Transparent Fourier transform spectrometer

We realized a transparent Fourier transform spectrometer and investigated its operating principle. The spectrometer consists of a low-reflectivity Fabry-Perot interferometer and a partially transparent photodetector, which allows for the operation of the spectrometer in transmission. By changing the distance between the low-reflectivity mirrors of the Fabry-Perot interferometer, the light intensity that reaches the partially transparent photodetector is modulated and the spectral information of the incident light is determined by the Fourier transform of the generated photocurrent. This transparent Fourier transform spectrometer allows easy miniaturization and integration into any kind of optical system.     

Field-compensated birefringent Fourier transform spectrometer

A field-compensation method applied for Savart birefringent Fourier transform spectrometer is presented. By using a combination of Savart plates fabricated from positive and negative birefringent materials, the useful solid angle of field of view can be increased by a large amount in broad spectral coverage. Compared to the conventional Fourier transform spectrometers, the compensated field angle has optical throughput higher by one order in magnitude. To demonstrate the effectiveness, a design example operating at 400-1100 nm with a large solid angle exceeding ± 40° is presented in detail.     

Birefringent prism based Fourier transform spectrometer

This paper presents the design of a rugged and compact Fourier transform spectrometer (FTS) utilizing a birefringent prism, a pair of polarizers and a linear CCD array. This design improves on existing FTS by eliminating moving parts and spreading the optical path difference (OPD) spatially (rather than temporal scanning), making the system smaller, more reliable, and dramatically reducing measurement times. Both the theoretical models for the design and experimental results of the prototype are presented. The optical performance is tested using LEDs of known wavelengths, with the fringe counting technique employed during interferogram acquisition to ensure accurate sampling of the interferogram at constant OPD intervals. Reconstructing the spectra showed that the detected wavelengths deviated from the actual wavelengths by less than 1 nm.     

教学用自组式傅里叶变换光谱仪

对原有的傅里叶变换光谱实验进行了全面的升级改造，研制了一种新型的教学用自组式傅里叶变换光谱仪，波长精度较原有实验提高了两个数量级，由该仪器构成的傅里叶变换光谱实验内涵丰富，不但可以使学生学习一种重要的光谱技术，更可以很好地培养学生综合运用所学知识解决实际问题的能力。     

空间调制微型傅里叶变换红外光谱仪研究

针对目前环境、医疗、空间、气象、军事及安全等领域对傅里叶变换红外光谱仪微小型化、轻量化及固态化的迫切需求,提出并研究了一种以MOEMS多级微反射镜为核心器件的空间调制微型傅里叶变换红外光谱仪。在理论研究方面,建立了空间调制微型傅里叶变换红外光谱仪的物理模型,探究了该系统的光场分割与空间采样的光学原理;分析了多级微反射镜的衍射效应,提出了一种通过补边抑制衍射噪声抑制方法;进行了多级微反射镜采样误差的分析,并提出了基于最小二乘拟合的修正算法;通过对光源空间相干性、准直系统像差以及入射光场均匀性的分析,确定了光学系统的总体设计指标;通过对多级微反射镜基片加工精度、分束器材料色散特性和膜层透射效率等的计算分析,确定了干涉系统的设计方法与技术参数。在核心技术方面,提出了两个多级微反射镜的3种制作方法,分析了制作误差的来源及对系统性能的影响。通过工艺设计及实验条件探索,分别采用电铸法、真空镀膜法以及斜面倾角叠片法制作了两个多级微反射镜。在系统设计方面,进行了红外准直与缩束系统的光学设计,对整体光机系统进行了建模仿真,分析了杂散光噪声的来源。在图谱处理方面,利用过零采样方式,通过图像分割算法,获取了干涉图采样序列;通过对干涉图序列的插值、补零、延拓与卷积方法,完成了光谱相位误差的校正;通过离散傅里叶变换解调,实现了由干涉图像到信号光谱的数据反演。最后研究了系统光机整体的集成组装技术,并对原理样机进行了实验测试。本文研制的空间调制微型傅里叶变换红外光谱仪的特点在于:取消了动镜驱动机构与采样控制机构,具有微小型与轻量化的特点;干涉图的采样由多级微反射镜完成,其空间采样的方式增加了系统的稳定性与可靠性,实时采样的特点增加了系统的快速性与有效性;多级微反射镜阵列采用MOEMS工艺技术制作,增加了系统的采样精度。该光谱仪系统的结构及制作方法具有自主知识产权,并具有广阔的应用前景。     

傅里叶变换红外光谱仪干涉仪系统的设计

设计了一种基于立体角镜与固定平面镜组合的干涉仪系统,以解决传统傅里叶变换红外光谱仪中干涉仪系统由于动镜的倾斜与横移影响光谱质量的问题。系统包含一对立体角镜,两面相互垂直的固定平面镜,以及分束器。通过对立体角镜的倾斜与横移、立体角镜垂直度误差以及两固定平面镜的倾斜与垂直度误差对干涉信号初相位与调制度的影响进行分析,表明立体角镜的倾斜与横移、固定平面镜的垂直度误差等因素不会影响干涉信号的初相位与调制度;通过对干涉仪进行实际测试表明,仪器具有结构简单紧凑、密封性好、分辨率高以及抗震性强等优点。     

Fourier transform spectrometer instrument lineshape (ILS) retrieval by Fourier deconvolution

This work presents a Fourier deconvolution (FD) technique for retrieving the instrument lineshape (ILS) function of high-resolution Fourier transform infrared (FTIR) spectrometers. The ILS retrieved by FD is compared with the results obtained using the LINEFIT technique of Hase. The effect of a non-ideal ILS function on quantitative analysis of HBr is explored and improvements in the results of quantitative analyses are demonstrated.     

A Fourier transform Raman spectrometer with visible laser excitation

We present the development and performance of a Fourier transformation (FT)‐based Raman spectrometer working with visible laser (532 nm) excitation. It is generally thought that FT‐Raman spectrometers are not viable in the visible range where shot noise limits the detector performance and therein they are outperformed by grating based, dispersive ones. We show that contrary to this common belief, the recent advances of high‐performance interference filters makes the FT‐Raman design a valid alternative to dispersive Raman spectrometers for samples which do not luminesce. We critically compare the performance of our spectrometer to two dispersive ones: a home‐built single channel and a state‐of‐the‐art charge coupled device‐based instruments. We demonstrate a similar or even better sensitivity than the charge coupled device‐based dispersive spectrometer particularly when the laser power density is considered. The instrument possesses all the known advantages of the FT principle of spectral accuracy, high throughput, and economic design. We also discuss the general considerations, which helps the community reassess the utility of the different Raman spectrometer designs. Copyright © 2015 John Wiley & Sons, Ltd.     

全景环形成像傅里叶变换光谱仪光学系统设计

提出了一种可以实现红外全景环形光谱成像的新型傅里叶变换成像光谱仪结构,该成像光谱仪以共焦双曲反射镜组作为全景环形集光器,利用Schwarzchild物镜进行准直,结合弹光调制干涉仪,成像透镜组以及HgCdTe红外焦平面阵列构成。介绍了全景环形成像傅里叶变换光谱仪基本工作原理及成像特性,讨论了双曲面反射全景环形集光器和Schwarzchild物镜准直器等各光学结构的设计方法,并给出了设计结果及优化方案。最后,采用Zemax光学设计软件对系统进行了光线追迹和优化,结果表明,成像光谱仪工作在8 ｍ~12 ｍ波段,有效焦距为-0.67 mm,侧向视场为40~80,F#0.9,像点弥散斑RMS半径为20.116 m,在一个像元直径内,MTF在16 lp/mm处均高于0.5,且各视场一致性较好,OPD像差在0.4范围内,成像质量良好。     

Fourier transform ultraviolet-visible spectrometer based on a beam-folding technique

A beam-folding technique in optical interferometry, where the number of beam folds used can be very large, is reported. This technique can be used as a low-cost position-tracking method in a Fourier transform spectrometer (FTS) to cover the broad spectral range from UV to IR. The main advantage gained is the simple position-tracking algorithm used in sampling the interferogram. We have developed a UV-visible FTS, whose wavelength coverage is limited only by the optical elements (350 nm(-1) microm with off-the-shelf components). Preliminary results show that it can achieve a resolution of approximately 4 cm(-1) even with a ball-bearing translation stage.     

Miniaturized time-scanning Fourier transform spectrometer based on silicon technology

We present a miniaturized Fourier transform spectrometer (FTS) based on optical microelectromechanical system technology. The FTS is a Michelson interferometer with one scanning mirror. A new type of electrostatic comb drive actuator moves the mirror. We have measured a nonlinearity of the driving system of +/-0.5 mum for a displacement of 38.5 mum . A method is presented to correct the spectrum to get rid of the nonlinearity. The driving reproducibility is +/-25 nm. The measured resolution of the spectrometer after the phase correction is 6 nm at a wavelength of 633 nm.     

Analysis of a moderate resolution Fourier transform imaging spectrometer

A moderate resolution Fourier transform imaging spectrometer based on a modified Michelson interferometer is presented. The moving part of the interferometer is a moving wedged prism (MWP) instead of a moving mirror. The principle of the interferometer is described and the optical path difference as a function of the displacement of the MWP is calculated. Theoretical calculation and analysis are presented for the two moveable directions (hypotenuse and right angle side) of the MWP. The modified Michelson interferometer is not so sensitive to the non-uniform variation of moving speed and the environmental vibrations compared with the conventional Michelson interferometer. It is compact and has a large numerical aperture. The interferometer facilitated by CCD camera and the accompanying digital hardware and software are becoming the imaging spectrometer with moderate resolution is applicable in ultraviolet-infrared region.     

Experimental study of Fourier transform spectrometer based on MEMS micro-mirror

We propose a new Fourier transform spectrometer based on programmable microelectromechanical systems(MEMS) micro-mirror and an improved Michelson interferometer.The principle of the spectrometer is theoretically analyzed.A signal acquisition unit and an experimental set-up are designed.The spectrum of the polychromatic light source is obtained at a slantwise reflector angle of 0.238°.The spectrum is analyzed by this system within the near infrared.The experimental results show that the spectral accuracy is less than 3 nm,and the signal-to-noise ratio(SNR) is 18 dB.The spectral resolution is less than 16 nm.     

全反射式高分辨率傅里叶成像光谱仪的研究

提出了一种基于分波前干涉结构的全反射式高分辨率傅里叶变换成像光谱仪。其中前置望远系统及干涉成像系统都采用了反射式光学元件,反射表面镀金属反射膜,使系统可应用与很宽的光谱范围内。分析和讨论了光谱仪的工作原理及光学结构,设计了两种可行的光路结构图,并通过初步实验验证了系统的基本性能。     

空间采样傅里叶变换光谱仪光谱反演研究

根据相似性准则,对采集到的干涉图像进行干涉图元的拆分,通过寻址定位,得到与离散光程差序列相匹配的采样干涉图序列。采用过零采样方式,对大单边干涉图序列与小双边干涉图序列利用不同的窗函数进行切趾。为了校正相位误差,结合所研究采样干涉图的特点,对频域光谱乘积校正和空域干涉图卷积校正进行了研究和改进,获得了比较理想的光谱线形,其中空域干涉图卷积校正后的光谱偏差仅为0.012088,具有最好的校正效果。     

Molecular beam millimeter sidebands Fourier transform spectrometer (MB-MMSBFT)

The high resolution Fourier transform technique has been extensively applied in the centimeter range. In the past few years great progress have been made in observing molecular complexes. Most instruments operate between 2 and 26 GHz. So, very light interesting molecular species cannot be observed. The extension of the method towards the millimeter range suffers important technological shortcomings. A sidebands generation technic allowing the generation of very short pulses, all over the millimeter wave range, is described. For the first time, the experiment is performed in a resonant cavity and on a supersonic nozzle beam.     

摆镜扫描傅里叶变换光谱仪光程差计算

摆镜扫描傅里叶变换光谱仪利用摆动扫描方式产生光程差,减小了因动镜倾斜带来的误差影响。从摆扫干涉光谱技术原理出发,对摆镜扫描傅里叶变换光谱仪的光程差进行理论分析,给出了光程差计算表达式,实验结果表明:该光谱仪光程差近似正比于摆动角度。分析了轴外光线因不同入射角所产生的附加光程差,为傅里叶变换光谱仪的指标确定和优化设计提供了理论依据。     

Time-domain surface profile imaging via a hyperspectral Fourier transform spectrometer

We describe a method for time-domain surface profile measurements via white-light reflection spectroscopy using a hyperspectral Fourier transform spectrometer (HS-FTS). This technique measures the frequency of the spectral modulation of reflected light from a multilayer optical surface and reports the spatially resolved optical thickness. Owing to the Fourier relationship, the Fourier transform spectrometer manifests this spectral modulation as temporal satellites in interferogram space. We show that measurement of the positions of these satellites can be used to reconstruct the optical thickness profile over a surface using the HS-FTS.     

Laser and Fourier transform emission spectroscopy of TaCl

The emission spectrum of TaCl has been recorded at high resolution in the 3000-35 000 cm⁻¹ region using a Fourier transform spectrometer. The bands were observed by microwave excitation of a mixture of TaCl₅ vapor and 3.0 Torr of He. Several TaCl bands have also been recorded using the laser ablation/molecular beam source at the University of New Brunswick. A rotational analysis of a number of bands has been obtained and the majority of the stronger bands have been classified into three groups with different lower state spectroscopic constants. The three lower states have been identified as having Ω″ = 0⁺, Ω″ = 2, and (tentatively) Ω″ = 3. The Ω″ = 0⁺ and Ω″ = 2 states are very close in energy and one of these two states is the ground state of TaCl.     

A build-up cavity for Fourier transform emission experiments

We have recorded electronic spectra of some diatomic species (I₂, K₂, and NaK), to illustrate the potential power of the combination of two high resolution techniques: intra-cavity laser induced fluorescence (ICLIF) and Fourier transform (FT) spectroscopy. Active and passive optical cavities have been used, working with visible continuous wave (cw) laser sources. The active cavity is a modified commercial ring dye laser, allowing for a sample up to 25 cm in length. Dispersed fluorescence spectra recorded on a Bomem Fourier transform spectrometer showed a signal enhancement of about 10 when a molecular source was placed within the resonator. The system was tested with a heatpipe source, producing alkali metal vapour at about 300 °C. These experiments illustrate enhanced cascade excitation mechanisms in K₂; the highest vibrational levels of the electronic ground state of K₂ can be observed with surprising ease. The increase in available power within the cavity has also led to the observation of fluorescence in NaK excited by a two-photon transition (Q (66) 6¹Σ⁺ ← X¹Σ⁺ transition). Spatial limitations have driven us to build a more versatile ring cavity able to accommodate larger sources. This broad-band (590-650 nm) build-up cavity is locked by a Hänsch-Couillaud servo-loop to an input laser of (instantaneous) bandwidth ∼1 MHz. Power enhancement factors of around 30 have been obtained with a 2.6% input coupler. The performance of the build-up cavity has been tested by recording FT spectra of intra-cavity laser induced fluorescence of iodine. The technique clearly has useful applications for weakly absorbing species, or for those whose electronic states are inaccessible to single-photon absorption techniques. This paper describes the arrangement we have used, highlighting some of the advantages and describing some of the particular difficulties we have encountered.