Shenggang Liu

Note: Using an optical phase–locked loop in heterodyne velocimetry

An optical phase-locked loop was introduced in heterodyne velocimetry to lock the differential frequency between a fiber laser and an external cavity diode laser. An uncertainty less than 1 MHz of the locked beat frequency was achieved during several microseconds, corresponding to a velocity uncertainty at 0.1 m/s level for 1550 nm light. In this way, a measurement with higher precision and better time resolution simultaneously can be obtained during a transient process. Three proof-of-principles shots were performed to measure elastic wave-induced vibrations on surfaces of steel films with submillimeter thicknesses. The surface velocity fluctuations were probed with amplitudes of about 2 m/s and periods of tens of nanoseconds, and propagating times and sound velocities of waves were also well analyzed at a time scale 0.5 μs. A velocity resolution of 0.1 m/s level and a temporal resolution of a few nanoseconds were achieved in these measurements.

Optical-fiber frequency domain interferometer with nanometer resolution and centimeter measuring range

A new optical-fiber frequency domain interferometer (OFDI) device for accurate measurement of the absolute distance between two stationary objects, with centimeter measuring range and nanometer resolution, has been developed. Its working principle and on-line data processing method were elaborated. The new OFDI instrument was constructed all with currently available commercial communication products. It adopted the wide-spectrum amplified spontaneous emission light as the light source and optical-fiber tip as the test probe. Since this device consists of only fibers or fiber coupled components, it is very compact, convenient to operate, and easy to carry. By measuring the single-step length of a translation stage and the thickness of standard gauge blocks, its ability in implementing nanometer resolution and centimeter measuring range on-line measurements was validated.

Note: A novel method to measure the deformation of diamond anvils under high pressure

A novel and simple method based on optical-fiber frequency domain interferometer to measure the deformation of diamond anvils under high pressure is presented. The working principle and application examples are given in this paper. The deformation of diamond anvils is obtained up to 37.7 GPa, our results verify that the deformation has an obvious difference between uploading and downloading at a given pressure, the maximum difference is up to 4.5 μm at 18.8 GPa, and the cupping effect is observed directly.

Dynamic frequency-domain interferometer for absolute distance measurements with high resolution

A unique dynamic frequency-domain interferometer for absolute distance measurement has been developed recently. This paper presents the working principle of the new interferometric system, which uses a photonic crystal fiber to transmit the wide-spectrum light beams and a high-speed streak camera or frame camera to record the interference stripes. Preliminary measurements of harmonic vibrations of a speaker, driven by a radio, and the changes in the tip clearance of a rotating gear wheel show that this new type of interferometer has the ability to perform absolute distance measurements both with high time- and distance-resolution.

Simultaneous measurement of the dynamic emissivity and the radiance of the shocked Al/LiF interface in the near-infrared wavelength

A novel method based on signal superimposing has been presented to simultaneously measure the dynamic emissivity and the radiance of a shocked sample/window interface in the near-infrared wavelength. In this method, we have used three rectangle laser pulses to illuminate the sample/window interface via an integrating sphere and expect that the reflected laser pulses from the sample/window interface can be superimposed on its thermal radiation at the shocked steady state by time precision synchronization. In the two proving trials, the second laser pulse reflected from the Al/LiF interface has been successfully superimposed on its thermal radiation despite large flyer velocity uncertainty. The dynamic emissivity and the radiance at 1064 nm have been obtained simultaneously from the superimposing signals. The obtained interface temperatures are 1842 ± 82 K and 1666 ± 154 K, respectively, the corresponding release pressures are 65.7 GPa and 62.6 GPa, and the deduced Hugonoit temperatures are consistent with the theoretical calculations. In comparison, the fitting temperatures from the gray body model are 300-500 K higher than our experimental measurement results and the theoretical calculations.

A simple and reliable implementation of all-fiber velocity interferometer

This work reports a fiber velocity interferometer (FVI), mainly used for velocity profile measurements of materials in dynamic compression experiments. This FVI generates two pairs of orthogonal signals with only one fiber-coupled optical hybrid to achieve push–pull analysis, which is traditionally obtained by a set of discrete optical components in a velocity interferometer system for any reflector (VISAR). These signals are received differentially by two balanced detectors. Common mode fluctuations of signals caused by rapid changes in light intensity are suppressed in this way, and the signals will not easily exceed the dynamic range of recorders anymore. Furthermore, a dual-core fiber probe is used to reduce disturbance from unwanted lights. At the Institute of Fluid Physics, FVI has been successfully applied in high-speed measurements up to several kilometers per second with almost the same precision of the heterodyne velocimetry (HV), which is now considered to be a reliable and accurate technique.