Libing Ren

Absolute distance measurement using frequency-sweeping heterodyne interferometer calibrated by an optical frequency comb.

We present a frequency-sweeping heterodyne interferometer to measure an absolute distance based on a frequency-tunable diode laser calibrated by an optical frequency comb (OFC) and an interferometric phase measurement system. The laser frequency-sweeping process is calibrated by the OFC within a range of 200 GHz and an accuracy of 1.3 kHz, which brings about a precise temporal synthetic wavelength of 1.499 mm. The interferometric phase measurement system consisting of the analog signal processing circuit and the digital phase meter achieves a phase difference resolution better than 0.1 deg. As the laser frequency is sweeping, the absolute distance can be determined by measuring the phase difference variation of the interference signals. In the laboratory condition, our experimental scheme realizes micrometer accuracy over meter distance.

Five-degrees-of-freedom measurement system based on a monolithic prism and phase-sensitive detection technique

This paper presents a method for measuring five-degrees-of-freedom errors of a moving stage with a monolithic prism and phase-sensitive detection technique. It consists of a pigtailed laser diode, three position-sensitive detectors (PSDs), a monolithic prism, and additional optical and electronic components. The monolithic prism mounted on the moving stage generates three beams that are detected by three PSDs, respectively, so that the straightness, pitch, yaw, and roll errors can be simultaneously measured. Theoretical analysis of each error measurement process is presented. To reduce the influence of disturbing light, the laser diode is modulated by a sinusoidal wave current, and a phase-sensitive detection technique is developed to demodulate the signals. Compared with a laser interferometer, the deviation errors when measuring the horizontal and vertical straightness errors are better than ±0.25 and ±0.4 μm, respectively. The deviation errors for the pitch, yaw, and roll are better than ±0.5, ±0.3, and ±2 arc sec, respectively, in comparison with an autocollimator. The system can be assembled to measure five error components of machine tools in an industrial environment.

Frequency Comb Calibrated Diode Laser Interferometry for Absolute Distance Measurement

Real-time diode laser interferometry calibrated by a frequency comb is demonstrated by measuring the laser frequency trigger signal and the interference phase variations simultaneously, as the laser wavelength scans at a speed of 10 nm/s.

A Tele-Operated Gas Analyzer

A remote operable gas analyzer was designed and depicted in this paper. There’s no geographical restriction on using it and it’s easy to maintain. It’s especially suitable for long-term and large-scale detection of polluted gases.

Multi-component gas analyzer based on Fourier transform spectrometer

A multi-component Fourier Transform InfraRed (FTIR) gas analyzer with a low spectral resolution (8cm-1) is described in this paper. The hardware of this analyzer is consisting of a rugged Fourier Transform Spectrometer (FTS), an uncooled pyroelectric Deuterated L-Alanine TriGlycine Sulfate (DLATGS) detector, a glass body long-path gas cell and relevant sampling devices. The transplantable software and algorithms include the building of spectral library from the free sources such as EPA, NIST, HITRAN etc, identification of spectrum components and a modified classical least square regression with automatic baseline compensation. In order to validate this system, we implemented a continuous on-line experiment using the 55 μmol·mol-1 methane and 28 μmol·mol-1 nitrous oxide standard mixtures. The experimental results show this low resolution analyzer has accuracy and robust analysis abilities. The description in this paper is helpful to facilitate the development of a FTIR multi-component gas analyzer.