Numerical heterodyne holography with two-dimensional photodetector arrays

We present an original heterodyne holography method for digital holography that relies on two-dimensional heterodyne detection to record the phase and the amplitude of a field. The technique has been tested on objects as much as 13 mm in size. Consistency checks were performed, and high-resolution images were computed. We show the requirement for a spatial filter to select properly sampled near-axis photons. Heterodyne holography is superior to off-axis digital holography for both field of view and resolution.     

逆合成孔径成像激光雷达数据采样技术

逆合成孔径成像激光雷达能够实现对运动目标的高分辨实时成像,但激光信号的极大带宽和目标回波信号的微弱性给雷达回波数据的接收和处理带来了较大困难.针对这一问题,提出了基于光外差探测手段和压缩感知理论相结合的信号采样方法,首先通过光外差探测降低回波信号的有效带宽,再结合压缩感知理论实现对信号的稀疏化采样和重构.仿真结果证明了运用本文所提出的采样方法,在使用远低于奈奎斯特定理所规定的采样率时,仍然能够实现对目标的高质量成像.     

Laser computed tomography of opaque industrial products measured by coherent detection imaging method

The coherent detection imaging method with a low-power He–Ne laser as the source is used to obtain transillumination laser computed tomographic and two-dimensional (2D) images of opaque industrial products such as fluorescent lamps and electric light bulbs. This method is principally based on the optical heterodyne detection technique that has the highest sensitivity along with excellent selectivity in terms of coherence, polarization and high directionality. Structures of the filament and electrode enclosed in the opaque glass were clearly identified with submillimeter resolution.     

Two-dimensional coherent detection imaging in multiple scattering media based on the directional resolution capability of the optical heterodyne method

This paper describes a new application of optical heterodyne detection using a laser beam for two-dimensional imaging of the internal structure of strongly scattering media in which the structure is completely obstructed from normal visual observation. The directional resolution capability for image formation due to the excellent antenna properties of the heterodyne technique is verified experimentally using a ground glass to cause strong scattering of the signal beam. Successful image detection of a test target placed in a highly scattering absorptive medium, with spatial resolution better than 400 m in the case of our experiments, demonstrates that this Coherent Detection Imaging (CDI) method can overcome the diffuse nature of images in media such as those of biomedical interest and others to achieve scanning and tomographic imaging.     

Influence of Phase Drift on Optical Coherence Tomography Using a CCD Camera-Based Heterodyne Detection Technique

The performance of a two-dimensional heterodyne detection technique in optical coherence tomography (OCT) was studied. This technique, which is based on the frequency synchronous detection method, enables the use of an imager such as a charge coupled device (CCD) camera as a heterodyne sensor array, so that horizontal cross-sectional image can be acquired in real time without lateral scanning. OCT measurements of scattering media including a biological object were demonstrated. To evaluate the influence of phase fluctuations on the present technique, we measured and analyzed the statistical relative-standard-deviation of heterodyne signal intensity as a function of the random phase shifts between two consecutive CCD frames. Practical limitations in the signal stability and possible solutions are discussed.     

光外差-磁旋转-浓度调制光谱技术

介绍了一种针对瞬态分子光谱测量的新技术:光外差磁旋转浓度调制光谱技术,这种光谱技术具有很高的灵敏度,综合了光外差探测技术、磁旋转光谱技术和浓度调制光谱技术的特点,利用浓度调制光谱技术针对寿命很短的瞬态分子和激发态分子的光谱进行测量,利用光外差探测技术可以消除来自光源的幅度涨落噪声,实现散粒噪声的测量极限,利用磁旋转光谱技术可以对顺磁性分子进行选择性的测量,并且进一步提高探测灵敏度。详细讨论了这种光谱技术的工作原理,并用这种技术对O2分子的b1Σg+-X3Σg-三重禁戒跃迁光谱进行测量,获得了很好的测量信噪比。并对该技术的灵敏度作了详细的分析,估计最小相对吸收度可达1.9×10-9以及O2分子三重禁戒跃迁的吸收截面为σ=2.4×10-24cm2。     

Heterodyne detection of multiply scattered monochromatic light with a multipixel detector

A new technique is presented for measuring the spectral broadening of light that has been multiply scattered from scatterers in motion. In our method the scattered light is detected by a heterodyne receiver that uses a CCD as a multipixel detector. We obtain the frequency spectrum of the scattered light by sweeping the heterodyne local oscillator frequency. Our detection scheme combines a high optical etendue (product of the surface by the detection solid angle) with an optimal detection of the scattered photons (shot noise). Using this technique, we measure, in vivo, the frequency spectrum of the light scattered through the breast of a female volunteer.     

Heterodyne detection scheme for light-induced transient grating experiment

A novel heterodyne detection scheme for light-induced transient grating technique is presented. The heterodyne detection is achieved coherently mixing the picosecond pulses of diffracted and scattered light. A phase difference between these pulses is controlled by moving a holographic beam splitter along its grating vector. This approach is employed to study a competition of coexisting electronic and thermal optical nonlinearities in CVD grown diamond films in sub-nanosecond time domain and to determine carrier parameters.     

Raman heterodyne detected magnetic resonance: I. CW and coherent transient measurements

We report cw and coherent transient studies on electronic and nuclear magnetic transitions of the nitrogen-vacancy centre in diamond using an optical-rf double resonance technique: Raman heterodyne detection. Emphasis is placed on the coherent transient measurements to illustrate the versatility of the detection technique, which is not only very sensitive but is also ideal in this case since it is based on a coherent process. In this paper we show that Raman heterodyne detection can be used to obtain a wide range of signals including nutation, spin echo, rotary echo and spin locking in a single system. Finally an example of using coherent transients to test the validity of the Bloch equation is given.     

基于相位调制-解调的光纤激光相位噪声检测方法研究

在主动相位控制相干合成中,常用的光纤激光主动相位控制方法主要有外差法、多抖动法和随机并行梯度下降算法等. 基于多抖动法和外差法的原理,提出了一种新型的基于相位调制-解调的相位检测与控制方法. 该方法利用周期信号对参考光进行相位调制,将调制后的参考光与待检测信号光进行相干检测,通过对相干光强信号和相位调制信号的融合处理,实现相位噪声的检测和控制. 对该方法进行了数值模拟和实验研究. 实验结果表明,对于频率为2 kHz,噪声范围为[0,2π)的正弦噪声,相位检测精度优于λ/50,控制精度可达 关键词： 光纤激光 相干合成 相位噪声检测 调制-解调     

Application of the Raman heterodyne technique for the detection of EPR and ENDOR

Raman heterodyne detection is a coherent optical-RF double resonance technique where the optical and RF fields induce coherence within a three level system and a resultant Raman field is measured using heterodyne detection. This approach has been used previously to detect NMR and more recently EPR. In this paper the parameters that affect the amplitude and signal to noise ratio of the Raman heterodyne signals are considered. The power levels in relation to the oscillator strength and dephasing times, the amplitude and spectrum of the laser frequency jitter in relation to the optical homogeneous linewidths and holeburning rates, and the sample properties such as absorption strength and optical quality, are all factors that affect the Raman signal. The presentation is focused on the Raman heterodyne detected EPR of the nitrogen-vacancy pair centre in diamond making comparisons with Raman heterodyne detected NMR signals obtained for rare earth ion systems. RF-RF double resonance studies, RF holeburning and ENDOR, which give information about the hyperfine levels are also reported for the nitrogen-vacancy centre. The resonance frequencies are in agreement with those predicted from the spin Hamiltonian. The factors affecting the lineshapes and relative intensities of the double resonance signals are discussed.     

Heterodyne detection for Fiber Bragg Grating sensors

In this paper, we present a Fiber-Bragg-Grating-based temperature sensor. The technique employs heterodyne detection using two Fiber Bragg Gratings. One of the gratings is used as a reference (local oscillator) and the second as a sensing arm. This sensor uses a Folded Mach-Zehnder interferometer. As the temperature changes, the Bragg wavelength of the FBG shifts. The heterodyne detection is used to detect the frequency difference between the reference and sensing signals that is caused by the temperature change. The dynamic range and sensitivity of the sensor were analyzed and presented.     

一种新型外差光纤陀螺

本文提出了一种采用电光移频器和高双折射光纤构成的新型外差检测方式的光纤陀螺方案。它既能改善通常外差光纤陀螺中存在的光路非互易性且无需使用声光器件,又能避免采用高双折射光纤的直接检测光纤陀螺中电子线路直流漂移的影响。初步实验的结果显示出该系统具有良好的定标因子线性度。     

Heterodyne interferometric polarization coherent anti‐Stokes Raman scattering (HIP‐CARS) spectroscopy

We demonstrate a new technique that combines polarization sensitivity of the coherent anti‐Stokes Raman scattering (CARS) response with heterodyne amplification for background‐free detection of CARS signals. In this heterodyne interferometric polarization CARS (HIP‐CARS), the major drawbacks of polarization and heterodyne CARS are rectified. Using a home‐built picosecond optical parametric oscillator, we are able to address vibrational stretches between 600 and 1650 cm⁻¹ and record continuous high‐resolution Raman equivalent HIP‐CARS spectra. Copyright © 2010 John Wiley & Sons, Ltd.     

Heterodyne coherent anti-Stokes Raman scattering (CARS) imaging

We have achieved rapid nonlinear vibrational imaging free of nonresonant background with heterodyne coherent anti-Stokes Raman scattering (CARS) interferometric microscopy. This technique completely separates the real and imaginary responses of nonlinear susceptibility chi(3) and yields a signal that is linear in the concentration of vibrational modes. We show that heterodyne CARS microscopy permits the detection of weak vibrational resonances that are otherwise overshadowed by the strong interference of the nonresonant background.     

A white-light interferometer using a lamp source and heterodyne detection with acousto-optic modulators

A heterodyne technique for white-light interferometer with a lamp source, which uses two acousto-optic modulators, is developed for high-sensitivity detection of weak light. By using converging input beams input into a Michelson interferometer with spherical mirrors, the spectral dependence of the modulators is canceled, and the white-light heterodyne interference fringes are generated at 200 kHz. Using a tandem interferometer, the object surface which has a low surface reflectivity of less than 10⁻⁴ was detected with a good signal-to-noise ratio.     

Optical coherence topography based on a two-dimensional smart detector array

A low-coherence reflectometer based on a conventional Michelson interferometer and a novel silicon detector chip with a two-dimensional array of pixels that allows parallel heterodyne detection is presented. We demonstrate acquisition of three-dimensional images with more than 100,000 voxels per scan at a sensitivity of -58 dB and a rate of 6 Hz.     

调Q激光光折变自适应光外差探测技术研究

基于光折变晶体中自泵浦与互泵浦相位共轭共存效应,利用新型光折变自适应光外差探测系统进行了调Q脉冲激光的光折变自适应光外差探测技术研究.结果表明,该系统可以用来实现单纵模调Q脉冲激光的自适应光外差探测,并可以通过提高本振光强度有效地提高外差探测灵敏度.进一步的实验和理论分析表明,对于一般的调Q脉冲激光,由于其各个纵模频谱分量之间不相关,难于实现光外差探测.     

Dual-axes confocal microscopy with post-objective scanning and low-coherence heterodyne detection

We present a dual-axes confocal microscope that employs postobjective scanning and low-coherence heterodyne detection to collect vertical cross-sectional images from biological tissue with high axial resolution, reduced noise from scattered light, deep tissue penetration, and a large dynamic range. This architecture can be scaled down to millimeter dimensions with microelectromechanical systems technology for performance of in vivo optical biopsy.     

Frequency-multiplexed gas sensing using chirped laser molecular spectroscopy

A method for frequency-multiplexed multi-sample gas sensing is presented. It enables measuring multiple samples placed simultaneously in the setup, without any optical or mechanical switching. Samples are measured using heterodyne detection and signal from each sensing path is encoded at different carrier frequency. Subsequently, a signal from particular sample is retrieved through heterodyne beatnote demodulation at unique frequency. This technique is particularly suitable for real-time calibration of the sensor through a sequential (or simultaneous) detection of three signals: from unknown sample, reference sample and baseline. Basic setup is demonstrated and proof-of-concept experiments are presented. Very good agreement with spectra measured using standard tunable diode absorption spectroscopy is obtained.