共查询到20条相似文献,搜索用时 31 毫秒
1.
We show that the propagation of coherent acoustic phonons generated by femtosecond optical excitation can be clearly resolved using a probe laser in the middle UV (MUV) range. The MUV probe is easily produced from a high-repetition-rate femtosecond laser and a homemade frequency tripler. We present various experimental results that demonstrate efficient and high frequency detection of acoustic phonons. Thus, we show that the MUV range offers a unique way to reach higher frequencies and probe smaller objects in ultrafast acoustics. 相似文献
2.
We report the detection of linear optical diffraction of a He-Ne laser probe beam from a monolayer grating of molecular adsorbates up to the fifth order with no electronic or electromagnetic enhancement. The advantages of using linear diffraction to probe surface diffusion of adsorbates are discussed. 相似文献
3.
A new nonlinear Raman spectroscopy technique for trace-gas detection was proposed and demonstrated. The technique involved the use of a thermal-lens detection scheme to monitor thermal emission from the stimulated Raman process. We termed this technique thermal-lens Raman spectroscopy, and it was combined with a novel scheme involving a nonlinear Raman spectroscopy without a tunable laser. This technique was applied to detecting trace hydrogen molecules in the atmosphere by use of a pulsed Nd:YAG laser and a continuous-wave He-Ne probe laser. A detection limit of 9 parts in 10(6) was attained. 相似文献
4.
We present experimental results concerning the laser generation of picosecond acoustic pulses and their propagation in isotropic and anisotropic materials. We make use of a conventional reflectance detection technique as well as interferometric detection to probe the real and imaginary changes in reflectance. We also demonstrate the detection of transverse acoustic waves by mode conversion at an interface between an isotropic polycrystalline film and an anisotropic substrate. 相似文献
5.
K. Fukuda A. Toriyama A. Ch. Izmailov M. Tachikawa 《Applied physics. B, Lasers and optics》2005,80(4-5):503-509
We carried out experimental and theoretical research on dark Raman resonances in the absorption of the probe monochromatic wave in a thin vapor cell, whose length is much less than the diameters of probe and coupling laser beams. In this case, only the slow atoms have enough time to settle down to the dark quantum state during a free flight between the end walls of the cell. As a result, a sub-Doppler structure is observed when one sweeps both the coupling and probe laser frequencies keeping the Raman resonance condition. Second harmonic lock-in detection is used to evaluate sharpness of the dark-resonance line. The cell-length dependence of the observed spectral profile is satisfactorily reproduced by the steady-state analysis of the density matrix in which the velocity-dependent transit time effect is taken into account. 相似文献
6.
Rok Petkovšek Aleš Babnik Janez Diaci Janez Možina 《Applied Physics A: Materials Science & Processing》2008,93(1):141-145
We present a new method for monitoring of the laser micro-drilling process. The method is based on detection of acoustic waves
in air above the processed sample using a laser beam deflection probe (LBDP). We present an augmentation of the experimental
set-up by means of a digital micrographic system which enables the acquisition of images of the plasma plume and of the hole
cross-section during a drilling sequence. Comparing the acquired images with the detected LBDP signals, we examine the drilling
process from a new perspective. 相似文献
7.
We investigate quantum optical behaviors of a weak-probe laser field in an asymmetric semiconductor three-coupled-quantum wells (TCQW) structure based on intersubband transitions (ISBTs) via switch-on/off of terahertz (TH) signal radiation under the application of a control laser field. A scheme for TH signal detection and its strength measurement based on this probe absorption characteristic also are put forward, where TH signal field does not interact directly with electron, but significantly affects the coherent optical absorption properties of such a weak-probe laser field. Consequently, the proposed TCQW nanostructure may be used for reducing and cancelling out the important thermionic dark current component in the process of TH signal detection, measurement and photodetector design. 相似文献
8.
We report the experimental results and theoretical analysis of broadband detection of terahertz (THz) waves via electric-field-induced second-harmonic generation in laser-induced air plasma with ultrashort laser pulses. By introducing the second-harmonic component of the white light in the laser-induced plasma as a local oscillator, coherent detection of broadband THz waves with ambient air is demonstrated for the first time. Our results show that, depending on the probe intensity, detection of THz waves in air can be categorized as incoherent, hybrid, and coherent detection. Coherent detection is achieved only when the tunnel ionization process dominates in gases. 相似文献
9.
Hayley Newton Laura L. Walkup Nicholas Whiting Linda West James Carriere Frank Havermeyer Lawrence Ho Peter Morris Boyd M. Goodson Michael J. Barlow 《Applied physics. B, Lasers and optics》2014,115(2):167-172
Spin-exchange optical pumping (SEOP) has been widely used to produce enhancements in nuclear spin polarisation for hyperpolarised noble gases. However, some key fundamental physical processes underlying SEOP remain poorly understood, particularly in regards to how pump laser energy absorbed during SEOP is thermalised, distributed and dissipated. This study uses in situ ultra-low frequency Raman spectroscopy to probe rotational temperatures of nitrogen buffer gas during optical pumping under conditions of high resonant laser flux and binary Xe/N2 gas mixtures. We compare two methods of collecting the Raman scattering signal from the SEOP cell: a conventional orthogonal arrangement combining intrinsic spatial filtering with the utilisation of the internal baffles of the Raman spectrometer, eliminating probe laser light and Rayleigh scattering, versus a new in-line modular design that uses ultra-narrowband notch filters to remove such unwanted contributions. We report a ~23-fold improvement in detection sensitivity using the in-line module, which leads to faster data acquisition and more accurate real-time monitoring of energy transport processes during optical pumping. The utility of this approach is demonstrated via measurements of the local internal gas temperature (which can greatly exceed the externally measured temperature) as a function of incident laser power and position within the cell. 相似文献
10.
We demonstrate the lossless state-selective detection of a single rubidium 87 atom trapped in an optical tweezer. This detection is analogous to the one used on trapped ions. After preparation in either a dark or a bright state, we probe the atom internal state by sending laser light that couples an excited state to the bright state only. The laser-induced fluorescence is collected by a high numerical aperture lens. The single-shot fidelity of the detection is 98.6±0.2% and is presently limited by the dark count noise of the detector. The simplicity of this method opens new perspectives in view of applications to quantum manipulations of neutral atoms. 相似文献
11.
Remote detection and identification of biological aerosols using a femtosecond terawatt lidar system
We demonstrate experimentally the first range-resolved detection and identification of biological aerosols in the air by non-linear lidar. Ultra-short terawatt laser pulses are used to induce two-photon-excited fluorescence (2PEF) in riboflavin-containing particles at a remote location. We show that, in the case of amino acid detection, 2PEF-lidar should be more efficient than linear 1PEF-lidar beyond a typical distance of 2 km, because it takes advantage of the higher atmospheric transmission at the excitation wavelengths. 2PEF-lidar moreover allows size measurement by pump–probe schemes, and pulse shaping may improve the detection selectivity. PACS 33.50.-j; 33.80.Wz; 42.65.-k; 42.68.Wt; 92.60.Mt 相似文献
12.
An inspection of mechanically damaged areas on manufactured metal parts is necessary to produce high-quality products. A scanning probe on a sample is necessary for a conventional surface inspection system, which is time-consuming. We propose a novel high-speed detection method for defects on metal surfaces with rolling indentations. To obtain a large field of view in a measurement, we used a laser sheet that was expanded with a laser line generator and also used an expanded collimated beam, rather than a small laser spot as used in conventional techniques. Furthermore, we used an obliquely incident laser beam to suppress the effect of the rolling indentations surrounding defects, and also applied spatial frequency filtering to extract only defects. The spatial frequency filtering under oblique incidence is theoretically explained and defect extraction was investigated in experiments. 相似文献
13.
We introduce an imaging technique that combines complementary features of ultrasound and near-infrared diffusive light imaging. We achieve the combined technology experimentally by mounting an ultrasound array together with multiple laser source and optical detector fibers upon a hand-held probe. The technique is demonstrated with tissue phantoms wherein both acoustic and optical sensors image the volume underneath the probe. Coregistration of acoustic and optical images is achieved with an accuracy of 0.27+/-0.20cm, approximately half of the image pixel size of our prototype. Accurate determination of target optical absorption is also achieved by use of image segmentation on the ultrasound reconstruction. The combined technique may provide improved breast-cancer detection sensitivity and specificity. 相似文献
14.
We investigate the absorption spectra of a probe laser in warm rubidium atoms driven into the four-level N configuration. Our numerical calculations show that there are six (two) coherent hole-burnings and one (two) transparency window(s) in the probe absorption spectra, when the perturbing laser co-propagates (counter-propagates) with the probe laser and both coupling and saturating lasers are exactly resonant with their driving transitions. Gradually weakening the perturbing laser, we can dramatically change the probe absorption spectra to observe more coherent hole-burnings and transparency windows as well as the conversion from transparency windows into coherent hole-burnings. Relevant phenomena can be well understood in the dressed state representation. 相似文献
15.
We present a novel method for quantifying low concentrations of DNA based on single molecule detection (SMD) for molecular
counting and flow measurements inside a microchannel. A custom confocal fluorescence spectroscopic system is implemented to
detect fluorescent bursts emitted from stained DNA molecules. Measurements are made one molecule at a time as they flow through
a femtoliter-sized laser focal probe. Durations of single molecule fluorescent bursts, which are found to be strongly related
to the molecular transit times through the detection region, are statistically analyzed to determine the in situ flow speed
and subsequently the sample volume flowing through the focal probe. Therefore, the absolute concentration of a DNA sample
can be quantified based on the single molecule fluorescent counts from the DNA molecules and the associated probe volume for
a measured time course. To validate this method for quantifying low concentrations of biomolecules, we tested samples of pBR322
DNA ranging from 1 pM to 10 fM (∼3 ng/ml to 30 pg/ml). Besides molecular quantification, we also demonstrate this method to
be a precise and non-invasive way for flow profiling within a microchannel. 相似文献
16.
17.
Multi-target ranging using an optical reservoir computing approach in the laterally coupled semiconductor lasers with self-feedback 下载免费PDF全文
Dong-Zhou Zhong 《中国物理 B》2022,31(7):74205-074205
We utilize three parallel reservoir computers using semiconductor lasers with optical feedback and light injection to model radar probe signals with delays. Three radar probe signals are generated by driving lasers constructed by a three-element laser array with self-feedback. The response lasers are implemented also by a three-element lase array with both delay-time feedback and optical injection, which are utilized as nonlinear nodes to realize the reservoirs. We show that each delayed radar probe signal can be predicted well and to synchronize with its corresponding trained reservoir, even when parameter mismatches exist between the response laser array and the driving laser array. Based on this, the three synchronous probe signals are utilized for ranging to three targets, respectively, using Hilbert transform. It is demonstrated that the relative errors for ranging can be very small and less than 0.6%. Our findings show that optical reservoir computing provides an effective way for applications of target ranging. 相似文献
18.
基于可调谐半导体激光吸收光谱技术及波长调制技术,采用波长为1 654 nm的分布反馈激光器,结合开放式光学探头以及高灵敏度的铟镓砷光电探测器,研制了近红外甲烷气体检测系统。自主设计研发了分布反馈激光器驱动电路,主要包括模拟PID温度控制电路与电流驱动电路。其中,温度控制电路具有较高的控制精度及稳定性,长时间工作时激光器温度波动小于±0.02 ℃,温度与激光器波长呈线性变化。温度不变时,改变驱动电流可以使激光器中心波长线性变化,同时还提供了5 kHz正弦波和10 Hz锯齿波的调制信号,用于谐波检测。为了提取差分信号的一次谐波及二次谐波,研制了正交锁相放大器,一次谐波和二次谐波的提取误差分别为3.5%和5%。系统中采用的开放式光电探头通过一次反射,使有效吸收光程增加了一倍,达到了40 cm。通过对1%~5%的甲烷气体进行检测,成功提取了一次及二次谐波,得到了气体浓度与谐波信号幅值的拟合关系曲线。在更换不同输出波长的激光器后,该系统还具有检测其他气体的能力。 相似文献
19.
We describe an array of spin-exchange-relaxation-free optical magnetometers designed for detection of fetal magnetocardiography (fMCG). The individual magnetometers are configured with a small volume with intense optical pumping, surrounded by a large pump-free region. Spin-polarized atoms that diffuse out of the optical pumping region precess in the ambient magnetic field and are detected by a probe laser. Four such magnetometers, at the corners of a 7 cm square, are configured for gradiometry by feeding back the output of one magnetometer to a field coil to null uniform magnetic field noise at frequencies up to 200 Hz. We present the first measurements of fMCG signals using an atomic magnetometer. 相似文献
20.
In this contribution the first measurements of a single-shot femtosecond laser pump–probe technique are reported. The technique
is based on counter-propagating femtosecond laser pulses in a supersonic beam of a low density of sample molecules and simultaneous
probe detection by ion or fragment-ion formation through a reflectron time-of-flight mass spectrometer. It will be shown that
the range of the pump–probe delays covers the time span between 100 fs and 10 ps depending on the pulse width of the laser
used and the stability of the volt ages of the mass spectrometer. The application of this technique to organometallic compounds
as well as to medium-sized organic molecules reveals some insight into the electron-transfer process during ionization through
a 1+1 multi-photon absorption procedure. Furthermore it is demonstrated that this technique is also applicable to the investigation
of ultra-fast isomerization and fragmentation processes. As an example the results of the processes within iron pentacarbonyl
and substituted benzalacetones are reported.
Received: 22 October 1999 / Published online: 24 July 2000 相似文献