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Nonlinear optical (NLO) crystals can be employed to expand the laser frequency and thus are of technical importance in advanced laser science. Noncentrosymmetric rare earth compounds keep attracting broad interest as a significant branch of NLO materials because the highly distorted structural motifs centered by rare earth ions could remarkably benefit the second harmonic generation. In this review, we proceed from structure–properties relationship and reveal the role of rare earth element in the optical properties of NLO materials. We believe that this work can deepen the understanding of rare earth-based NLO materials and provide some enlightenment for exploring novel practical NLO crystals.

Laser frequency stabilization is one of the key technologies in atomic physics experimental system. In this paper, the basic principles, and features and the latest research progress on various kinds of semiconductor laser, active frequency stabilization techniques based on different locking reference standards are systematically described, and their practical applications in different fields are briefly overviewed. Finally, we provide a prospective development trends for semiconductor laser, active frequency stabilization technologies.

With the advantages of high resolution, high sensitivity, wide spectral coverage and rapid measurement, the dual-comb spectroscopy technology has developed rapidly in the field of molecular and atomic spectroscopy. According to the principle of dual-comb spectroscopy and taken the number of pump light sources used as the classification criteria, the principles of multiple dual-comb spectroscopy techniques are briefly introduced basen on different implementation schemes at home and abroad in recent years, the various experimental schemes were described proposed by different experimental groups with different numbers of pump light sources, and the results of their spectral experiments were introduced. With the deepening of research, reducing the number of pump light sources used is one of the important directions for the development of dual-comb spectrometers to achieve miniaturization of equipment, and the increase is an important development idea from one-dimensional to multi-dimensional. The classic dual light source configuration has made important progress in accuracy and two-dimensionalization.

We experimentally observed a depression in the laser-induced cesium beam fluorescence spectrum. This paper describes the optical configuration we realized and proves that the hole can be used for laser frequency stabilization. The spectrum was recorded under different conditions. We theoretically analyzed the physical origin of this effect and found that the hole could have a sub-natural line width. This indicates that it could have great application prospects in atomic experiments and beam-type quantum precision instruments due to the simple construction.

We have analyzed the characteristic features and problems in the major approaches to measurement of laser frequency noise. We propose a method in which we use an unbalanced fiber-optic interferometer, generation at the optical system output of a signal for a subcarrier of the frequency, phase-modulated by fluctuations in the laser frequency, and measurement of the spectrum for this signal. The proposed approach is distinguished by relative simplicity and accessibility, and does not require using uncommon specialized instruments and complicated specific procedures.

Optical frequency combs play a crucial role supporting optical frequency standards and cover a wide range of wavelengths (octaves). However, broadening the comb spectrum to the short-wavelength visible region (λ

An absolute distance measurement system based on LFSI with an auxiliary interferometer for nonlinearity correction is established. The tunable wavelength range of the laser source is between 1528nm and1568nm. The experimental results shows that the error is within 13μm in the measuring range of 1-10mm. It is found that the distance varies over time with the speed up to 15nm in one scan cycle of laser source, which has not been mentioned in the previous research. In order to solve this problem, the drift of the distance is analyzed, which can guide us to improve the precision of Laser Frequency scanning interferometry method.

The influence of the laser frequency drift on the operation of phase-sensitive optical time-domain reflectometry ($\Phi$-OTDR) systems is considered. Theoretical results based on a new numerical $\Phi$-OTDR model demonstrating the influence of the laser frequency instability on a signal are reported. This model is verified based on experimental data. It has been used to calculate the signal-to-noise ratio (SNR) of the system for different parameters of the laser source stability. As a result, quantitative requirements for lasers used in $\Phi$-OTDR systems are formulated., Comment: 8 pages, 7 figure

The mid/far-infrared (MFIR) nonlinear optical (NLO) materials are very important for the development of new laser sources through laser frequency conversion technologies. In this work, two new noncentrosymmetric chalcogenide compounds Ba10In6Zn7S10Se16 (S10Se16) and Ba10In6Zn7Se26 (Se26) were successfully synthesized for MFIR NLO materials. They are composed of T2 super tetrahedron and show excellent comprehensive NLO performance. Their NLO coefficients are approximately 0.7 and 0.8 times of AgGaS2 at 2.05 μm, and both have high laser induced damage threshold (LIDT) about 12.3 and 10.0 times of AgGaS2, respectively. Both compounds show consistent melting characteristics, which is beneficial for the growth of large-size crystals. The band gaps, NLO coefficients, and density of states (DOS) of the crystals are calculated by first principles simulations to study the origination of NLO response, which indicates that the NLO performance of Se26 is mainly derived from tetrahedrons and supertetrahedrons composed of In/Zn and Se.

New methods for growing LiIO3 and Ba(NO3)2 crystals have been developed. Barium nitrate crystals up to 12 × 12 × 100 mm3 in size and lithium iodate crystals up to 120 × 120 × 200 mm3 in size of necessary optical quality are obtained. The influence of рН on the morphology of Ba(NO3)2 growth faces is investigated. The data on the morphology of the {111} and {$$\bar {1}\bar {1}\bar {1}$$} faces of crystals grown at different solution acidities are obtained by atomic force scanning microscopy. The possibility of fabricating optical elements from LiIO3 crystals of ~100 × 100 × 100 mm3 in size is shown.

By using the Mie theory, nonlinear absorption coefficient and electromagnetically induced transparency (EIT) of a hybrid system consisting of GaAs spherical quantum dot (SQD) with ladder model and parabolic potential in the vicinity of a spherical metal nanoparticle (SMNP) are investigated. The density matrix equations in steady-state are solved and the third order susceptibility is obtained. Then, by using imaginary part of third order susceptibility, the nonlinear absorption coefficient are computed. Then, the effects of radii of SQD and SMNP, distance between SQD and SMNP and control laser frequency on nonlinear absorption coefficient and electromagnetically induced transparency (EIT) are investigated.

Microchip resonator Nd:YVO 4 /YVO 4 /KTP/Er:Glass with second-harmonic generation and relative frequency stabilization to 127I 2 iodine vapor atomic transition is presented. Auxiliary 976nm beam is absorbed in Er:Glass leading to the laser frequency control induced by photothermal effect.

We report on an ongoing development of a compact and transportable iodine frequency stabilized laser setup, based on compact and fibered Telecom components with a high technological readiness level (TRL). This laser system is being planned as a compact and easily transportable ultra-stable frequency reference for ground tests of the payload of LISA mission (Laser Interferometer Space Antenna) as part of the SYRTE laboratory contribution to the French activities carried out by a consortium of several partners lead by the French Space Agency (CNES) for assembly-integration and tests (AIVT) of the payload of LISA. This frequency reference will match the LISA requirements in terms of both residual frequency and intensity noise. The target residual frequency noise for this stabilized laser is below the nominal requirement for LISA, which is currently 30 Hz/ Hz. Thus, we propose to provide a tandem of 1064 nm laser sources phase-locked to an iodine stabilized Telecom laser operating at 1596 nm. The frequency gap between the telecom domain and the green range is bridged using a frequency tripling process based on two cascaded PPLN crystals, fully fibered. The compact design of the whole setup will make it easily transportable to different sites and could be readily used for ground tests of the LISA payload.

Ultra-low frequency noise lasers have been widely used in laser-based experiments. Most narrow-linewidth lasers are implemented by actively suppressing their frequency noise through a frequency noise servo loop (FNSL). The loop bandwidths (LBW) of FNSLs are currently below megahertz, which is gradually tricky to meet application requirements, especially for wideband quantum sensing experiments. This article has experimentally implemented an FNSL with loop-delay-limited 3.5 MHz LBW, which is an order higher than the usual FNSLs. Using this FNSL, we achieved 70 dB laser frequency noise suppression over 100 kHz Fourier frequency range. This technology has broad applications in vast fields where wideband laser frequency noise suppression is inevitable.

The back-surface field (BSF) layer obtained through the laser fired contact (LFC) process is the key to increasing the efficiency of solar cells. In this paper, we studied the optimization of LFC process parameters—focusing on laser frequency, influence, and speed—to achieve good ohmic contacts, and to reduce the heat-affected zone (HAZ). As frequency increases, interactions between the laser and particles increase, with the particles becoming overly heated. This generates the thermal effect, in which heat is transferred to particles not directly affected by the laser—resulting in the HAZ becoming wider and deeper. Under different laser power conditions, depths of approximately 18 and 8.3 μm were observed at laser speeds of 10 and 100 mm/s, respectively. This analysis of performance variables allowed us to identify those best suited to forming an Al-BSF layer approximately 1.2 μm thick, which resulted in the best LFC procedure while minimizing the HAZ area. HAZ size was minimized at a frequency of 400 kHz, using 5 W laser power, and a laser speed of 100 mm/s, while the best cell characteristics were obtained using a laser pitch of 500 μm and a single laser process.

Infrared (IR) nonlinear optical (NLO) materials are the key devices for generating tunable infrared output between ∼3 and ∼20 μm by laser frequency conversion techniques. Based on the study of structure and properties, chalcogenides, pnictides and oxides, have been demonstrated as the most promising systems for the exploration of new IR NLO materials with excellent optical performances. Over the past decades, many state-of-the-art IR NLO materials have been discovered in these systems. In this work, the synthesis, characterization and performance of the new developed promising IR NLO materials are summarized and analyzed. The typical IR NLO materials with large-size single crystals are selected as the representatives for the detailed discussions. Moreover, the discrepancies in optical properties of single crystal, polycrystalline powders, and the corresponding calculated results are discussed, aiming to provide suggestions for the exploration of next generation IR NLO material in these systems.

We propose a machine learning based scheme to estimate transmitter laser frequency offset, which is a nonnegligible factor affecting the performance of transceiver-joint equalization. The estimation error is less than 0.05 GHz.

We propose a method for slowing, cooling and trapping Yb atoms using stimulated forces and only the 1S0 → 3P1 transition. With laser frequency chirp, our computer simulation predicts a MOT loading rate over 108 atoms/s.

We present an electro-optic technique that generates an independent readout of optical cavity mode frequency spacing. We demonstrate a fractional frequency drift resolution of 1 ppb, sufficient to meet expected future mass change mission requirements.