Development of a laser-based fluorescence microscope with subnanosecond time resolution

This report describes the development of a fluorescence microscope based on a standard inverted optical microscope which incorporates a pulsed picosecond dye laser excitation source and a detector consisting of a gated image intensifier coupled to a CCD camera. Fluorescence images have been obtained using gate durations of 0.5 ns from this apparatus, representing a reduction in gate duration of an order of magnitude compared with similar instruments reported by others recently. Subnanosecond gated fluorescence images of V79-4 Chinese hamster lung fibroblasts stained with a phthalocyanine photosensitizer used in photodynamic therapy are presented. The results of these measurements are discussed in terms of the intracellular distribution of the sensitizer. Other potential applications and limitations of this technique are also outlined.     

浅层地下物体的高分辨声波探测

本文对地下物体的声波探测进行了初步研究，分析了探测分辨率与声波频率的关系，得出了黄土介质中声波探测的分辨极限，通过对实际目标的探测表明，该方法具有一定的实用性。     

Trace gas monitoring with infrared laser-based detection schemes

The success of laser-based trace gas sensing techniques crucially depends on the availability and performance of tunable laser sources combined with appropriate detection schemes. Besides near-infrared diode lasers, continuously tunable midinfrared quantum cascade lasers and nonlinear optical laser sources are preferentially employed today. Detection schemes are based on sensitive absorption measurements and comprise direct absorption in multi-pass cells as well as photoacoustic and cavity ringdown techniques in various configurations. We illustrate the performance of several systems implemented in our laboratory. These include time-resolved multicomponent traffic emission measurements with a mobile CO₂-laser photoacoustic system, a diode-laser based cavity ringdown device for measurements of impurities in industrial process control, isotope ratio measurements with a difference frequency (DFG) laser source combined with balanced path length detection, detection of methylamines for breath analysis with both a near-IR diode laser and a DFG source, and finally, acetone measurements with a heatable multipass cell intended for vapor phase studies on doping agents in urine samples. PACS 33.20.Ea; 42.62.Fi; 42.72.Ai; 87.64.km; 92.60.Sz     

基于中红外分布反馈量子级联激光器的光声光谱技术用于痕量甲烷气体检测

由于工业监控和环境检测的需要,甲烷气体检测日益得到人们的关注。研究了基于中红外分布反馈量子级联激光器(DFB-QCL)的光声光谱技术,并应用于痕量甲烷的检测。自主研发的DFB-QCL室温工作时的激射波长在7.6μm附近,覆盖了甲烷的特征吸收谱线1 316.83cm-1。待测甲烷气体充入亥姆霍兹光声谐振腔中,DFB-QCL的工作频率为234Hz、室温脉冲工作时峰值功率为80mW。中红外光经过甲烷吸收后,产生的声波信号经麦克风检测,由锁相放大器对信号进行采集并输入计算机进行处理。按信噪比为1计算,得到甲烷的探测极限为189nmol.mol-1。     

Diode laser-based detection of combustor instabilities with application to a scramjet engine

Fluctuations in temperature non-uniformity along the line-of-sight of a diode laser absorption sensor in a model scramjet are found to precede backpressure-induced unstart (expulsion of the isolator shock train). A novel detection strategy combining Fourier analysis of temperature time series to determine low-frequency heat release fluctuations with simultaneous measurements of multiple absorption features of H₂O to identify temperature non-uniformities was applied to the scramjet combustor. Time-resolved absorption is measured using wavelength modulation spectroscopy for three transitions chosen with different temperature-dependent absorption characteristics. The line-of-sight (LOS)-averaged temperature inferred from the ratio of absorption from one pair of transitions is highly sensitive to low-temperature non-uniformities along the absorption path while the other ratio is less sensitive. The fraction of fluctuations in the range 1 < f < 50 Hz is determined from short-time Fourier transforms (STFTs) of the measured temperatures from both transition pairs. The ratio of these fractions provides a robust measure of the low-frequency fluctuations in temperature non-uniformities in the flow. Measurements in a scramjet test rig indicate a distinct increase in low-frequency fluctuations of low-temperature gases several seconds before the isolator shock train is forced out of the inlet by heat addition to the combustor. Though the precise cause of the fluctuations remains unknown, the detection method shows promise for use in control schemes to avoid back pressure-induced unstarts.     

Quantum cascade laser-based sensor for detection of exhaled and biogenic nitric oxide

A real-time, in situ CO sensor using 2.3 μm DFB diode laser absorption, with calibration-free wavelength-modulation-spectroscopy, was demonstrated for continuous monitoring in the boiler exhaust of a pulverized-coal-fired power plant up to temperatures of 700 K. The sensor was similar to a design demonstrated earlier in laboratory conditions, now refined to accommodate the harsh conditions of utility boilers. Measurements were performed across a 3 m path in the particulate-laden economizer exhaust of the coal-fired boiler. A 0.6 ppm detection limit with 1 s averaging was estimated from the results of a continuous 7-h-long measurement with varied excess air levels. The measured CO concentration exhibited expected inverse trends with the excess O₂ concentration, which was varied between 1 and 3 %. Measured CO concentrations ranged between 6 and 200 ppm; evaluation of the data suggested a dynamic range from 6 to 10,000 ppm based on a minimum signal-to-noise ratio of ten and maximum absorbance of one. This field demonstration of a 2.3 μm laser absorption sensor for CO showed great potential for real-time combustion exhaust monitoring and control of practical combustion systems.     

Potential interference mechanism for the detection of explosives via laser-based standoff techniques

A variety of laser-based standoff techniques are currently being developed for the detection of explosives. Many approaches focus on the detection of NO as an indicator for the presence of nitro-based explosives. One of these approaches uses lasers to vaporize the explosive molecules residing at or near a surface, photo-dissociate the molecules resulting in vibrationally hot NO, and then perform laser-induced fluorescence on the vibrationally hot NO. Most related reports have focused on using 236 nm or 247–248 nm for the laser excitation of vibrationally hot NO. In addition, a recent report suggests the use of 532 nm to desorb, vaporize, and photo-fragment explosive samples. We report here on energy transfer from laser-excited N₂ to NO and its consequences for the detection of nitro-based explosives. A potential interference mechanism was found for using 532 nm and 236 nm. The interference mechanism is based upon multi-photon excitation (532 nm) or two-photon excitation (236 nm) into excited states of molecular nitrogen and subsequent energy transfer from nitrogen to NO, followed by NO luminescence. Such interference mechanisms highlight the complexity of the explosive detection problem and the need for complementary approaches to improve the detection capabilities.     

高分辨紫外电子轰击互补金属氧化物半导体器件的实验研究

基于真空紫外光电阴极和背照式互补金属氧化物半导体(CMOS)图像传感器研制了紫外光响应的电子轰击CMOS(EBCMOS)器件,实现了EBCMOS器件在40 mlx光照度环境下的高分辨探测,电子图像灰度随电子能量的变化呈现出极好的线性关系.对器件成像分辨率测试的结果表明,在电场强度为5000 V/mm时,器件的空间分辨率可以达到25 lp/mm,与国际相关报道水平相当.研制的EBCMOS器件可直接在紫外弱光探测领域应用,如天文观察、高能物理、遥感测绘等,同时也可为下一步研制可见光和近红外敏感的EBCMOS器件提供参考.     

High resolution NMR spectroscopy of rat brain in vivo through indirect zero-quantum-coherence detection

The time evolution of zero-quantum-coherences (ZQCs) is insensitive to magnetic field inhomogeneity. Using a 2D indirect ZQC detection method it is shown that high-resolution (1)H NMR spectra can be obtained from rat brain in vivo at 11.74T that are immune to magnetic field inhomogeneity. Simulations based on the density matrix formalism, as well as in vitro measurements are used to demonstrate the features of 2D ZQC NMR spectra. Unique spectral information which is normally not directly available from regular (1)H NMR spectra can be extracted and used for compound identification or improved prior knowledge during spectral fitting.     

High resolution digital holography

In digital Fresnel holography, present specifications of charge-coupled device cameras require the incident beams to be quasi-parallel. That implies large speckle grain size and low lateral resolution in reconstructed images. Better lateral resolutions are demonstrated in our work, down to 8 μm, allowing the observation of sub-millimetre objects by digital holography. The experimental set-up built samples the incident light distribution with a definition of 500 pixels mm⁻¹. The maximum acceptable angle is then widened and the hologram recording and reconstruction distances are drastically reduced, as well as the speckle size. Interferometric holography was implemented for the measurement of the deformation of a sub-millimetre silicon cantilever and results in phase-contrasts imaging are also reported. The design of dedicated complementary metal-oxide-semiconductor active pixel sensor cameras is also discussed.     

High resolution spectroscopy of and

Extensions in frequency coverage coupled with sensitive spectroscopic techniques have enabled high resolution measurements of pure rotational spectra of deuteromethane and its 13-C substituted counterpart up to J^′=7. The current work reveals a small inconsistency in previously reported frequency measurements of ¹²CH₃D at J^′=5.     

Quantum cascade laser-based carbon monoxide detection on a second time scale from human breath

We present three different detection schemes for measuring carbon monoxide (CO) in direct absorption using a thermoelectrically cooled, distributed-feedback pulsed quantum cascade (qc) laser operating between 2176 and 2183 cm^-1. The laser emission has overlap with the strong R(8)1 ro-vibrational transition in CO at 2176.2835 cm^-1. Firstly, by utilizing the frequency chirp of the qc-laser with long laser pulses, a minimal detectable absorption of 1.2×10^-5 cm^-1 is achieved at an acquisition rate of 3 Hz. Additionally, with short laser pulses and slow frequency scanning a minimal detectable absorption 8.2×10^-7 cm^-1 is reported, with an acquisition time of 60 s. Finally, a novel amplitude modulation technique is developed to facilitate real-time measurement of CO in exhaled air. The application of this detector to detection of CO in a single breath as a potential non-invasive diagnostic tool is shown. PACS 07.07.Df; 42.62.Be     

Optical and electronic design for a field prototype of a laser-based vehicle delineation detection system

A field prototype of a laser-based non-intrusive vehicle detection system has been developed for the measurement of delineations of moving vehicles on the highway. This prototype is based on our previous research on the principle of the measurement. The detection system uses two laser lines that are projected onto the ground as probes. The reflected light is collected and focused onto a photodiode array by an optical system. Vehicle presence is detected based on the absence of reflected laser light. By placing two identical laser/sensor pairs at a known distance apart, the speed of both the front and rear of a vehicle can be calculated based on the times when each sensor is triggered. The detector data are acquired and processed by a real-time system to obtain speed, acceleration, and length of a detected vehicle. The travel time of a vehicle can be acquired by detecting a vehicle at the beginning of a link and re-identifying the same vehicle at the end of the link. Several tests have been done with the field prototype system on the highway. The testing results show that the system can obtain the accuracy of measurement necessary to distinguish between moving vehicles on the highway. This article describes the design and implementation of each functional component of an advanced version of the field prototype system.     

High resolution spectroscopy using photodeflection

Isotope separation by laser deflection of an atomic beam, combined with simultaneous mass spectroscopy, has been used to determine optical frequency shifts and to assign mass numbers to all components of the $\text{Ba 6s}{}^2{}^1\text{S}{}_0\text{?6s6p}{}^1\text{P}{}_1$ 5536 Å resonance. Several components which cannot be resolved optically without the use of enriched samples, were resolved with the technique described. They are ${}^{135}\text{Ba}\text{(F=}\text{5}\text{2}\text{)}$ at 120 MHz, ¹³⁶Ba at 128 MHz and ¹³⁴Ba at 138 MHz.     

High resolution spectroscopy with lasers

A review is given about recent applications of lasers in high resolution spectroscopy including methods with high spectral- or high time-resolution. Following a short survey about the characteristic features of lasers important for spectroscopic research, some examples are discussed where lasers were used in molecular emission- and absorption-spectroscopy. New techniques are outlined which overcome the Doppler-limitation in spectral resolution as for instance saturation-spectroscopy, level crossing or double-resonance-techniques. Some experiments are mentioned where the capability of lasers in producing ultrashort optical pulses are used for subnanosecond spectroscopy.     

High resolution infrared spectrum of silane

The infrared absorption spectrum of SiH₄ in the 4200–4500 cm^?1 region has been recorded using a high resolution grille-spectrometer. Two bands have been observed and identified as 2ν₃ and ν₁ + ν₃. Some molecular constants have been calculated, using the formalism developed by Jacques Moret-Bailly.     

High resolution print-patterning of a nano-suspension

In this paper we report a breakthrough in accurately print-patterning features from a nano-suspension. Twenty nanometer size equiaxed silica particles dispersed in a liquid medium were subjected to electrohydrodynamic forces and the type of jetting observed was mapped over a pico to femto flow rate regime-electric field parametric space. In the stable cone-jet mode, ∼60 μm features are patterned using a unique but simple, computer-controlled device. By reducing the flow rate by a further three orders of magnitude, a fine jet can be generated instantaneously and we are able to exploit this and accurately position ∼13 μm diameter equiv-spaced droplet-relics, which contain a dense assembly of the nanoparticles. We also demonstrate drawing of ∼17 μm wide lines of the nano-suspension.This revised version was published online in August 2005 with a corrected issue number.