Quasi-single-photon sources are attracting a lot of interest in many fields at present; however, the knowledge is very poor about their performance. In this Letter, by using the standard Hanbury-Brown-Twiss measurement method, we investigate in detail the characteristics of the photons from an attenuated continuous single-mode red laser. For the first time to our knowledge we obtain the coincidence counting spectrum of a commercial single-photon source, which demonstrates that an appropriately attenuated continuous laser can be utilized as a quasi-single-photon source for general applications.

The nonideal semi-Gaussian beam generated in our work has a certain ascent border width. Due to its asymmetry, the propagation properties of a nonideal semi-Gaussian laser beam in nonlinear materials have some unique characters. In our work, the propagation properties of a nonideal semi-Gaussian laser beam with a small ascent border width through a ZnSe nonlinear crystal is theoretically studied, and the relations of the propagation properties and the various parameters of the nonlinear medium and the semi-Gaussian beams are also analyzed theoretically in detail.

In our work, a high-quality broadband femtosecond optical vortex is obtained by use of a continuous spiral phase plate (SPP) to modulate an ultrashort femtosecond (fs) laser with a broadband spectrum. The experimental results demonstrate that the continuous SPP is of good quality and that it can be used to efficiently produce a high-power fs optical vortex.

A low-coherence fiber-optic dynamic light scattering (FODLS) technique is utilized to measure the effective viscosity of colloidal suspensions over a range of temperatures and volume fractions. Based on the single scattering theory, the volume fraction dependency of the effective viscosity can be obtained from the analysis of the single scattering spectra measured using FODLS. Experimental data on the viscous at Brownian short-times of colloidal suspensions are compared with theoretical results. The effective viscosity is in good agreement with the theoretical values by considering the Carnahan–Starling approximation. It is confirmed that the effective short-time viscosity of colloidal suspensions at different volume fractions and temperatures can be measured by the low-coherence FODLS technique.

A new filter spectrometer for the simultaneous measurement of plasma ion temperature and rotation velocity on the experimental advanced superconducting tokamak is proposed. The Doppler broadening and Doppler shift of the plasma spectral line is determined by the signal intensity ratio of the three-filter channels that have different peak wavelengths. A rapid calculated algorithm of the temperature and rotation velocity is presented. This filter spectrometer will allow researchers to measure spectra with a temperature and velocity range of 0.1–5 keV and 250 to 250 km/s, respectively.

Null lenses are always used to test large convex aspheric mirrors. For large convex aspheric mirrors with large deviate wavefronts from the aspheric wavefront to its best sphere wavefront, a traditional null lens composed of a flat and a sphere cannot be used to test. An aspheric null lens needs to be designed and manufactured to test a large convex aspheric mirror with a large deviate wavefront. Another traditional null lens is used to guide the manufacture of the aspheric null lens. The accuracy and feasibility of the aspheric null lens are unknown and should be tested by a high precision computer-generated hologram (CGH). In the article, we introduce the principle of a null lens, designed an aspheric null lens to test a Φ338 mm aspheric SIC mirror whose radius of curvature is 1024 mm, the deviate wavefront from the aspheric wavefront to its best fit sphere wavefront is 66.5728λ PV (λ=632.8 nm). The result of the aspheric null lens that is tested by a CGH is 0.018λ RMS and satisfies the need of accuracy. The test result of the aspheric mirror is 0.030λ RMS.

In order to solve the problem of direction discrimination and low-speed measurement for a spatial filtering velocimeter, a method of frequency shifting is put forward. The filtering device is constructed by a CMOS linear image sensor that is employed both as a differential spatiotemporal filter and as a photodetector. Frequency shifting is realized by shifting the pixels of the image sensor, and the shifting is implemented digitally. The power spectrum of the output signal is obtained by fast Fourier transform (FFT). Given the limited resolution of FFT, a frequency spectrum correction algorithm, called energy centrobaric correction, is utilized to improve the frequency resolution. The built system is used to measure the transverse velocity of a simple pendulum. The results of theory analysis and experiments verify the feasibility of direction discrimination and low-speed measurement by the method of frequency shifting. Experimental results also show that the method of energy centrobaric correction can improve the velocity resolution by more than one order of magnitude.

We set up a pulsed beam steering system with a simple feedback control method. The system applies an integration circuit to process a 2 μs short pulsed beam with a repetition rate of 25 Hz, and employs an iteration method to correct the beam with a reasonable feedback gain factor. The beam steering system achieves a performance of 30 μm position accuracy and 30 μrad pointing accuracy, and it can not only compensate the drift of the laser source but also correct the external disturbance. The design can be directly applied as a lithography tool.

Some problems and confusions related to matrix analysis for Gaussian beam reflection are clarified. We can choose right-handed coordinates before and after mirror reflection which is called the traditional coordinate system in this Letter. We can also choose a coordinate system with chirality inversion which is called a novel coordinate system in this Letter. The matrix describing optical components should coincide with the selected coordinate system; errors or confusions will appear otherwise. Spherical mirror reflection and coordinate rotation in nonplanar ring resonators are used to clarify some confusion in previous publications due to disorder of the coordinate system. This work is significant to both Gaussian beam propagation analysis and ring laser resonator design.

We report a Q-switched self-Raman third-Stokes laser at a wavelength of 1487 nm, with a YVO4/Nd:YVO4/YVO4 composite crystal and a high-power fiber-coupled diode laser array at 808 nm. The maximal average output power at 1487 nm is measured to be 506 mW, at an incident pump power of 34 W and a pulse repetition frequency (PRF) of 30 kHz. The corresponding optical conversion efficiency is 1.49%. To our knowledge, our Q-switched self-Raman third-Stokes laser at 1487 nm on a YVO4/Nd:YVO4/YVO4 composite crystal is reported for the first time.

An amplified and narrow-linewidth distributed feedback fiber laser in a master oscillator power amplifier (MOPA) configuration is presented. It consists of a distributed feedback fiber laser as the seed laser and an MOPA structure in an all-single-mode fiber system. The optimized narrow-linewidth fiber laser has an over 15% efficient slope. The packaged laser module shows excellent performance including a narrow linewidth of 2 kHz, low relative intensity noise below 100 dB/Hz at the relaxation oscillation frequency, and low phase noise, which make it very suitable for interference and distributed sensing applications.

For polarization switching (PS) and nonlinear dynamic behaviors (NDBs) of an optically injected laser system composed of a master vertical-cavity surface-emitting laser (VCSEL) and a slave VCSEL, we put forward a novel manipulation scheme by means of electro-optic (EO) modulation with quasi-phase matched technology. It is found that the PS of the slave VCSEL subject to parallel or orthogonal optical injection takes on a change of periodic oscillation with the applied transverse electric field. The optically injected slave VCSEL can experience different NDBs evolutions when the light from the master laser is modulated by the linear EO effect.

We investigate propagation of a finite energy Airy beam in a gradient-index fiber analytically and numerically, and find that the beam not only repeats its intensity features, but also has the phenomenon of self-focusing and self-accelerating periodically. The numerical results show that the beam centroid position and beam width evolve periodically. The radial gradient of the refractive index determines the propagation period for the beam and the truncated parameter affects the amplitude of both the centroid position and beam width.

A Collins formula method with a scaling factor between the target and source plane is proposed for laser propagation in optical system design, which can be used to evaluate laser optical system performance and tolerance analysis. The laser propagation in optical systems can be calculated by the Collins integral formula, and an angular spectrum method is derived by coordinate substitution. It is introduced a scaling factor m, making the choice of the observation plane more flexible and the calculation more accurate. A laser optical system is designed, and its tolerance analysis is conducted by the angular spectrum method. The evaluation criterion is the laser spot radius in the far-field, which is defined by 86.5% power in bucket. The radius of the laser spot in 90 m distance is from 0.8 to 1.4 mm by the tolerance analysis, which the ideal expectation is 0.92 mm and the experimental result is 1.01 mm. In the distance of 47 m, the radius is from 0.42 to 0.73 mm by the tolerance analysis, which the ideal expectation is 0.48 mm and the experimental result is 0.46 mm. The experimental results agree with the results of the tolerance analysis well. The focal shift for laser propagation in optical systems is validated. The experimental results confirm the calculation and they prove the use of the method in laser focus optical system design.

A new shorter T-shaped thermo-stable telescopic resonator is demonstrated in this Letter. By means of thick lens model, a longer 1064-nm telescope linear cavity is designed and simulated first by analyzing the influence of the distance between every two optical elements on the fundamental mode radius on the end mirror and the system stable zone. On the basis of the parameters analyzed, a shorter telescopic composite laser system is presented for both the 1064 and 1319 nm operating lasers that will be applicable to high-quality yellow laser generation by means of sum-frequency technology.

To obtain a laser output with a high-quality beam and a square, super-Gaussian, flat-top distribution, a high-energy laser needs to conduct spatial reshaping of the geometric outline of an injected Gaussian laser pulse and the non-uniform gain of multi-level energy amplification units. A digital micro-mirror device is very suitable for a working environment that has a high electromagnetic interference in a high-energy laser system. We present an algorithm and an experiment of spatial beam shaping that is based on the use of a digital micro-mirror device. Through secondary shaping, the near-field modulation degree of the beam (the ratio of the maximum value of the light intensity to the average value) decreases from 1.79∶1 (after primary shaping) to 1.24∶1, an improvement of 30.7%. The energy loss is 32.9%. Meanwhile, the beam after secondary shaping possesses extremely strong stability. Under the condition where the input-shaping aperture remains unchanged, the dispersity of the near-field modulation degree of the output beam is only 1.6%. Thus, the influences of the environmental changes and the random distribution of the “noise” in the beam intensity distribution are reduced.

We report on the frequency stabilization of Er-doped fiber lasers against rotovibrational absorption lines of molecular H13C14N at 1550 nm by means of the frequency modulation spectroscopy technique. The laser frequency is locked to the saturated dispersion signal of an HCN cell and reached a stability of 0.4×10 11 for a 100 s integration time without frequency modulation.

We propose a novel pulse amplification model to obtain the effective thermal equilibrium time (τETE) for Yb:YAG crystal, where τETE has impacts on the gain recovery and energy extraction. A test amplifier is set up to measure the input fluence, output fluence, and pulse duration. By fitting the numerical values to the experimental data, the effective thermal equilibrium of Yb:YAG crystal at room temperature is found to be between 60 and 120 ps. To our best knowledge, this is the first time that an exact range of effective thermal equilibrium time for Yb:YAG is reported.

The temporal evolution of Nd:YAG laser-produced Sn plasma in atmospheric pressures from 5 to 104 Pa is investigated. The results show that the extreme ultraviolet radiation exists only at the beginning of the expansion process for 20 ns. The maximum temperature of 18.7 eV and density of 9.6×1017 cm 3 are measured at 73 ns. The effects of air pressure and laser energy on the process of plasma expansion are investigated. The results indicate that the air pressure has an inhibitory effect on kinetic energy, while the electron density and temperature increase with air pressure.

We theoretically investigate the dynamics of thermalization in Au-Ti double-layered film irradiated by a femtosecond laser pulse. A nonequilibrium thermal relaxation model is proposed to study the energy deposition and transport processes during femtosecond laser pulse heating of double-layered film. The maximum phonon temperature on the Au layer can be greatly adjusted by optimizing the thickness of the Au layer. In addition, the effect of Au-layer thickness on the thermalization dynamics of the Au-Ti system is examined in detail. This study provides a new way to increase the resistance of mirrors to thermal damage in applications of high-power lasers.

We report on a spectral beam combination of five narrow-linewidth fiber amplifiers. The five-channel output beams are combined in both the near and far field using a polarization-independent diffraction grating that mainly preserves the beam quality of the individual amplifiers. Each amplifier contains a two-stage preamplifier and a main amplifier delivering about 240 W of optical power, which allows a total combined output power of 1.23 kW with an efficiency of over 95%.

In this Letter, microwave generation based on frequency multiplication with fiber ring loop modulation and microwave photonic filters is proposed and experimentally demonstrated. High-order microwave harmonics can be generated and enhanced by the fiber ring loop modulation formed by incorporating a Mach–Zehnder modulator (MZM) into a fiber ring structure. Cascaded fiber ring based microwave photonic filters (FRMPFs) are adopted to filter out the desirable harmonics. In our work, with a driving signal of 2.835 GHz, the fourth-order harmonic with a frequency of 11.34 GHz is generated by using two cascaded FRMPFs.

We demonstrate a multiwavelength Tm-doped fiber laser employing polarization-maintaining undoped fiber (PMF) based on nonlinear polarization rotation. The PMF and a polarization-sensitive isolator between two polarization controllers are used to induce the intensity-dependent loss and frequency-dependent loss to alleviate mode competition caused by homogeneous gain broadening in an active fiber. An up to four wavelengths laser operating in a cavity is observed without the PMF. After the PMF is inserted into the cavity, stable dual-wavelength operation is achieved. The output had an average power distribution. The spectral fluctuation at each wavelength is smaller than 0.9 dB.

For a long communication distance, the divergence angle of laser transmission by a space laser communication system must be sufficiently narrow to solve the energy problem. However, it needs to be magnified during the ground test before the satellite launches. This way, the two communication terminals can be constantly in the coverage of each other’s laser beam even when the tracking accuracy decreases because of the atmosphere. This Letter presents methods to magnify the divergence angle for laser transmission. The diffraction intensity distributions with different methods and their influence on communication are discussed. We provide the optimal scheme in the ground test of a certain space laser communication. The result represents the accumulated experience for the space laser communication ground test.

A new distributed temperature sensor based on stimulate Brillouin scattering (SBS) is designed by filling alcohol in a photonic crystal fiber (PCF). Since the refractive index of alcohol varies with temperature, which results in the effective mode area of the PCF varying with temperature, the output power of a pulse in fiber varies with temperature. In order to achieve a precision of 1°C for the new design, the dynamic range of power measurement equipment is only 42 dB, which is far less than the dynamic range of the frequency measurement equipment of the traditional measurement system. Some influence factors in the new system are analyzed.

In this Letter, we propose a scheme that integrates a diversity-combining technique with asymmetrical clipping optical orthogonal frequency-division multiplexing (ACO-OFDM) based on a discreet Hartley transform (DHT). Simulations are demonstrated for the DHT-based ACO-OFDM system with a diversity-combining technique. The simulation results indicate that when the optimal weighting factor is chosen, the bit error rate (BER) performance is improved by about 2 dB when the binary phase-shift keying (BPSK) is modulated and about 3 dB when the 16 pulse-amplitude modulation is modulated. Additionally, experiments are presented to verify the feasibility of diversity-combining DHT-based ACO-OFDM. In the transmission experiments, a BPSK-modulated DHT-based ACO-OFDM with a diversity-combining receiver is realized, which improves the BER performance by 1.5 and 1.3 dB for a span length of back-to-back and a 50 km standard single-mode fiber, respectively.

We present a phase difference range system with about 1.5 GHz of modulation frequencies. To reduce the phase difference drift, the high-frequency signals are synthesized by digital fractional phase-locked loops, and a differential measurement method is employed by introducing an optical switch. In order to eliminate the electrical crosstalk, a photoelectric modulator working as a mixer is used. The experimental results show that the distance error of the proposed system is within ±0.04 mm and the phase difference error is less than 0.15°.

The goal of this work is to evaluate the compositional and morphological changes of human dentin after erbium, chromium:yttrium–scandium–gallium–garnet (Er,Cr:YSGG) laser irradiation by Raman spectroscopy. The dentin surface of human molars are irradiated with an Er,Cr:YSGG laser at the output power of 3 and 3.5 W. Raman spectra before and after treatments are measured and analyzed. The results show that Raman spectroscopy can efficiently monitor the compositional changes of human dentin induced by an Er,Cr:YSGG laser. Although no new bands, band shifts, or disappearance of bands occurred, the intensities of the organic peaks associated with Amide I and CH2 are reduced significantly.

We investigate the one/two-photon fluorescence of two synthesized phenoxy-phthalocyanines (Pc1 and Pc2) using the mild reaction coordination method and the nonlinear optical properties of Pc1 and Pc2 in solution are investigated using the Z-scan technique at 800 with a 100 fs pulse width. The results show that both phthalocyanines indicate strong three-photon absorption, and the critical intensity value of Pc2 is higher than that of Pc1 when the contribution of the high excited-state absorption is introduced in the sample. Furthermore, the redshift of one- and two-photon fluorescence spectra can be explained by the reabsorption effect of the molecules. With good solubility and excellent nonlinear optical properties, the samples are expected to be a potential candidate for optical applications and photodynamic therapy.

To investigate the relationship between indium content and optical properties during epitaxial growth of an InGaAs/GaAs single quantum well (SQW), simulation and experiments are demonstrated. The epitaxial growth is demonstrated with low-pressure metal–organic chemical vapor deposition. Photoluminescence (PL) spectroscopy is applied to research the PL properties at room temperature. The In/(In+Ga) varies from 0.24 to 0.36, resulting in an increasing of the full-width half-maximum (FWHM) with the wavelength exhibiting a red-shift. A SQW with an In/(In+Ga) of 0.36 is manufactured, where a FWHM of 23.9 meV is obtained. An InGaAs SQW sandwiched by GaAsP is prepared, which is observed to exhibit a diminished FWHM of 17.0 meV with the wavelength revealing a blue-shift.

We investigate the 120 keV hydrogen ion-implanted LiTaO3 samples. To observe the implantation-induced crystal structure and composition changes we use Raman scattering, infrared spectroscopy, and cross-section transmission electron microscopy. In addition, elastic recoil detection analysis is used to detect the hydrogen concentration. Experimental results show that hydrogen ions mainly participate in the formation of platelets and micro-cracks, and diffuse out during the thermal process. Only a small portion of hydrogen is attached to the Li site and Li vacancy to form O-H. The content decrease of Li after hydrogen implantation was discussed.

The defect evolution is investigated for high-reflective coatings under multiple irradiations with an improved statistical model. The fatigue effect is observed with an increase in the shot numbers, but the fatigue process will not endure and it tends to be saturated when the number of shots reaches a certain level. With the addition of a bilayer unit, the defect density distribution of the high-reflective coatings is obtained. Two defect types are identified, and the differentiation of the high-damage precursors can well explain the decrease of the laser-induced damage threshold, as well as the saturation effect.

Second-harmonic generation (SHG) from aperiodic optical superlattices in the regime of pump depletion is investigated, when the influence of typical fabrication errors, which can be introduced by the random fluctuation of the thickness for each domain in the simulation, is considered in accordance with the actual case. It is found that both the SHG conversion efficiencies calculated in the undepleted pump approximation (UPA) and an exact solution decrease when the fluctuation increases; however, the decreasing degree is related to the wavelength of the fundamental wave (FW), and the longer the FW wavelength, the less the decrease in the corresponding conversion efficiency. A relative tolerance with respect to SHG conversion efficiency calculated in the UPA and exact solution is defined as previously [Opt. Express21, 17592 (2013)], in which a typical model based on the relative tolerance curves was proposed to estimate the SHG conversion efficiency. The simulation results show that the relative tolerance curves are basically coincident with the standard curve when the random fluctuation is very small (typically below 1%); however, as the fluctuation increases, the relative tolerance curves exhibit a large deviation from the standard curve, and the deviation is also determined by the wavelength of the FW.

The theoretical study of the film thickness distribution deposited on a parabolic substrate by vacuum evaporation is reported. It is derived that the value of n/h and L/h strongly affect the coating thickness distribution (where h is the height of the substrate and n and L are, respectively, the horizontal distance and vertical height between the evaporation source and the center of the parabolic bottom). All of the parabolic substrate can be coated when n≤ph(1+L/h) (where the parabolic focal length is p/4), otherwise there is “blind area” on the substrate. In addition, the excellent thickness uniformity of the coating on the whole parabolic substrate can be obtained by choosing the appropriate configuration of the evaporation system under different evaporation sources.

The slope of the root-mean square (RMS) can be applied to evaluate mid-spatial frequency mirror surface errors for larger-aperture mirrors. In this paper, the slope RMS is analyzed from three different perspectives. First, the relationship between the slope RMS and the basis polynomials is discussed, and the mathematical relationship between the slope RMS and the standard orthogonal basis is obtained. Second, the slope RMS is analyzed by applying the Wiener process, with the results indicating that the ideal mirror surface error obeys the Gauss distribution law. Then, a power spectrum analysis method based on the slope RMS is proposed. Finally, the method is used to analyze the Thirty Meter Telescope tertiary mirror surface figure.

This Letter reports a series of experiments on examining the removal function of a 400 mm magnetorheological finishing (MRF) polishing wheel which is aimed at large optical component fabrication. This MRF equipment is assembled on the large computer numerical control center whose effective axial length is 3000 mm. The two different removal functions of the wheel are used to virtually fabricate a 1450 mm concave fused silica aspherical optical mirror. The total fabrication times are 110 and 309 h, respectively. The final surface errors are eventually reduced to 0.014λ and 0.024λ after the process, and the convergence rates are 97.46% and 95.65% in one virtual fabrication cycle. The power spectrum density is used to analyze the spacial frequency based on the final simulating surface error, and the middle and low spacial frequency surface error controlling ability is analyzed in terms of different removal functions.

A new method developed for wavefront error (WFE) testing of an assembled space telescope is described in this Letter. The main idea of this method is to image a small bright target on the focal plane array assembly by the space telescope itself; the imaging light beams can be reflected to the focal plane array by a plane mirror in front of the aperture of the system under test and two images (one is in-focus and the other is defocused) can be obtained. The WFE of the optical system can be calculated with a phase diversity algorithm according to two images of the target on the focal plane array assembly. The residual error and limitations of this method are discussed and a simulation result is shown, which shows the application potential of this technology.

We use inductively coupled plasma chemical etching technology (PCET) operating at atmospheric pressure to fabricate an optical mirror whose materials are fused silica, reaction bonded SiC, sintered SiC, and Si for the first time, to our best knowledge. This Letter is focused on a primary study of the mirror surface roughness fabricated with a plasma torch on different wafers. The four wafers’ surface roughness after PCET fabrication are Ra 0.053, 0.223, 0.612, and 0.027 μm, respectively (increased 5, 40, 1.07, and 2 times, respectively). The micro-transformation principle of the surface roughness is researched with an Olympus LEXT 450. We analyze the main reasons that underpin the surface roughness increase. The experimental results show that the new technology is valid for fabricating Si-based materials. Consequently, inductively coupled PCET operating at atmospheric pressure shows promise for the future.

In this Letter, we present a method to measure the eccentricity of an off-axis asphere using a laser tracker during optical null testing. We first adjust the optical path of the null testing, and then probe some necessary reference surface on the compensator or the off-axis mirror’s body with a laser tracker. Next, using the collected data to process, construct, build the coordinate system, solve, and so on, we obtain the eccentricity directly through comparing the central point of the asphere and the tested optical axis. A measurement experiment is conducted with a circular off-axis aspherical mirror; the result shows that the measurement accuracy can reach 0.1859 mm, 6.2% of its tolerance belt.

Off-axis systems built by freeform optics are greatly demanded in next-generation space telescopes/cameras, for obtaining a long focal length and wide field of view. The profile accuracy of the mirror surface is the most critical parameter, which is finally required about 12 nm in peak-to-valley. Therefore, technologies for accurately and efficiently machining and testing freeform surfaces are greatly demanded. In this work, an ultrasonic-vibration-assisted five-axis grinding technology is developed and verified by grinding silicon carbide mirror blanks on a machine center having common precision. Subsequently, a computer-controlled optical surfacing technology is developed for lapping and polishing the mirror. A computer-generated hologram is developed for testing the mirror surface. This work provides an efficient resolution for the fabrication and measurement of freeform surfaces.

A derivative method for phase retrieval in two-step phase-shifting interferometry (PSI) with a blind phase shift is proposed in this Letter. By numerically calculating the first-order and second-order derivatives of two PSI images, one can directly determine the phase shift and then obtain the quantitative phase image. We illustrate the method with both a theoretical analysis and some simulations of an average-sized red blood cell in different interferometry recording modes. From the results, the validity, accuracy, as well as efficiency of this method are verified. Moreover, this method can be applied to any quantitative phase imaging, including on-axis, off-axis, and slight off-axis interferometry.

Definitions of mode-field half-width and divergence half-angle according to different kinds of methods are analyzed in this work. Numerical results of these definitions are given for the fundamental mode and suggest that some of them are more suitable for describing the transmission characteristics of a slab waveguide.

The advantages of manufacturing a space aspheric mirror of SiC material are analyzed, and the key methods and technology of fabricating and measuring SiC aspheric surfaces are introduced and researched. The off-axis SiC aspheric mirror is ground and polished by computer controlled optical surfacing (CCOS) technology with a FSGJ-2 numerical control machine, the contour and optical parameters are measured and controlled by a coordinate measuring machine (CMM) and laser tracker. Finally, an example for fabricating and testing an off-axis parabolic mirror with an aperture of 820 mm is given. A null lens is specifically designed and customized in order to test the large aspheric mirror by interferometry and null compensation. The resulting PV and RMS of the surface error are 0.335λ and 0.018λ (λ is 632.8 nm), respectively, which meets the requirements of the optical design.

We describe the design and capabilities of the x-ray excited optical luminescence (XEOL) technique at the scanning transmission x-ray microscopy beamline (BL08U1A) of the Shanghai Synchrotron Radiation Facility. The detection system is a functional expanding of the original end station, making full use of its precision positioning stages. The simultaneous collection of XEOL and total electron yield spectra is realized using homemade software when the excitation energy is scanned. The setup is validated by the 2D near-edge x-ray absorption spectroscopy (NEXAFS) XEOL mapping across the O K-edge of a nanostructured ZnO sample. The ability to detect the signal of very weak light-emitting material is verified by using TiO2 nanopowder.