Self-mode-locking of the Nd3+:KGd(WO4)2 laser using a multifunctional semiconductor mirror

A multifunctional semiconductor mirror that contains a saturable absorber based on quantum wells, a broadband reflector, and a Gires-Tournois interferometer that serves as a GVD compensator is designed and created. The mirror is fully characterized using the pump-probe technique with a subpicosecond resolution and the transmission and photoluminescence spectroscopy. The mirror that simultaneously executes the three functions and that is created in a single technological cycle provides stable mode-locking in the Nd³⁺:KGd(WO₄)₂ laser.     

Low-cost set-up for Fourier-transform infrared spectroscopy in diamond anvil cell from 4000 to 400 cm−1

An experimental set-up for Fourier-transform infrared (FTIR) studies at high pressure in the mid-IR region (400–4000 cm^?1) is constructed using a compact TEO-400 FTIR interferometer module and an external microscopic optical bench with cassegrain focusing objectives. Cassegrain-type reflective objectives act as an excellent beam condenser that facilitates the interfacing between FTIR spectrometer and diamond anvil cell. This set-up is capable of recording transmission and reflection infrared spectra at high pressure. Preliminary results are reported both in the reflection (pressure dependence of polar phonons in CuWO₄) and transmission configuration (polarized light absorption of polar phonons across the wurtzite-to-rocksalt transition in ZnO).     

自参考干涉波前传感器中针孔直径对闭环自适应光学系统校正精度的影响

使用自参考干涉波前传感器(SRIWFS)进行波前的绝对测量时,为了获得近似平面波前的参考波,针孔直径应该不大于无畸变光学系统艾里斑直径(d_A)的一半,然而这必将导致光能利用率的严重下降.为了最大程度地提高光能利用率并改善干涉条纹的对比度,研究了SRIWFS应用于闭环校正中时所允许的最大针孔直径,这将在闭环开始阶段尤为重要.数值模拟和实验表明,直径不大于1.5d_A的针孔可以获得满意的校正结果,校正后远场斯特列尔比高于80％;同时光能 关键词： 自适应光学 自参考干涉波前传感器 针孔直径 闭环校正     

Fibre-optic interferometer formed by a section of small-core fibre spliced between standard fibres

A fibre-optic interferometer based on interaction between core and cladding modes that are coupled at splices of fibres having unmatched core mode profiles is demonstrated. The interferometer is formed by splicing a section of small-core fibre that is single-mode at 630 nm between two standard fibres. The transmission spectra of the fibre interferometer are measured for different lengths of the inserted fibre section. The spectra reveal interference fringes having envelopes with two broad dips, whose positions and widths are independent of the interferometer length.     

Tunable filter based on a pair of special long-period fiber gratings and its application in fiber ring laser

A filter based on a Mach-Zehnder interferometer (MZI) formed by cascading a pair of longperiod fiber gratings (LPFGs) written by CO₂ laser in a twisted single-mode fiber is proposed. The transmission spectrum of the filter is tuned by modifying the bending curvature of the MZI, and thus wavelength tuning is achieved. And a tunable erbium-doped fiber (EDF) ring laser employing the filter as a wavelengthselection component is experimentally demonstrated. The laser can be tuned continuously from 1573.05 to 1595.75 nm with a side-mode suppression ration of ∼50 dB over the total tuning range.     

System for measuring optical admittance of a thin film stack

A new method based on the polarization interferometer structure has been applied to measure the optical admittance, the refractive index and thickness of a thin film. The structure is a vibration insensitive optical system. There is one Twyman-Green interferometer part to induce a phase difference and one Fizeau interferometer part to induce the interference in the system. The intensities coming from four different polarizers were measured at the same time to prevent mechanical vibration influence. Using the polarization interferometer, the optical admittance, the refractive index and thickness of a single layer of Ta₂O₅ thin film has been measured. The measurement results were compared with the results obtained by ellipsometer. The results meet reasonable values in both refractive index and thickness.     

Femtosecond phase spectroscopy of multi-level systems: Phthalocyanines

A femtosecond frequency-domain interferometer is applied to metal-free and vanadyl phthalocyanine (H₂Pc and VOPc) thin films to measure time-resolved difference phase and transmission spectra simultaneously. For both samples, the phase-change dynamics is different from the transmission-change dynamics at 620 nm, reflecting that the phthalocyanines (Pc) cannot be modeled with a two-level system but by a multi-level or inhomogeneously broadened system, in which each level pair exhibits different relaxation dynamics. Because of this dynamical difference, a phase-change measurement is required to correct distortion of the transient spectra due to induced phase modulation of probe pulses. Near zero time delay, the phase and transmission changes show different growth behavior. This behavior is explained by antisymmetric amplitude and phase gratings which are produced by coherent coupling between frequency-chirped pump and probe pulses. Formerly V. S. Williams     

Influence of apodization functions on continuous very far infrared spectra

We show that the continuous transmission spectrum and continuous absorption coefficient in the VFIR region (K < 50 cm⁻¹) are distorted by all the weighting functions employed in the process of apodization, when using a Michelson interferometer. We observed that the most common triangular weighting function distorts considerably the FIR spectrum. We found that the weighting function [1- (Δ²/Δ²_max)] is more appropriate for smoothing the spectrum.     

Collimation testing of a CO2 laser beam with a shearing interferometer

A shearing interferometer based on a Michelson interferometer is proposed for collimation testing of a CO₂ laser beam. The shear and tilt between the interfering wavefronts is obtained by replacing one or both mirrors of the Michelson interferometer with double mirrors arranged to act as 90 ° or near 90 ° prisms in retroreflecting mode. Detailed analysis for two experimental configurations of this system are presented.     

“Noninverted” interference fringes upon light reflection from a Fabry-Perot interferometer with an asymmetric diffraction mirror

This paper describes the calculation, fabrication, and experimental investigation of a reflection two-mirror interferometer whose front mirror is asymmetric in reflection and made as a thin-layer diffraction metal structure (Al, Ag) in combination with a dielectric coating (MgF₂, ZnS). In reflection, this interferometer creates in the zero diffraction order a transmission-like pattern similar to that produced by an ordinary Fabry-Perot interferometer operating in transmitted light.     

Simultaneous measurement of partial pressure of O₂ and CO₂ with a hybrid interferometer

In this Letter, a hybrid interferometer for simultaneous measurement of the partial pressures of O₂ and CO₂ mixtures is reported. The sensing head consists in the combination of two interferometric structures, one a Fabry-Pérrot cavity and the other a modal interferometer. The intrinsic Fabry-Pérot was formed by splicing a single mode fiber with a graded index fiber length that was then subjected to chemical etching creating an air cavity. The second interferometer is based on a splice of a pure silica tube in series with the Fabry-Pérot. It was observed for a particular gas that its refractive index changes with pressure variation in a specific way, a characteristic that permitted the simultaneous measurement of partial pressures of CO₂ and O₂ with rms deviations of ～±48.7 kPa and ～±20.1 kPa, respectively.     

Polarisation-insensitive strip-loaded waveguide for electro-optic modulators and switches

A polarisation-insensitive electro-optic (EO) waveguide consisting of a dye-doped TiO₂/SiO₂ slab and a SU-8 strip-loaded rib is designed and fabricated. By optimizing the refractive index and size of waveguide, a trade-off between polarisation-insensitive condition and large EO efficiency (optical field interaction with the EO material) is obtained. The average transmission loss of the waveguide is less than 2.0 dB/cm. A Mach-Zehnder (M-Z) interferometer intensity modulator based on this waveguide with excellent poling stability is fabricated and measured, exhibiting 7 V half-wave voltage with 1.8 cm EO interaction length and 2.7 cm total length. This strip-loaded structure is proved to be a valuable application in EO modulators and switches.     

Fabry-Perot干涉仪用于托卡马克等离子体氢氘比测量

本文在国内首次将Fabry-perot干涉仪用于托卡马克等离子体诊断。实验采用一台压电驱动式Fabry-perot干涉仪通过对H_α和D_α谱线轮廓的测量来推算等离子体的氢氘含量比,从而避免了在传统的氢氘比测量中因重复放电所引起的不准确性。     

F-P干涉仪腔镜的不平行度对高斯光束透射特性的影响

基于多光束干涉原理,推导出了高斯光束经过两腔镜不严格平行的F P干涉仪后透射光强度的表达式。在此基础上,数值研究了F P干涉仪腔镜的不平行度对高斯光束透射特性的影响。结果表明:随着F P两腔镜不平行度的增大,透射光的峰值强度总体呈现下降的趋势,且在下降的过程中会出现波动;峰值强度位置将发生移动;光斑的均方根宽度将发生变化。     

Hysteresis and nonlinear thermooptic waves in a semiconductor Fabry-Perot interferometer

We propose and demonstrate the existence of temperature hysteresis phenomena in a Fabry-Perot interferometer, resulting from a change in the refractive index of the interferometer material when heated by laser radiation. We also demonstrated theoretically that temperature multistability in the distributed interferometric system may cause the emergence of nonlinear thermooptic switching waves and found an approximate expression for the propagation velocity of such waves. We present the results of experimental observations of temperature multistability and thermooptic switching waves in a germanium Fabry-Perot interferometer illuminated by CO₂-laser radiation.     

马赫-曾德尔干涉仪消光比和单通道光开关

对马赫-曾德尔(M—Z)干涉仪的滤光消光比特性进行了研究，提出了一种在其一端加上光纤全反镜的方法，大大改善了马赫一曾德尔干涉仪的输出谱特性，由此提出并设计了一种单通道光开关，实验得到了约37．4dB的开关动态范围。     

CO2-laser with vibration-proof Q-switch

A CO₂-laser with vibration-proof Q-switching is described. Modulation is achieved by spinning a plane-parallel Ge or Si plate as Fabry-Perot interferometer. A 1.4 mm thick Si interferometer makes it possible to obtain pulses with duration of about 100 ns and a power of 50 kW, which is higher than cw generation by a factor of 2000.     

An X-ray interferometer with Bragg case beam splitting and beam recombination

A new type of X-ray interferometer which uses Bragg case transmission for beam splitting and for beam recombination is described. The principles and special problems of this interferometer are discussed and a strict plane-wave treatment of the interference phenomena is presented. The feasibility of such a device is demonstrated by some interference patterns, obtained with an instrument made from a silicon crystal for use with copperKα radiation and the 220 Bragg reflection. Since, for the operation of the Bragg case interferometer, strong absorption is not essential, such devices may also be more suitable than the previously reported Laue case interferometer^1,2 for use with neutrons.     

Quantum transport in coupled resonators enclosed synthetic magnetic flux

Quantum transport properties are instrumental to understanding quantum coherent transport processes. Potential applications of quantum transport are widespread, in areas ranging from quantum information science to quantum engineering, and not restricted to quantum state transfer, control and manipulation. Here, we study light transport in a ring array of coupled resonators enclosed synthetic magnetic flux. The ring configuration, with an arbitrary number of resonators embedded, forms a two-arm Aharonov–Bohm interferometer. The influence of magnetic flux on light transport is investigated. Tuning the magnetic flux can lead to resonant transmission, while half-integer magnetic flux quantum leads to completely destructive interference and transmission zeros in an interferometer with two equal arms.     

BER analysis on optical direct-detection FSK transmission systems using a Mach-Zehnder interferometer as a discriminator

This paper presents a BER analysis for two types of optical FSK transmission systems using a Mach-Zehnder interferometer as a discriminator. In one case the discriminator is assumed to be kept on the transmitter side and in the second case, on the receiver side. The analysis takes into account the linewidth of the source and other noises in the system. The discriminator disperses the input pulse, and an optimum filter required to produce a raised cosine output pulse spectrum is proposed. Such an optimum filter gives the minimum noise bandwidth without causing any ISI at the decision instant. The values of the equivalent noise-bandwidth factorsI ₂ andI ₃ of the filter vary between 0.563 to 0.822 and 0.086 to 0.193, respectively, when the interferometer delay time is varied from zero to bit time. BER curves are given for various conditions of the FSK systems. To avoid an error floor the linewidth of the source should be <0.01/.