Laser Wavelength Measurement Research Articles

Asymmetric Etalon Effect in Fold-Type Optical Feedback Cavity-Enhanced Absorption Spectroscopy

To further improve the performance of cavity-enhanced spectroscopy systems, a high-quality U-cavity system was established. In the process of the experiment, an asymmetric ripple effect, which is different from the previous etalon effect, was found, which seriously affects the performance of the spectral system. This unique phenomenon mainly manifests in the different amplitudes of the fluctuations of the spectral curves measured by the folding mirror and the end mirror in the U-cavity system. Based on multi-beam interference theory, we analyzed the characteristics of the transmission spectrum of each mirror in the presence of the etalon effect at the end mirror, and obtained the following conclusions: for the U-cavity system, the strength of the etalon effect of each mirror is inversely proportional to its transmission loss value, that is, the larger the loss, the smaller the ripple of the transmission spectrum, and vice versa. In order to eliminate this effect, the most effective way is to eliminate the etalon effect caused by the light feedback of the end mirror. After improving the system, the minimum detectable absorption coefficient of αmin=8.33×10−9cm−1 is obtained with this U-shape Optical Feedback Cavity-Enhanced Absorption Spectroscopy. These works are valuable references for the design of folded Cavity-Enhanced Absorption Spectroscopy systems and have potential for laser wavelength calibration and measurement of a mirror’s reflectance.

Highly sensitive vibration measurement method of nanomechanical resonators using a convolutional neural network

Nanomechanical resonators can detect various small physical quantities. It is necessary to increase the sensitivity of nanomechanical resonators. In this study, a deep learning-based method is developed for sensitive detection of vibration states of nanomechanical resonators. It enables one to explore the most highly sensitive vibration states without missing targets while conventional methods focus only on the resonant frequency. The proposed method was evaluated with laser intensity. Sensitive measurement of laser intensity has the potential for applications in laser wavelength measurement. The proposed method could identify laser intensity at intervals of 0.03 mW at which the resonance frequency did not shift. Grad-CAM was used to clarify features on the vibration spectra used in the convolutional neural network. Frequency bands other than the resonance frequency band were used for the laser intensity measurement. This result implies that there is a possibility that highly sensitive vibration behavior exists outside the resonance frequency.

Wavelength calibration methods in laser wavelength measurement.

At present, accurate wavelength calibration plays an important role in laser spectrum measurements. Although the wavelength calibration methods have been investigated for a long time, there are no techniques that are particularly designed for laser spectral calibration to the best of our knowledge. A mathematical model for calibrating a pulse laser wavelength is first established, to the best of our knowledge. According to the analysis formula of dispersion aberration, a flat-field concave grating in the near-infrared band is designed. Then, a wavelength calibration model based on concave grating spectroscopy is proposed. Through adjusting the spectra of each pixel, we design a calibration algorithm based on the cubic spline interpolation and kernel regression methods. By compensating and interpolating spectral data, accurate wavelengths are obtained. Finally, some experiments verify the calibration performance of the proposed method. Meanwhile, the uncertainty of measurement is also analyzed.

Core-shell NaErF4@NaYF4 upconversion nanoparticles qualify as a NIR speckle wavemeter for a visible CCD.

Speckle patterns have been widely employed as a method for precisely determining the wavelength of monochromatic light. In order to achieve higher wavelength precision, a variety of optical diffusing waveguides have been investigated with a focus on their wavelength sensitivity. However, it has been a challenge to find a balance among the cost, compactness, precision, and stability of the waveguide. In this work, we designed a compact cylindrical random scattering waveguide (CRSW) as the light diffuser by mixing TiO2 particles and ultra-violate adhesive. In the CRSW, speckle patterns are generated by input light scattering off TiO2 particles multiple times. Additionally, a thin layer of upconversion nanoparticles (UCNPs) was sprayed on the end face of CRSW to allow near-infrared (NIR) light to be converted to visible light, breaking the imaging limitations of visible cameras in the NIR range. We, then, further designed a convolution neural network (CNN) to recognize the wavelength of the speckle patterns with excellent robustness and ability to transfer learning. This resulted in the achievement of a high wavelength precision of 20 kHz (∼0.16 fm) at around 1550 nm with a temperature resistance of ±2 °C. Our results demonstrate a low-cost, compact, and simple NIR wavemeter, which is capable of ultra-high wavelength precision and good temperature stability. It has significant value for applications in high-speed and high-precision laser wavelength measurements.

Femtometer-resolved simultaneous measurement of multiple laser wavelengths in a speckle wavemeter.

Many areas of optical science require an accurate measurement of optical spectra. Devices based on laser speckle promise compact wavelength measurement, with attometer-level sensitivity demonstrated for single wavelength laser fields. The measurement of multimode spectra using this approach would be attractive, yet this is currently limited to picometer resolution. Here, we present a method to improve the resolution and precision of speckle-based multi-wavelength measurements. We measure multiple wavelengths simultaneously, in a device comprising a single 1-m-long step-index multimode fiber and a fast camera. Independent wavelengths separated by as little as 1 fm are retrieved with 0.2 fm precision using principal component analysis. The method offers a viable way to measure sparse spectra containing multiple individual lines and may find application in the tracking of multiple lasers in fields such as quantum technologies and optical telecommunications.

Modified frequency-shifted interferometer: encoding wavelength into phase

We propose a novel modified frequency-shifted interferometer, where a Mach–Zehnder interferometer is added in order to obtain wavelength information. We use the Hilbert transform to extract the wavelength information from the phase of the interference pattern and construct the relationship between phase and wavelength. The laser wavelength measurement experiment is used to verify the compound interferometer. Experimental results demonstrated that our method could obtain the wavelength from the phase, which is of great significance for demodulation of the fiber Bragg grating based on a frequency-shifted interferometer.

Validation of vectorial theories for the focusing of high numerical aperture Fresnel zone plates

Abstract To study the applicability of vectorial angular spectrum (VAS) theory and vectorial Debye–Wolf diffraction integral for the focusing of high numerical aperture (NA) Fresnel Zone Plates (FZPs), these two vectorial methods have been rigorously examined by the three-dimensional finite-difference time-domain (FDTD) method under general and specific conditions. It is found that for a low total annulus number and when the wavelength dispersion or obstruction are existing, Debye–Wolf diffraction integral has failed to describe the light field distribution in the focal region. On the contrary, VAS theory can generally predict the focusing properties. However, when a FZP only contains one or two transparent annuli, both VAS and Debye–Wolf diffraction theories are invalid. Wavelength dispersion and purpose obstruction can produce the multi-focus or focal shift, which can be used for the axial wavelength scanning, the precise measurement of laser wavelength, or optical trapping.

Laser Wavelength Measurement Based on a Digital Micromirror Device

We constructed a relatively simple inexpensive wavemeter with completely static parts to measure the laser wavelength accurately based on diffraction from a Fresnel zone plate (FZP) displayed on a digital micromirror device. The unknown laser wavelength was measured by finding the proper FZP, focusing the laser beam exactly into the specified focal point. The relative uncertainty in the order of 10−5 was attained in He:Ne and second harmonic of Nd:YAG laser wavelength measurement.

Instant Laser Wavelength Measurement Based on Dual Fabry–Pérot Etalons

An all-fiber-instant laser wavelength measurement scheme based on dual etalons and an optical linear filter is proposed and demonstrated. The linear filter is utilized for the coarse measurement, while the Fabry–Perot etalons are employed for the fine measurement. By slightly tilting the refractive angle of one etalon, its phase and waveform can be tuned. Thus, the waveforms of two etalons can compensate for each other in measurements, covering the whole range without any dead zone. Various wavelength determination criteria are also discussed for different etalon phase offsets. Finally, a wavelength resolution of 1.38 pm is achieved within the whole $C$ -band (1520–1570 nm). The system exhibits many advantages, such as compact structure, low cost, and fast response.

Design of a New Microcontroller-Based Vernier Fringe Counter for Interferometric Measurement of Laser Wavelength

This paper presents a new electronic Vernier fringe counter for the wavelength measurement of a diode laser in a scanning interferometer. The system is intended to be a low cost alternative to commercial systems used for gauge block calibration. The counter stage and phase coincidence detector are made with a microcontroller and high-speed CMOS logic to achieve the required resolution. The microcontroller also can synchronize with other elements to make a fully automated measurement system. This electronic design improves the resolution of the electronic counters in the previous designs.

Development of a Laser Induced Fluorescence (LIF) system on thePlasma Material Interaction System (PLAMIS-II) device

A laser induced fluorescence (LIF) system has been developed for the plasma material interaction system (PLAMIS-II) device, which is equipped with a unique plasma gun composed of a LaB6 cathode and two anodes with electromagnets to generate a focused dense plasma. PLAMIS-II simulates the interactions of plasma with different materials and is to be used for the test of plasma facing components of fusion devices. The LIF system is composed of a seed laser with Littmann/Metcalf cavity and a master oscillator power amplifier to pump 3d4F7/2 metastable argon ion to 4p4D5/2 level at the wavelength of 668.61 nm, which has the following input parameters: laser power = 20 mW, line width < 100 kHz, and a mode-hop free tuning range > 70 GHz. For in-situ measurement of laser wavelength, the wavelength spectrum of an iodine cell was measured by a photo-transistor during LIF measurement. To measure argon ion temperature (Ti) and drift velocity (vd) in PLAMIS-II, the fluorescence light with the wavelength of 442.72 nm, emitted from 4p4D5/2 level to 4s4P3/2 level and passing through 1 nm band-width filter, was collected by the photomultiplier tube combined with a lock-in amplifier and a chopper with frequency of 3 kHz. Initial data of Ti and vd were analysed in terms of gas flow rate and applied power.

All Fiber Real-Time Laser Wavelength Measurement Method Based on Faraday Rotation Effect

An all fiber real-time laser wavelength measurement method based on Faraday rotation effect is proposed and demonstrated, for correcting the nonlinear tuning of wavelength sweep lasers. The wavelength measurement setup is mainly composed of a specially designed fiber magneto-optic device and a wavelength sensitive filter. When the linearly polarized lights with different wavelengths pass through the magneto-optic crystal, their polarization planes will be rotated at different angles. By taking use of the dispersion effect, the light wavelength can be measured by detecting the rotated angles. In our experiments, the wavelength resolution can reach 2.1 pm with a measurement range from 1520 to 1570 nm. Besides monitoring the wavelength tuning, it should be also useful in laser wavelength calibration and optical fiber sensing.

Computer-controlled high-precision Michelson wavemeter

The Michelson wavemeter is a popular instrument in many experiments where the high-precision measurement of a cw laser wavelength is required. In this paper, we describe a simple and inexpensive way to obtain high-precision measurements with this classical physicist’s tool. We exploit the time stamp provided by the high-frequency clock present in modern data acquisition cards to measure the fractional uncertainty of the interference signal. The resulting relative uncertainty value for our current set-up is of the order of 10−8 and can be potentially improved by a factor of 100.

Research on laser wavelength measurement with rotating Fabry–Perot mirror

A method using rotating Fabry–Perot (FP) mirror to measure CO2 laser wavelength was developed. The variation of FP transmittance changing with laser incident angle was calculated theoretically and the variation curve was given. The calculation illustrates that the variation of FP reflectance with incident angle 0 to 30 deg has little effect on the transmittance of FP. In the experiments, the CO2 laser transmittance variation of FP was measured at a wavelength of 9.27 μm. To improve the measurement precision of the laser wavelength, the method using the centrosymmetric peaks of FP transmittance curve in the range from −20 to +20 deg of laser incident angle was proposed. The precision of the measurement is about 0.01 μm. The experiment result is consistent with theoretical analysis, which demonstrates the feasibility of the laser wavelength measurement using rotating FP method.

Measurements of three-dimensional shape and sound-induced motion of the chinchilla tympanic membrane

Opto-electronic computer holographic measurements were made of the tympanic membrane (TM) in cadaveric chinchillas. Measurements with two laser wavelengths were used to compute the 3D-shape of the TM. Single laser wavelength measurements locked to eight distinct phases of a tonal stimulus were used to determine the magnitude and the relative phase of the surface displacements. These measurements were made at over 250,000 points on the TM surface. The measured motions contained spatial phase variations consistent with relatively low-order (large spatial frequency) modal motions and smaller magnitude higher-order (smaller spatial frequency) motions that appear to travel, but may also be explained by losses within the membrane. The measurement of shape and thin shell theory allowed us to separate the measured motions into those components orthogonal to the plane of the tympanic ring, and those components within the plane of the tympanic ring based on the 3D-shape. The predicted in-plane motion components are generally smaller than the out-of-plane perpendicular component of motion. Since the derivation of in-plane and out-of plane depended primarily on the membrane shape, the relative sizes of the predicted motion components did not vary with frequency.Summary: A new method for simultaneously measuring the shape and sound-induced motion of the tympanic membrane is utilized to estimate the 3D motion on the membrane surface.This article is part of a Special Issue entitled “MEMRO 2012”.

Laser wavelength measurement system based on optical wedge interference

Laser wavelength measurement system based on optical wedge interference

Laser wavelength measurement with fibre lambda meter

A new method for evaluating the ratio between a reference and an unknown wavelength is reported. A Young&apos;s interferometer with no moving parts is used. Light emerging successively from a known wavelength and an unknown wavelength is launched into an optical fibre; a resulting interference pattern is projected onto the sensor of a CCD camera. Data from more than 300 000 sensors are processed by spatial phase-stepping techniques. Finally the whole set of points is fitted to obtain the measured estimation.

13C2H2분자를 이용한 반도체 레이저 주파수 안정화 및 그 파장 측정

본 연구에서는 1550nm 영역에서 <TEX>$^{13}$</TEX>C<TEX>$_2$</TEX>H<TEX>$_2$</TEX>분자의 회전-진동 모드에 대한 분광을 수행하고, 각 전이선들에 대한 파장을 측정하였다. 파장 측정을 위해서 각 흡수선의 피크에서 레이저주파수 변조를 시켜, 변조신호의 1차 하모닉 록킹법으로 레이저의 주파수를 안정화시키고, 광주파수 표준기로 사용되고 있는 요오드 안정화 헬륨-네온 레이저(KRISS-R70l)로 교정한 파장계를 사용하여 3<TEX>$\times$</TEX><TEX>$10^{-7}$</TEX> 의 정확도로 <TEX>$^{13}$</TEX>C<TEX>$_2$</TEX>H<TEX>$_2$</TEX>의 전이선들의 파장을 측정하였다. 그리고, 아세틸렌 분자 흡수선의 옆선에 주파수 안정화하는 방법을 이용하여 ITU-T 그리드의 절대 파장에 일치하는 표준광원 개발은 제안하였다. We have measured the wavelengths of the absorption lines of the <TEX>$^{13}$</TEX> C<TEX>$_2$</TEX>H<TEX>$_2$</TEX>molecule by using a wavelength meter calibrated against the national optical frequency standard (iodine Stabilized He-Ne Laser, KRISS-R701) in the visible wavelength region. To measure the absolute wavelengths of the absorption lines, the frequency of the laser has been stabilized in the peaks and the sides of the absorption lines of <TEX>$^{13}$</TEX> C<TEX>$_2$</TEX>H<TEX>$_2$</TEX>. Also, we have proposed the development of a frequency standard source of ITU-T grid using stabilization in the sides of the absorption lines of <TEX>$^{13}$</TEX> C<TEX>$_2$</TEX>H<TEX>$_2$</TEX>.

Highly accurate method for single-mode fiber laser wavelength measurement

We propose a simple technique by which the wavelength of a single-mode fiber laser can be easily measured to accuracy of the order of 1 pm. The technique is based on the wavelength dependence of polarization mode beating frequencies. Direct application of this method for wavelength stabilization of fiber lasers and the possibility of obtaining information about the polarization mode dispersion of the fiber used within the laser cavity are discussed.

A reliable, compact, and low-cost Michelson wavemeter for laser wavelength measurement

We describe the construction and operation of a simple, compact, and cost effective Michelson wavemeter with picometer accuracy. The low cost of the device means that it can form the basis of an undergraduate laboratory experiment, yet it is sufficiently reliable and accurate that it has become an important tool in our research laboratory, where it is regularly used to tune lasers to atomic transitions. The usefulness and accuracy of the wavemeter is demonstrated by tuning two separate extended cavity diode lasers to achieve two-step excitation of the Rb 52D state, observed by detecting 420 nm blue fluorescence from the 52D→62P→52S decay path.