Absolute distance measurement of rough surfaces using asynchronous optical sampling

Correlation between the presence of dislocations and vacancies in N-Type gallium arsenide : E. Fabre and C. Schiller. Solid State Commun.10 (1972), p. 81

In this contribution, we demonstrate a free-running bidirectional Er-doped fiber dual-comb source based on asymmetric nonlinear polarization rotation (NPR) mode-locking, which for the first time realizes the repetition frequency difference (Δ<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$f_\text{rep}$</tex-math></inline-formula>) at the KHz level in directional-multiplexed Er-doped fiber dual-comb sources with fully shared cavity to the best of our knowledge. The standard deviation <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sigma$</tex-math></inline-formula> of the Δ<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$f_\text{rep}$</tex-math></inline-formula> is only 0.7 Hz over 20 min in the absence of temperature control and vibration isolation. Further, the relative timing jitter of this dual-comb pulse is simulated and characterized by asynchronous optical sampling. A visual analysis of the period jitter using eye diagrams shows a period timing jitter of 1.91 fs for the dual combs in the quantum limit. Our work provides a bidirectional NPR single-cavity dual combs, which can be used as a laser source for applications such as spectroscopy, optical sensing, and absolute distance measurement.

Absolute distance measurement based on the dual-comb system is a promising tool for the large-scale measurement in the industrial field. There are two combs with slightly different repetition rates in the dual-comb system, and the distance information could be obtained by the asynchronous optical sampling (ASOPS). However, the measured range could be limited within the pulse-to-pulse interval range by the non-ambiguity range (NAR) without the extension. This paper proposes a method to extend the unambiguous range by changing the repetition range. Firstly, the method of dual-comb ranging and the principle of extending the non-ambiguity range were introduced. Secondly, the two implementations of changing single repetition frequency and switching repetition frequency were compared through simulation. Then, according to the simulated results, the effective conditions and theoretical maximum range of extended ranging were clarified. Finally, a long absolute distance measurement was designed and the ranging results of switching repetition frequency were compared with the conventional incremental interferometer, which proves that this method is reliable for extending the non-ambiguous range.

To promote underwater construction, the tools such as underwater robotic manipulator system, underwater vehicles and so on are necessary. Furthermore, these system need an accurate 3D position parameters. If no position information for automatic control system that system is difficult to be operated. Hence, it is important to take position information. Although 3D position camera can offer 3D position parameters, it has still some deviation. In addition, the manipulator system need accurate distance information for fast and accurate operation. Hence, an accurate distance measurement system is necessary for a remotely teleoperated robotic manipulator system for underwater constructions. This paper focus on the distance measurement study to offer a accurate target distance information. The information can combine with 3D position camera to obtain more accurate 3D position parameters to offer a useful position information for underwater constructions, with a remotely teleoperated robotic manipulator system. In this paper, three distance measurement system, includes commercial ultrasonic distance measurement system, fabricated ultrasonic system and a laser distance measurement system is study. The commercial distance measurement system have a distance measurement system rang 8~35 cm, plusmn0.1 cm. However, a short distance measurement is difficult to be measured with the measurement system. On the other side, the fabricated measurement system can measure a short distance. Information from 0~5 cm, accuracy plusmn0.3 cm. The fabricated distance measurement system fabricated with PZT thin film. In this study, a horn is added to improve the accuracy of distance measurement. In addition, the laser distance measurement system, measurement system is used to measure the distance information also in this study. The combination of these distance measurement system to form a multiple range distance measurement can offer a long measurement range for accurate distance measurement underwater. A detailed experiment is to be studied in the future. Furthermore, the distance measurement system has been offered a distance measurement in a remotely teleoperated robotic manipulator system for underwater constructions

A compact femtosecond dual-oscillator pump-probe setup with 48 MHz-repetition rate, relying on asynchronous optical sampling, is presented. The relative timing jitter between both lasers over the whole pump-probe delay range is of the order of or lower than 500 fs. We demonstrate that both a picosecond temporal resolution and a 48 MHz spectral resolution combined with the fast acquisition rate inherent to the asynchronous optical sampling allow performing broadband opto-acoustic imaging with a spectrum covering more than two decades from 300 MHz to 150 GHz. As an illustration, the opto-acoustic response of a supported thin film is investigated, revealing high frequency acoustic echoes close to the epicenter as well as low GHz surface acoustic waves propagating up to 40μm away from the epicenter. Semi-analytical calculations have been carried out and perfectly reproduce the dispersion of the surface acoustic waves experimentally observed.

We present the design and capabilities of a high-resolution, decade-spanning ASynchronous OPtical Sampling (ASOPS)-based TeraHertz Time-Domain Spectroscopy (THz-TDS) instrument. Our system employs dual mode-locked femtosecond Ti:Sapphire oscillators with repetition rates offset locked at 100 Hz via a Phase-Locked Loop (PLL) operating at the 60th harmonic of the ∼80 MHz oscillator repetition rates. The respective time delays of the individual laser pulses are scanned across a 12.5 ns window in a laboratory scan time of 10 ms, supporting a time delay resolution as fine as 15.6 fs. The repetition rate of the pump oscillator is synchronized to a Rb frequency standard via a PLL operating at the 12th harmonic of the oscillator repetition rate, achieving milliHertz (mHz) stability. We characterize the timing jitter of the system using an air-spaced etalon, an optical cross correlator, and the phase noise spectrum of the PLL. Spectroscopic applications of ASOPS-THz-TDS are demonstrated by measuring water vapor absorption lines from 0.55 to 3.35 THz and acetonitrile absorption lines from 0.13 to 1.39 THz in a short pathlength gas cell. With 70 min of data acquisition, a 50 dB signal-to-noise ratio is achieved. The achieved root-mean-square deviation is 14.6 MHz, with a mean deviation of 11.6 MHz, for the measured water line center frequencies as compared to the JPL molecular spectroscopy database. Further, with the same instrument and data acquisition hardware, we use the ability to control the repetition rate of the pump oscillator to enable THz frequency comb spectroscopy (THz-FCS). Here, a frequency comb with a tooth width of 5 MHz is generated and used to fully resolve the pure rotational spectrum of acetonitrile with Doppler-limited precision. The oscillator repetition rate stability achieved by our PLL lock circuits enables sub-MHz tooth width generation, if desired. This instrument provides unprecedented decade-spanning, tunable resolution, from 80 MHz down to sub-MHz, and heralds a new generation of gas-phase spectroscopic tools in the THz region.

We demonstrate a new method for pump-probe spectroscopy by applying arbitrary detuning asynchronous optical sampling (AD-ASOPS) to two independent amplified laser systems. The resulting time dynamics ranges from 400 fs up to 1 ms.

Asynchronous optical sampling using two slightly detuned GHz-repetition rate femtosecond lasers is employed to spectrally characterize integrated THz resonators for biomolecular sensing. Temporal delay scanning at kilohertz frequencies paves the way for high-throughput analytics.

When using diamond tool to cut the special stainless steel, the influence of cutting parameters on machining surface roughness is so great. Experiments of cutting special stainless steel by ultrasonic vibration were taken to develop the law that cutting parameters influence on surface roughness of the work piece. The relation curves between cutting parameters and the work piece surface roughness were achieved by contrast experiments with different cutting speed, tool feeds, cutting depth and vibration parameters. The result shows that cutting parameters have an obvious effect on surface roughness. Under given Conditions, the smaller amplitude of the vibration, the worse the surface roughness, and the higher vibrating frequency, the better surface roughness, and the more cutting depth and feeds, the worse surface roughness. Among these parameters, tool feeds was main effect on the surface roughness.

The traditional contact devices measure material's surface roughness by scratching its surface, which may cause surface damage and sampling error. In order to avoid these troubles, an optical measurement system is used in this paper. Considering the anisotropic and inhomogeneous surface structure of Cf/SiC composite, a multi-scale measure system must be established. Fiber bundle is the first scale to be studied, whose appropriate measurement parameters are studied here. When sampling area is 150μm×150μm and sampling step is from 0.1μm to 0.5μm, the values of 3D surface parameters Sa, Sq, Ssk and Sku are steady and their relative changes are small. 2D surface roughness Ra is adopted to select the proper sampling length. The results show that as long as the sampling length is more than 112μm, the mean value of 2D surface roughness Ra are relatively stable. The critical sampling length is about 1/7 of the standard minimum sampling length in ISO 468-1982. According to the results obtained, the research provides a useful guideline for determination on the appropriate sampling conditions of Cf/SiC composite fiber bundle surface measurement.

Zirconium carbon nitride (ZrCN) hard films own lower friction coefficient, high hardness, higher wear and corrosion resistance. A low-cost optical inspection system for rapid surface roughness measurements of ZrCN hard films is developed in this study. The savings in modulation time of photodetector for a new measurement angle is up to 60%. The incident angle of 20° is found to be a good candidate for predicting the surface roughness of ZrCN hard films. Surface roughness of ZrCN hard films can be determined rapidly from the average value of the reflected direct current voltage recorded by the optical system developed. The maximum measurement error rate of the optical measurement system developed is less than 12.37%.

In this letter, we develop a compact and all-fiber system for absolute distance measurement using self-heterodyne electro-optic (EO) comb interferometry. The repetition frequency is at the level of hundreds of MHz, $\ll$ tens of GHz (typical value of EO comb), and the non-ambiguity range is large. The individual comb mode can be resolved by the self-heterodyne interferometry, and the phases of the resulting beat notes can be used to measure the distances. Compared with the reference distance meter, the experimental results show an agreement within $4~\mu \text{m}$ in 50 m range, corresponding to $8\times 10^{-8}$ in relative.

Measurement systems for metrology incorporating laser-triangulation methods have the problem of speckle noise. This noise is an effect of the coherence of the laser light in combination with the projection onto rough object surfaces. In this contribution, we show results for using spatial light modulators within a simple and effective method in order to reduce the speckle noise in laser-based triangulation. In the last decades, spatial light modulators have been intensively used for different applications in optical measurement systems. Today, the elements have high enough resolutions to be used even for simple holographic applications. We generate dynamic holograms with a pixelated spatial light modulator by inscribing multiple holograms. The laser-illuminated holograms microscopically translate the measuring point in the object plane. Due to the minimal different spot positions, the speckle patterns are also subject of change. By averaging of the intensity field in the camera plane the speckle noise can be reduced and the accuracy of the spot's position measurement is increased. Furthermore, experimental measurements show features of correcting spot deformations due to optical system aberrations like defocus, astigmatism and coma.

An overview of recent advances in measurement modalities using dual femtosecond laser configurations such as asynchronous optical sampling and frequency comb spectrometry is provided. These enable time-resolved interactions of light with matter across different parts of the electromagnetic spectrum. An enhanced energy exchange and thus signal-to-noise-ratio between a sensing system and its local environment is possible through the use of resonant structures, metamaterials, plasmonics, dielectric microspheres and other slow-light structures. Finally, new ways of interpreting measurements of relevance to nanotechnology using state space network analysis, system identification and dielectrics theory are discussed using examples from atomic force microscopy, memristive systems and nanosquids (superconducting quantum interference devices).

Terahertz (THz) waves are valuable for evaluating non-metallic materials due to their strong penetrative capabilities. Conventional THz time-domain spectroscopy (THz-TDS) systems based on asynchronous optical sampling (ASOPS) use ultrashort pulse lasers however require a mechanical delay stage, resulting in a trade-off between spectral resolution and acquisition time. Dual-comb spectroscopy (DCS) eliminates the need for delay stage, enabling broadband, high-resolution, and rapid measurements [1], and has been applied to ASOPS THz-TDS systems [2]. However, conventional DCS systems are typically large and complex, as they require precise stabilization of two independent lasers.