Common-path heterodyne laser-induced thermal acoustics for seedless laser velocimetry

We demonstrate the use of a novel technique for the detection of heterodyne laser-induced thermal acoustic signals that allows the construction of a highly stable seedless laser velocimeter. A common-path configuration is combined with quadrature detection to provide flow direction, to greatly improve robustness to misalignment and vibration, and to give reliable velocity measurement at low-flow velocities. Comparison with Pitot tube measurements in the free stream of a wind tunnel shows root-mean-square errors of 0.67 m/s over the 0-55-m/s velocity range.     

Retrodiction for coherent communication with homodyne or heterodyne detection

Previous work on the retrodictive theory of direct detection is extended to cover the homodyne detection of coherent optical signal states and . The retrodictive input state probabilities are obtained by the application of Bayes' theorem to the corresponding predictive distributions, based on the probability operator measure (POM) elements for the homodyne process. Results are derived for the retrodictive information on the complex amplitude of the signal field obtainable from the difference photocount statistics of both 4-port and 8-port balanced homodyne detection schemes. The local oscillator is usually assumed much stronger than the signal but the case of equal strengths in 4-port detection is also considered. The calculated probability distributions and error rates are illustrated numerically for values of signal and local oscillator strengths that extend from the classical to the quantum regimes.     

Phase-shifting interferometry with feedback control using heterodyne phase detection

A phase-shifting interferometer with feedback control using heterodyne phase detection was developed. A composite heterodyne phase detection method for obtaining feedback signals was proposed. Interference fringe stabilization and accurate pi/2 phase shifts under micrometer-order vibrations were successfully demonstrated using a digital high-speed lock-in amplifier.     

Optical heterodyne detection of laser-induced gratings

A novel optical arrangement for heterodyne detection of laser-induced gratings based on the use of a phase mask for both excitation and probe beams provides phase stability and control without the need for an active stabilization scheme. The arrangement greatly simplifies the laser-induced grating experiment. The performance of the technique in both transmission and reflection geometries is illustrated through measurements of bulk and surface acoustic waves generated by picosecond laser pulses.     

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.     

Thermal emission detection by laser heterodyne radiometry

A selective black body is considered as a self-emitting source and can be characterized by its remote thermal emission. This emission is detected at 10 μm wavelength by a laser heterodyne radiometer. Temperature, spectral, and spatial resolution conditions are given. The experimental set-up is fully described and signal-to-noise ratio measurements are presented.     

Observations de non-linearites en detection heterodyne infrarouge

Résumé Des expériences de détection hétérodyne ont été effectuées, dans l'infrarouge, avec trois montages optiques différents un interféromètre de Michelson modifié et deux montages utilisant l'amplification de la puissance rétrodiffusée dans la cavité laser. A partir de la rétrodiffusion sur un disque en rotation, on étudie la réponse du système en fonction de la fréquence de battement. L'évolution du signal n.est pas linéaire. Cette non linéarité provient de l'interaction de l'onde diffusée avec le milieu laser. A partir de ces résultats, on présente un prototype d'anémomètre à laser capable de mesurer des vitesses de vent jusqu'à 40 km/h à une distance de 500 mètres.

---

Some infrared heterodyne detection experiments have been performed with a modified Michelson interferometer and two systems of back-scattered radiation amplified in the laser cavity. The frequency responses have been studied using the radiation scattered from a rotating wheel. The evolution is nonlinear with the frequency and seems to originate in the interaction of the back-scattered wave with the laser itself. Taking into account these results, a laser anemometer is presented, capable of detecting aerosols as far as 500 metres away.

     

IQ quadrature demodulation algorithm used in heterodyne detection

In order to obtain better detection results of heterodyne, we used phase IQ quadrature demodulation algorithm to process the data which detected by laser heterodyne. Based on laser heterodyne interferometer, processing the data in the interferometer phase IQ quadrature demodulation algorithm from the signal to noise ratio, sampling rate, sampling rate, filter order and cutoff frequency, verify the effects of these system parameters to the phase precision, and choose the best parameters to obtain a better phase precision through experiment as: the signal to noise ratio is 25 dB, the IF signal frequency is 98.3 MHz, 98.5 MHz, 99.1 MHz, 99.5 MHz and 100 MHz, the sampling rate is 512–2048, the cutoff frequency and order of the filter are 0.11 and 40, respectively.     

Pulsed acousto-optic imaging in dynamic scattering media with heterodyne parallel speckle detection

We present a new detection scheme for acousto-optic tomography based on pulsed-wave ultrasound and illumination combined with heterodyne parallel speckle detection. This setup can perform tomographies inside several-centimeter-thick scattering samples. Test experiments confirm the suitability of this method for performing tomographies inside various types of optically scattering media, including liquids.     

Laboratory and atmospheric ozone measurements by infrared-laser heterodyne detection

A laser-heterodyne spectrometer with a resolution of 5 MHz has been used to record laboratory and atmospheric spectra of ozone in the 10 m region. The necessary parameters to process the atmospheric spectra are defined through the laboratory spectra. The atmospheric ozone concentration versus altitude and the atmospheric CO₂ volume mixing ratio have been obtained.     

Transmittance and phase measurement via self-calibrated balanced heterodyne detection

It is rare for a conventional direct detection method to measure the transmittance uniformity of mirrors with rigorous standards, especially to meet the requirement of transmittance/reflectance and phase detection simultaneously. In this study, a new method of self-calibrated balanced heterodyne detection(SCBHD) is proposed. It can be self-calibrated by a two-channel structure to overcome the environmental effects in large optics scanning detection by employing highly accurate heterodyne interference. A typical transmittance measurement experiment was performed at 1053 nm wavelength via SCBHD. A standard deviation(SD) of 0.038% was achieved in the preliminary experiment. The experimental results prove to reduce the SD by approximately two orders of magnitude compared with the conventional direct detection method in the same condition. The proposed method was verified as being promising not only for its wider dynamic measurement range and its higher accuracy but also for its simultaneous transmittance and phase detection ability.     

Excess-noise suppression in a fibre-optic balanced heterodyne detection system

We have investigated balanced heterodyne detection in applications where laser intensity fluctuations are the dominant noise source, as, for example, in laser Doppler velocimetry with a He-Ne laser. The suppression of excess noise in comparison with a single receiver detection system is analysed theoretically. In our heterodyne experiment we have compared two different fibre-optic Mach-Zehnder interferometers, both with single-mode polarization-preserving fibres, one in integrated form using a directional coupler, the other one with a dielectric beam-splitter as the optical mixing element. With the former we have verified the theoretical results; with the latter we have demonstrated that with a good balance the fundamental short noise detection limit can be reached.     

Absolute phase measurement in heterodyne detection of transient gratings

We present a method of measuring the absolute phase in heterodyne-detected transient grating experiments. The method permits direct and sensitive characterization of the amplitude and phase of the grating parameters. We also present a convenient implementation of this technique and demonstrate its efficacy in a cuprate superconductor.     

外差探测系统中马卡望远镜离轴使用的研究

鉴于马卡望远镜离轴能够减小因副镜遮挡引起的光能量损失,分析了马卡望远镜离轴使用时,合作目标和非合作目标发射和接收光路的区别。讨论了马卡望远镜在外差探测系统离轴使用时,发射能量提高,但外差效率下降的原因;在合作目标外差探测系统离轴使用时发射能量提高30%以上,外差效率也有很大提高;通过对散射体目标物和平面镜的测量,分别得到了17%和85%的外差效率,验证了马卡望远镜在合作目标外差探测系统中可以离轴使用。     

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.     

Full-field optical coherence tomography by two-dimensional heterodyne detection with a pair of CCD cameras

A two-dimensional heterodyne detection technique based on the frequency-synchronous detection method [Jpn. J. Appl. Phys. 39, 1194 (2000)] is demonstrated for full-field optical coherence tomography. This technique, which employs a pair of CCD cameras to detect the in-phase and quadrature components of the heterodyne signal simultaneously, offers the advantage of phase-drift suppression in interferometric measurement. Horizontal cross-sectional images are acquired at the rate of 100 frames/s in a single longitudinal scan, with a depth interval of 6 microm, making the rapid reconstruction of three-dimensional images possible.