We present an alternative scheme for determining the frequencies of cesium (Cs) atom 6S-8S Doppler-free transitions. With the use of a single electro-optical crystal, we simultaneously narrow the laser linewidth, lock the laser frequency, and resolve a narrow spectrum point by point. The error budget for this scheme is presented, and we prove that the transition frequency obtained from the Cs cell at room temperature and with one-layer μ-metal shielding is already very near that for the condition of zero collision and zero magnetic field. We point out that a sophisticated linewidth measurement could be a good guidance for choosing a . Two research groups have tried to obtain the transition frequencies by very different approaches [1,7], namely, "direct comb laser spectroscopy" and "frequency chain." We here demonstrate a third approach for obtaining new frequencies of the two Dopplerfree 6S-8S transitions with 1 order of magnitude higher precision over the latest published measurement [1]. The accuracy of the transition frequency is discussed after we have inspected ten Cs cells. We suggest the frequency to be determined from the cells that yield the Lorentian-part linewidth near the theoretical natural linewidth. Figure 1 shows a simplified block diagram of our experimental design, which allowed us to simultaneously achieved the following three primary tasks of narrowing the laser linewidth, stabilizing the laser frequency, and scanning the laser carrier frequency for high-precision spectroscopy. The extended cavity diode laser (ECDL) system (Fig. 1) served as the master laser [5] in this experiment. The output light after a tapered amplifier (TA) was sent to a spatial filter, and then a 200 mW spatially regulated laser beam was split equally into the electro-optical modulator (EOM) area and acoustic-optical modulator (AOM) area in which the time base of the two modulator's drivers were all phase locked against the time base of a Cs clock. The EOM area is set up for both laser stabilization and laser carrier frequency (ω c ) scanning. The driving frequency of the EOM is provided by a function generator (Agilent 81150A) that allows us to dither the EOM modulation frequency (Δ 0 ) with an external dither source (ω d , Agilent 33250A). Consequently, the optical phase (ϕ) was modulated as ϕ M cos Δt with a dither frequency ω d embedded in the modulation frequency Δ, that is, Δ Δ 0 A cos ω d t.Here, a modulation index (MI) of 0.4 rad is used; Δ 0 is 106 MHz; A is 1 MHz; ω d is 28 kHz. Dithering the EOM frequency was for obtaining a first-derivative spectrum from Cs cell #1 (81°C wall temperature). The smooth curve on the center of the Pound-Drever-Hall (PDH) signal (green dashed inset, Fig. 1), for reducing laser jitter to 20 kHz bandwidth, proves an interesting fact that the aforementioned dither on sidebands was just canceled out in the heterodyned PDH signal. That is, dither Fig. 1. Simplified block diagram for simultaneously narrowing laser linewidth, stabilizing laser carrier frequency by cell #1, and resolvin...

Glass-cell–based secondary clocks, including coherent population trapping (CPT) clocks, are the most used clocks in modern laboratories and in industry. However, the reported frequency accuracies of those secondary clocks were always much worse than expected, though all error sources have been previously discussed. In this report, a high-precision measurement on the spectral frequency-linewidth relation (FL-R) is first used for revealing a new error source in secondary clocks by which we answer the puzzle raised in Opt. Lett. 38, 3186 (2013)10.1364/OL.38.003186.

A dual-comb laser system containing two femtosecond Ti:sapphire (Ti:S) lasers is reported, in which the ultrashort pulses are pumped by one common fiber laser and the influences of the different pumping noise are presented both in time-domain and frequency-domain. In addition, the dimensions of dual Ti:S comb system are reduced due to the implementation of one hand-sized optical frequency reference, from which the needed space and cost for two ''self-reference'' optics are saved.