Direct frequency comb optical frequency standard based on two-photon transitions of thermal atoms

High-resolution Cs-Rb two-photon spectrometer for directly stabilizing a Ti:sapphire comb laser

In this paper, we present a simple scheme for efficiently removing the residual Doppler background of a comb laser based two-photon spectrometer to be better than 10^-3 background-to-signal ratio. We applied this scheme to stabilize the frequencies of a mode-locked Ti:sapphire laser directly referring to the cesium 6S-8S transition and rubidium 5S-5D transition. We suggest a standard operation procedure (SOP) for the fully direct comb laser stabilization and evaluate the frequency of two spectral lines at a certain temperature, by which we demonstrate an all-atomic-transition-based Ti:sapphire comb laser merely via a 6-cm glass cell.

Direct Kerr frequency comb atomic spectroscopy and stabilization

Microresonator-based soliton frequency combs, microcombs, have recently emerged to offer low-noise, photonic-chip sources for applications, spanning from timekeeping to optical-frequency synthesis and ranging. Broad optical bandwidth, brightness, coherence, and frequency stability have made frequency combs important to directly probe atoms and molecules, especially in trace gas detection, multiphoton light-atom interactions, and spectroscopy in the extreme ultraviolet. Here, we explore direct microcomb atomic spectroscopy, using a cascaded, two-photon 1529-nm atomic transition in a rubidium micromachined cell. Fine and simultaneous repetition rate and carrier-envelope offset frequency control of the soliton enables direct sub-Doppler and hyperfine spectroscopy. Moreover, the entire set of microcomb modes are stabilized to this atomic transition, yielding absolute optical-frequency fluctuations at the kilohertz level over a few seconds and <1-MHz day-to-day accuracy. Our work demonstrates direct atomic spectroscopy with Kerr microcombs and provides an atomic-stabilized microcomb laser source, operating across the telecom band for sensing, dimensional metrology, and communication.

A Deep Ultraviolet Mode-locked Laser Based on a Neural Network

Deep ultraviolet lasers based on the phenomenon of mode-locking have been used widely in many areas in recent years, for example, in semiconductors, the environment and biomedicine. In the development of a mode-locked deep ultraviolet laser, one of the most important aspects is to optimize the multiple parameters of the complex system. Traditional optimization methods require experimenters with more optimization experience, which limits the wide application of the lasers. In this study, we optimize the deep ultraviolet mode-locked laser system using an online neural network to solve this problem. The neural network helps us control the position of the crystal, the length of the cavity, the position of the focusing lens and the temperature of the frequency doubling crystal. We generate a deep ultraviolet mode-locked laser with a power of 18 mW and a spectral center at 205 nm. This result is greatly improved compared to previous results with the same pump power. This technology provides a universal solution to multiparameter problems in the optimization of lasers.

Precise and highly-sensitive Doppler-free two-photon absorption dual-comb spectroscopy using pulse shaping and coherent averaging for fluorescence signal detection

We demonstrated Doppler-free two-photon absorption dual-comb spectroscopy of 5S_1/2 - 5D_5/2 and 5D_3/2 transitions of Rb. We employed simple pulse-shaping of the dual-comb source and eliminated Doppler-broadening backgrounds, which cause fitting errors of the Doppler-free signals. Moreover, to improve sensitivity, we investigated the coherence in dual-comb fluorescence signals and the coherent averaging method was applied to fluorescence dual-comb detection for the first time. The detection sensitivity was significantly improved by coherent averaging to reduce the noise floor. Observed Doppler-free spectra was fitted to Voigt profiles and we performed absolute frequency determination with a precision of about 100 kHz.

Doppler-free dual-comb spectroscopy of Rb using optical-optical double resonance technique

We present a Doppler-free high-resolution dual-comb spectroscopy technique in which a dual-comb system is employed to perform optical-optical double-resonance (OODR) spectroscopy. In our experimental study, Doppler-free high-resolution and high-frequency-accuracy broadband measurements were realized using the proposed OODR dual-comb spectroscopic technique, which does not require high-power-per-mode frequency combs. We observed fully resolved hyperfine spectra of 5P_3/2 - 4D_5/2, 4D_3/2 transitions of Rb at 1530 nm and precisely determined the absolute frequencies of the transitions, with an uncertainty of less than 1 MHz. The variations of the OODR spectral line shapes due to power broadening and alignment and the effects of polarization on the dual-comb OODR spectra were also analyzed. This study provides a widely applicable technique for Doppler-free dual-comb spectroscopy of various gaseous species.

A pH-responsive poly(ether amine) micelle with hollow structure for controllable drug release

A pH-responsive poly(ether amine) micelle with hollow structure was developed for controllable drug release.