution. With the radical target to measure the optical system’s resolution, it has many merits such as the measuring equipment is simple and the operation method is convenient. The measuring process is realized with a collimator and a CCD camera through adopting necessary image processing methods in the paper. The matching problem between the machine sight and the human being’s eyes when judging the optical system’s resolution is analysed firstly in the paper. And the critical contrast is got, which should be adopted when applying the machine sight to measuring the optical system’s resolution. Next step is to find where the resolution is nearest to the critical contrast in the target image. With the method present in the paper, we get it. So the resolution of the tested equipment can be figured out. Through contrastively analyzing the resolution data which is obtain with conventional method and with the method presented in the paper, it shows that the method to measuring the optical system’s resolution with radical target in the paper is viable completely.
Seeker is the key component in the laser guided weapons. Although the seeker has many anti-jamming measures such as the narrowband filter in the front of the seeker and the tracking gate processing circuit in signal processing part, and these anti-jamming measures are always effective for the low power jamming laser. As far as the high power laser which can pass though the filter is concerned, it is easy to make the detector saturate, which will lead the seeker into losing the capturing and tracking capability for the target. In the past ten years, the applied research of organic nonlinear materials which is according to the optical limiting effect has had great development in the laser technology field. And some of these materials have been put into practicability phase. This kind of materials is characterized by its wide absorption spectrum, obvious nonlinear effect and quick response speed, all of which excel the mineral. If this kind of materials can be applied into the laser seeker, it will remedy the laser seeker's defect that its protective capability is weak for the high power jamming laser. The whole applied scheme is present in this paper. And the anti-jamming capability of seeker is analysed constructively before and after the organic matter is applied in the laser seeker. The result indicates that this kind of method is viable in theory.
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.
Position sensitive detector (PSD), which bases on the lateral photoelectric effect, is a novel position detector coming out in recent years. It can be applied to detect angle, height, distance and movement. In this paper, the development, principle, structure and its application in an active range finding system have been given.
The principle of measuring passive incident laser beam's space direction by use of the PSD (photoelectric site detector) and structural design of system are presented. Theory and experiment show passive incident beam's space direction can be determined accurately and quickly.
In a Faraday optical-fiber current sensor, it has many kinds of linear double refraction inevitably because of the circular degree error of the optical fiber, deformation of pressure, temperature effect and other reasons. It results in an additional phase difference, which will affect the detecting sensitivity and even decrease it to zero. A new method that can eliminate the effect of linear double refraction is offered in this paper with phase conjugate device after analyzing the foundational operation principle of the Faraday optical-fiber current sensor and the effect of the linear double refraction.
In the modern weapon systems, more and more the TV tracking systems have been widely used. It has more good characteristics than infrared tracking, laser tracking, radar tracking. When the high-power or high-energy laser irradiates the CCD video camera, it will be disturbed or damaged and lead to the TV tracking system damage, such as losing the tracking target. In the paper, the laser damage ofthe CCD has been studied theoretically and experimentally.
The factor M<SUP>2</SUP> is a new parameter to describe the laser beam quality, it can characterize the propagation of the fundamental and higher-order mode beam quantitatively. An automatic measurement system has been developed which is capable of measuring the laser beam quality factor M<SUP>2</SUP>. In the paper, the concept and the measurements of the factor M<SUP>2</SUP> are mentioned, the measurement results and tolerance limits are given.
In order to measure and control the illuminance of a partial environment, a measuring and control system has been established. In this paper the designing principle of the system, the major structure and the flowchart of software will be introduced.
Based on the photoconductive effect of the semiconductor, a photoconductive switch (PS) has been made. At the high dc bias voltage, an electrical pulse with nanosecond rise times, high-power and high-voltage has been generated. In the paper, the physics of the PS under high voltage is discussed.
The peripheral vision display system (PVDS) presents the pilot with a gyro stabilized artificial horizon projected onto the instrument panel by means of a red laser light source. The pilot can detect changes to aircraft attitude without continuously referring back to his flight instruments. The PVDS effectively applies the peripheral vision of the pilot to overcome disorientation. This paper gives the principles of the PVDS, according to which, we have designed the PVDS and used it for aviation medicine.