We develop a new algorithm to evaluate the thermal features of a rubidium-vapor cell and a cesium-vapor cell pumped by the laser diode. The theoretical model is based on the principles of both heat transfer and laser kinetics. The obtained population density distribution and the radial temperature distribution are analyzed for both types of cells. It is thought that the theoretical results are logically reasonable and the mathematical precision is satisfactory in designing a real diode-pumped alkali laser (DPAL). The methodology is valuable in the construction of a high-powered DPAL in the future.

We focus on the need for azimuthal orientation angles of a system. If one azimuthal orientation angle is a function of other angles and these angles turn independently by the same axis, the sum of the partial differential of the function to the other angles is 1. We use this property of the azimuthal orientation angles turning by the same axis of the system to analyze the experimental phenomena of the terahertz polarization, and then quantum theory is used to explain the experimental phenomena.

In order to test mild aspheric surface directly without other null optics, the digital plane method is proposed. When departure of the tested aspheric surface is mild, a sphere mirror can be used as the reference surface. The phase distribution can be measured swiftly by the digital interferometer. The surface error can be -obtained by subtracting the theory wavefront error (the value of the digital plane) from the phase data and eliminating the translation errors through least-squares fitting. The basic principle and theory of this method are analyzed and researched, and the testing model and flow chart are established. Meanwhile the experiment is carried out with a mild aspheric mirror by this method, the PV and RMS of the surface error are 0.173l and 0.018l (l is 632.8 nm), respectively. We also design and make a null corrector to the asphere for contrast, the differences in PV and RMS error between them are 0.026l and 0.001l, respectively.

The integrated manufacturing technology is introduced to improve the imaging quality of an off-axis -three-mirror anastigmatic (TMA) system. With the integration of system design, manufacturing of highly -precise optical elements, simulation and evaluation capabilities of the manufactured system, and testing and -alignment with the same fiducial, we can efficiently and precisely achieve high quality of an optical system. In order to prove the efficiency of this technology, we design an off-axis TMA system with MTF invariance better than 0.50 (57 lp/mm), and manufacture the aspherical surfaces of this optical system with surface figure error better than l/50 (RMS, l = 632.8 nm). We develop an interface software named MetroMax to achieve the connection between the final surface figure and the optical design software. The MetorMax also forecasts the imaging quality of the system, and guide us in aligning the system with a same fiducial with the whole field of view approached l/14 and MTF invariance better than 0.95. To confirm the imaging system after integrated manufacturing, we test the system on the ground and orbit; the result proves effective improvement in the imaging quality of the optical system.

High-power laser system has a requirement for the medium and low spatial wavefront errors of the transmitted wavefront of the spatial filter, which is a spherical lens with long focal length (> 10 m) and large aperture (> 400×400 (mm)). Two interferometric methods are analyzed and compared for testing the medium and low spatial wavefront errors of the long focal length lens with an instantaneous interferometer, using large -aperture plane mirror and concave mirror as retroflectors, respectively. The two kinds of beam path -arrangements are designed using ray tracing method. Wavefront aberration and modulation transfer function are used as merit functions. The reason for their different ability to test the wavefront is also analyzed. To evaluate the -feasibility of test methods, tolerances analyses are performed to determine the tolerances demanding the fabrication and assembly of each optical element. It is proved that a relatively short optical path with a large aperture concave mirror is satisfied for testing the medium and low spatial wavefront errors of the transmitted wavefront of the spatial filter.

In order to study the beam cleanup effect of the stimulated Raman scattering (SRS) in the graded-index multi-mode fiber (GIMF), a continuous wave all-fiber laser at 1117.8 nm and a pulsed fiber amplifier at 1064 nm are built up as the seed and pump source in the Raman fiber amplifier (RFA). In unseeded SRS process, a pump beam with M.2x = 6.7 and M.2y = 6.7 is transferred into a Stokes beam with M.2x = 1.5 and M.2y = 1.7 in the multi-mode fiber with a 62.5 μm graded-index core (numerical aperture =0.29). In the RFA, a seed light with M.2x = 6.7 and M.2y = 7.3 is amplified to a signal light with M.2x = 1.8 and M.2y = 2.0. The experimental results are explained by the simulation on the mode evolution during SRS procession and Raman amplifica-tion in the GIMF. The results show that both the SRS and Raman amplification effect in the GIMF have beam cleanup effect.

A Q-switched Er-doped all-fiber laser, based on a single-walled carbon nanotube saturable absorber (SA) is constructed. The SA with a modulation depth of 8% is prepared using a special chemical-corrosion method. Furthermore, the SA is introduced to an Er-doped all-fiber laser, and Q-switching is obtained successfully. The repetition rate of the Q-switched laser can be tuned continuously from 128 to 278 kHz with pulse widths from 1.92 μs to 488 ns. The maximum output power is 13.1 mW.

Distributed feedback fiber lasers with multiple phase shifts are fabricated and investigated. Single longitudinal mode lasers with single polarization are obtained by the structure design with two phase shifts. No obvious differences in laser performance, including pump threshold, slope efficiency, relative intensity noise, spectral linewidth, and polarization state, are observed for the presented distributed feedback fiber laser structures with different phase shift locations.

We demonstrate a narrow linewidth 1881 nm Tm:YAG ceramic laser that combines the advantages of in-band pumping at 1617 nm and volume Bragg grating as a wavelength selection device. With an output coupler of 5% transmission, a maximum output power of 200 mW is obtained at 1881 nm with a linewidth of 0.2 nm.

We report a diode-end-pumped Q-switched YVO4/Nd:YVO4/YVO4 self-Raman second-Stokes laser at the wavelength of 1764 nm. With the incident pump power of 32 W and the pulse repetition frequency of 20 kHz, the maximal average output power at 1764 nm is up to 1.18 W, with the corresponding optical conversion efficiency of 3.69%. The highest pulse energy and peak power are 59 mJ and 31.7 kW, respectively.

In order to research the influence on the beam transmission properties due to the different time intervals in the high-power pulsed transversely excited atmospheric CO2 laser with unstable resonator, the finite element analysis of thermodynamics instantaneous method are adopted to analyze the mirror thermal deformation irradiated by the high-power laser beam. The mirror thermal deformation is fitted by Zernike polynomials. Then the angular spectrum propagation theory of diffraction is used to calculate the far-field transmission properties. The simulation results show that with the decrease in the time interval between each pulse, the mirror temperature and thermal deformation gradually increase, and peak power and the average energy density decrease, and beam broadens. With the 500 Hz repetition rate relative to the 10 Hz repetition, the peak intensity decreases almost 40%; the optical spot broadens about 60%. When the repetition rate is larger than 100 Hz, the surface of mirror will have obvious deformation, which will cause apparent degradation in the optical beam quality for the far-field transmission.

We propose a method of cascading multiple nonlinear optical loop mirrors (NOLMs) in the laser cavity to enhance the single pulse energy in mode-locked fiber lasers. A geometrical description is used to engineer the transmittance curve of the effective mode locker in the cavity to enlarge the threshold of triggering multipulse transition. A full vector model of Ginzburg–Landau equation is adopted to model the pulse evolution in the cavity. Results show that, with the cascading NOLMs configuration, the single pulse energy and peak power can be increased by 170%–188% comparing with that in single NOLM cavity.

To study how laser pulse wavelength will affect the damage characteristics of optical elements with different degrees of contamination, we compare the extent of damage on optical glass between nanosecond pulsed laser of 1064 and 355 nm wavelength, respectively, and reach the following conclusions: the surface quality of clean optical elements determines its own anti-laser damage capability; the damage probability of optical sample caused by ultraviolet radiation-induced organic contamination is much higher than the infrared radiation-induced one; and contaminated metal particles can lower damage threshold of optical elements by 2–3 times.

Random distributed feedback Raman fiber laser is a convenient method to generate laser without using cavity mirrors. We show for the first time to the best of our knowledge a 10-W-level random fiber laser operated at 1178 and 1212 nm (1.2-μm range). The power character and features in time domain and spectrum are presented.

In this article, we analyze the factors that limit the output power increase for photonic crystal fiber lasers and set a theoretical model to calculate the maximum extractable power of ytterbium-doped photonic crystal fibers. Numerically, when the diameter of core is 76-\mu m and the pumping intensity is 0.21 W/(\mu m2×Sr), the output of pure silica and ytterbium-doped photonic crystal fiber lasers is 100-kW, considering the technology for the time being. The main limitations of power scaling are facet damage and thermal self-focusing. In case of the strict single-mode operation condition, the maximum extractable power is 100-kW when the numerical aperture is 0.05. Considering the strict single-frequency operation condition, the maximum extractable power of both pure silica and ytterbium-doped photonic crystal fiber lasers is 1.65-kW, where the main factor is stimulated Brillouin scattering effect. Compared with the previous results, the increase in the maximum extractable power depends on three parameters: the availability of high-brightness pump diodes, the endless single-mode characteristic of the photonic crystal fiber, and the high doping density which lead to efficient absorption coefficient of pumping light. Finally, we simulate numerical aperture that influences the maximum power of photonic crystal fiber lasers and compare the difference in maximum output power of photonic crystal fibers and double-cladding fiber lasers in single-frequency condition.

A speckle pattern is observed when a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser is homogenized by a diffractive optical element (DOE) due to its high spatial coherence. Therefore, a Nd:YAG laser homogenized by a DOE was previously considered not suitable to pump a Ti:sapphire laser amplifier. However, we show by experiment and simulation that the speckle structure does not manifest itself in the final amplified Ti:sapphire laser beam. By using the homogenizer, a smooth distribution of the amplified laser beam is obtained. No degradation of the energy, the wavefront, and the temporal characteristics of the amplified laser beam is observed.

The combination of lens and pinhole limits the enhancement of the laser output power in the high-power laser system. Low-pass spatial filter without focusing can surmount the drawbacks of the pinhole filters. The low-pass spatial filters based on multilayer dielectric film are analyzed and their filtering performances are validated. The non-focusing low-pass spatial filter is successfully explored to substitute for the focusing one. The design method is based on phase-shifted Rugate thin-film spatial filter, narrow bandpass filter and the combined device of long-wave-pass and short-wave-pass cutoff filters, and the angular spectrum bandwidth of bandpass filter are up to submillimeter radians. We mainly discuss three design methods and point out their advantages and disadvantages to find out the best one. The experimental results show that the effects of random and system error during depositing the filter is mainly responsible for the deviation of the designed and measured values.

We demonstrate a new four-core fiber optic tweezers by polishing the end face of a four-core fiber into a truncated pyramid that is asymmetric to fiber cores. Optical intensity propagation and distribution are modeled numerically, and rotation function is developed by means of calculating three-dimensional trapping force and torque in ray optics regime. Simulation results show our tweezers is a feasible approach that can trap and rotate microscopic spheroid objects stably.

Based on elasto-optic effect theory, we present a simplified model for the fiber squeezer assisted with a piezoceramic actuator (PZT), and it is experimentally demonstrated with reasonable approximation. Results show that there is a quadratic polynomial relationship between the arccosine reciprocal value of light intensity outputted from polarization analyzer and the reciprocal value of applied voltage for the PZT. Using this formula, the key parameters of the PZT such as the piezoelectric strain coefficient are further obtained. Our conclusions are significant for accurate measurement and polarization control.

We report the experimental study on mode instabilities (MI) in large mode area step-index fibers by testing a 30/400 mm step-index fiber in a single-pass co-pumped all-fiberized amplifier, delivering up to ~550 W of extracted output power without MI. The pump power is increased well above the MI threshold to study the temporal dynamics of MI in detail, which are characterized by using both high-speed camera measurement with ~2200 frames per second and photodiode traces. The experimental results are compared with the theoretical results. The MI frequency component is seen to appear on top of system noise, such as electric noise, which shows that system noise may influence the onset of MI. The beam quality of the fiber amplifier is measured, which is ~1.4 before the onset of MI, and degrades gradually to ~2.1 after the onset of MI.

Compared with the conventional diode-pumped ytterbium-doped fiber amplifiers (YDFAs), tandem-pumped YDFAs are regarded as a better solution for high power scaling. In this letter, we compare and analyze the two types of pumping scheme with respect to beam quality (BQ). The numerical model adopted by us is based on steady-state rate equations with consideration of transverse mode competition. The results show that tandem pumping is not only suitable for high power scaling but also has an advantage over direct diode pumping in BQ. For instance, the power fraction of fundamental mode in tandem pumping at 1030 nm is about 4% higher than its corresponding value in direct diode pumping at 976 nm under the condition of counter-propagating pumping configuration with the same fiber parameters except cladding diameter. Mode selection by controlling dopant distributions and coiling the fibers is also simulated and discussed. Moreover, the simulation results show that the tandem-pumped YDFAs have lower photodarkening rate than the conventional YDFAs at part area of gain fiber, but there is no obvious difference between them from the mean perspective of entire gain fiber.

It is highly necessary to study the phenomenon of photon migration in the knee joint for the non-invasive near-infrared optical early diagnosis of the osteoarthritis of the knee. We investigate the migration trace and distribution rule of the photons in knee layered structure, which are simulated by the Monte-Carlo modeling. The proportion of photons which collide with bone tissue then migrate out of the muscle tissue and photons directly migrate out of muscle tissue is calculated. For analyzing the signal-to-noise ratio to determine the accurate position of the detector, we perform quantitative evaluations of distribution of photons, as well as qualitative assessments of the distribution of photons.

We present theoretical studies on the wideband design of bulk lithium niobate (LN) acousto-optic deflector (AOD) through the walk-off design of the ultrasonic vector, which satisfies the momentum match condition. The ultrasonic properties of LN crystal are studied by solving the Christopher equation and the reciprocal velocity curves in the operating planes XOZ and YOZ are systematically obtained. The calculation results show that the bandwidth of the AOD is highly dependent on the incident angle of light beam and the velocity of the ultrasonic waves, which show strict linear properties in the operating bandwidth. Furthermore, the dependence of the central frequency of the AOD on the angle of incident light and the ultrasonic velocity are also analyzed.

As aerospace technology develops rapidly, higher demand for aerospace optic system is brought forward. With its excellent physical qualities, SiC becomes a very promising material for speculums. The material-remove mechanism of SiC surface polishing is studied, that is, the grinding mechanism of ceramic material. Indentation fracture model is also introduced and is used to explain material-remove mechanism of SiC surface polishing, and the model of SiC polishing in ideal condition is analyzed. Finally, the material-remove mechanism of SiC polishing in real state is studied.

Swing arm profilometer is a useful metrology tool for large optics. For larger mirrors, the testing accuracy decreases as the arm becomes longer, while the testing accuracy requirement remains the same. We introduce a simple solution to make testing of large mirrors with shorter arms possible, which improves the testing accuracy, especially reduces the uncertainty of low-order shapes like astigmatism and trefoil. Simulation and experiment results show that testing uncertainty of low-order shape and high-frequency errors reaches 0.1 \mu m RMS, which faithfully meets the requirement of profile testing to guide the grinding and coarse polishing process.

In order to obtain high-quality flat mirror, a serial mode combined polishing technology, consisting of continuous polishing (CP) and ion beam figuring (IBF), is presented. The function of CP technology is to get certain figure accuracy and meet the requirements of the surface roughness of the flat mirror. The final high figure accuracy of the flat mirror is achieved by the IBF technology. We introduce the polishing principles of CP and IBF and then, the polishing experiment and material removal function of IBF are studied. Finally, a F 160 mm flat mirror is polished by a serial mode combined polishing technology. After serial mode com-bined polishing, the surface error and roughness of the flat mirror are 2.06 and 0.42 nm RMS, respectively. The experiment results indicate that the serial mode combined polishing technology is effective for polishing ultra-precise flat mirror.

Off-axis aspherical mirrors are growing in popularity in modern space-borne cameras having high resolutionand large field of view. Fabrication processes for these mirrors include surface generation by grinding wheel, free-abrasive lapping, and various polishing cycles. Surface generation by grinding wheel is the most efficient process among the whole fabrication processes. Therefore, technologies for accurately and cost efficiently generating the mirror blanks are highly indispensable. We propose, a single-point grinding mode and a four-step tool path generation technology to resolve the over travel problem, for directly machining the off-axis aspherical mirror blank. Technologies for surface geometrical modeling and wheel wear reduction/compensationare established. Using a commercial-available HASS-VF8 machining center, a silicon carbide mirror blank having a 1.45 m aperture is successfully generated. Result indicates that the main error source affecting the obtained grinding accuracy is wheel wear amount, other than the positioning accuracy of machining center. Therefore, error-compensation grinding is indispensable. We provide an alternative economical resolution to efficiently fabricate the large-scale off-axis aspherical surface.

We present the mechanism of coherent population trapping (CPT) atom clock. The optical system is designed for a portable CPT atom clock. In this system, single transverse mode vertical-cavity surface-emitting laser is used as a miniature pump laser. The driven circuit is designed based on a field-programmable gate array full digital control system and special-purpose chip MAX1968. The experimental results show that the optical system can provide circularly polarized light, and has small volume and low power consumption. These indi-cate that the optical system is a promising candidate for a portable CPT atom clock engineering prototype.

Silicon (Si) modification layer on silicon carbide (SiC) surface is widely used in space optical systems. To achieve high-quality optical surface, the technology of ion beam figuring (IBF) is studied. The radio frequency ion beam source is introduced briefly. Then the removal function experiment is studied. The volume removal stability of the IBF reached 97% in 10 h continuous working testing. The parameters of the IBF removal function are calculated by Gaussian fitting including the removal rate and the full-width half-maximum. Then the removal function results are used in practical fabrication. The workpiece is a plane with Si modification layer on SiC surface. After 148 min processing IBF, the final surface error reaches 1.2 nm RMS.

Hyperspectral optimization process exemplar, a&bb-based K model, and a water column correction model are used to process the hyperspectral data for detecting the subtle spectral difference of coral reefs. The water column correction model only tracks those effective photons by fully considering the geometrical distribution of the light field. The adaptivity of the parameters and models to the in situ data collected in Sanya Bay is evaluated. The modeled and uncorrected spectra are examined separately to reflect the coral reflectance, and the coefficients of determination for the relationships drops from 0.90 to 0.05. The retrieved bottom reflectance for 70 corals (Acropora, Porites) exhibited the classic chlorophyll features. The reflectance at 700 nm collected in Sanya Bay is relatively lower than the results conducted by other researchers. Peak ratio index and derivative analysis are utilized and are proved to be effective for coral reef classification and coral healthy assessment.

In this letter, we propose a novel adaptive image enhancement algorithm based on nonsubsampled contourlet transform (NSCT) coefficient histogram matching. Firstly, the original image is decomposed in the NSCT domain. Secondly, the NSCT coefficient histograms of the original image in corresponding subbands are adaptively mapped to those of the reference image via histogram matching after threshold denoising. Finally, the enhanced image is reconstructed from the modified coefficients via inverse NSCT. Experimental results demonstrate that the proposed adaptive algorithm effectively improves subtle features while suppressing noise compared with existing algorithms.

The quantitative analysis of X-ray fluorescence (XRF) spectra is studied using the partial least-squares (PLS) method. The characteristic variables of spectra matrix of PLS are optimized by genetic algorithm. The subset of multi-component characteristic spectra matrix is established which is corresponding to their concentration. The individual fitness is calculated which combines the crossover validation parameters (prediction error square summation) and correlation coefficients (R2). The experimental result indicates that the predicated values improve using the PLS model of characteristic spectra optimization. Compared to the nonoptimized XRF spectra, the linear dependence of processed spectra averagely decreases by about 7%, root mean square error of calibration averagely increases by about 79.32, and root mean square error of cross-validation averagely increases by about 14.2.

The optical fiber nanoprobe is prepared using spark fused taper and acid corrosion methods. With 3-ami-nopropyltrimethoxysilane coupling, gold nanoparticles are solidified onto the surface of fiber optic and then the optical fiber sensor is prepared using the surface-enhanced Raman spectroscopy (SERS) measurement of the cell solution. The SERS of the esophageal cancer cell solution is measured by direct detection and fiber detection methods. Similar results are obtained by both detection methods. SERS measurement of tissues and organs is done using the optical fiber sensor.

In this paper, we present the development and application of a full-aperture backscatter diagnostics system at the Texas Petawatt Laser (TPW) facility. The diagnostic system includes three independent diagnostic stations. With this system, we obtained TPW on-shot focus properties, and high-harmonic spectral emission from solid foils (e.g., Cu and Al) and their Si substrate in an experiment to study laser hole boring, which show the hole-boring mechanism at relativistic intensities. The measured on-target full-power focal spots from ultrathin film targets help determine the optimum target thickness at certain laser contrast parameters for particle acceleration and neutron generation experiment, which is also a relative measurement of shot-toshot intensity fluctuations.

We investigate the terahertz (THz) wave emission from air plasma by analyses and simulations. An elliptically polarized THz wave is generated, whereas a circularly polarized carrier-envelope phase (CEP) stabilized few-cycle laser pulse is applied. Its ellipticity and intensity depend on the pulse duration of the driving laser pulse. And the polarization rotates along the CEP of the driving laser pulse. The THz generation is also simulated for different filament lengths. As the filament extends, the polarization of the generated THz wave rotates along the filament.

We simulate the integrated effects of atmospheric aberration, atmospheric turbulence, thermal blooming, random jitter of laser's intensity and phase, speed of wind, direction of wind, absorption of air, kinetic cooling of CO2 and N2, speed of target, output power and beam quality of laser, wavelength, focus length, and the launch altitude of laser to accurately simulate the transmission loss of the laser's energy, concentration of laser's power and other beam quality parameters of the laser propagating to the dynamic target. And we evaluate the efficiency of laser's irradiation on the target more accurately for the optical link of ground-to-airspace. We also investigate influences of characteristics of dynamic parameters (Strehl's ratio, RMS of wave-front, spatial distribution of intensity on the target, the real focus on the optical link and the peak intensity along the propagation path) including speed of wind, direction of wind, speed of target and the kinetic cooling effect of air, especially. We conclude that the higher speed of wind and target weakens the thermal blooming of atmosphere and improves the beam quality and efficiency of laser's irradiation on the target. The kinetic cooling effect of air is more remarkable to improve the beam quality irradiating on the target at the initial part of the propagation path of the laser. The changed direction of wind weakens the atmospheric aberration and directs to better beam quality and higher efficiency of laser's irradiation on the target.

An integer coordinate commutation project is advanced which leads the aim angle information form optic–electronic detecting system to aim map orientation system and then to countermine system under the middle precision GPS orientation section. This way can we solve the difficult problem that the warning aims coordinate commutation among many optic–electronic vehicle systems. The aim orientation is realized by neat matrix principle. First, the 12 coordinate systems of optic–electronic detecting vehicle system and laser countermine system are defined. Then, the aim coordinate transform mode is changed from the warning sys-tem to the countermine system. It seems that this mode can satisfy the "360" error request of the two vehicle optic–electronic system aim coordinate leading orientation under the complexion of without regarding to the relatively position and angle of the optic–electronic detecting vehicle and laser countermine vehicle.

An asymmetric large optical cavity (LOC) waveguide is designed to raise the output power of the 940 nm laser diode. By optimizing the metal organic chemical vapor deposition growth condition and combining with the electrode fabrication and facet coating, single emitter semiconductor laser diodes of 95 mm strip width and 4 mm cavity length are fabricated. Without any active cooling process, an output power of 13.4 W is reached at 15 A injection current without catastrophic optical mirror damage at room temperature. By introducing the asymmetric LOC waveguide, the far-field test shows that only the transverse fundamental mode is lased with a vertical far-field angle full width of half magnitude of 22o.