Haosen Shang

Hollow cathode lamp based Faraday anomalous dispersion optical filter

The Faraday anomalous dispersion optical filter (FADOF), which has acquired wide applications, is mainly limited to some gaseous elements and low melting-point metals before, for the restriction of the attainable atomic density. In conventional FADOF systems a high atomic density is usually achieved by thermal equilibrium at the saturated vapor pressure, hence for elements with high melting-points a high temperature is required. To avoid this restriction, we propose a scheme of FADOF based on the hollow cathode lamp (HCL), instead of atomic vapor cells. Experimental results in strontium atoms verified this scheme, where a transmission peak corresponding to the 88Sr (5s2)1S0 − (5s5p)1P1 transition (461 nm) is obtained, with a maximum transmittance of 62.5% and a bandwith of 1.19 GHz. The dependence of transmission on magnetic field and HCL discharge current is also studied. Since the state-of-art commercial HCLs cover about 70 elements, this scheme can greatly expand the applications of FADOFs, and the abundant atomic transitions they provide bring the HCL based FADOFs potential applications for frequency stabilization.

A transportable calcium atomic beam optical clock

Achievement on atomic optical clock, which has reached to 10-18 level uncertainty, accelerates the research of the fundamental physics. But enormous volume size limits the application of optical clock outside the lab. Here, we report a transportable Calcium atomic beam optical clock with higher stability than general microwave clocks. In this system, we use the electron-shelving method to greatly improve the signal-to-noise of 657 nm signal. After locking, the stability of transportable Calcium atomic beam optical clock is 3.0 × 10-14 at 1 s and decreases to 2.9 × 10-15 at 200 s with continuous working time 11000 s by self-evaluation. Then we have used a 750 MHz repetition frequency optical frequency comb to transfer Calcium atomic beam optical clock frequency to microwave and compare with Hydrogen maser. The frequency stability of Calcium atomic beam optical clock versus hydrogen maser reaches to 1.62 × 10-12 at 1 s, which is close to the frequency stability of Hydrogen maser. The whole system is specially designed for robustness. Besides, a new full-sealed Calcium atomic beam vacuum system without flanges is constructed.

Experimental study of a miniaturized calcium atomic beam tube for small optical frequency standard

With the advantage of relatively simple structure, the optical frequency standard based on calcium thermal atomic beam has the potential to be miniaturized and engineered. We develop a new fully vacuum-sealed calcium atomic beam tube, which divergence angle of calcium atomic beam is narrower and background noise of 423 nm laser-induced fluorescence is much lower than its predecessor. This paper describes experimental study of this new tube using the 657 nm clock transition laser and 423 nm detection laser.

A highly integrated single-mode 1064 nm laser with 8.5 kHz linewidth for dual-wavelength active optical clock

Without exploiting any frequency selective elements, we have realized a highly integrated, single-mode, narrow-linewidth Nd:YAG 1064 nm laser, which is end-pumped by the 808.6 nm diode laser in an integrated invar cavity. It turns out that each 1064 nm laser achieves a most probable linewidth of 8.5 kHz by beating between two identical laser systems. The output power of the 1064 nm laser increases steadily as the 808.6 nm pump power is raised, which can be up to 350 mW. Moreover, the resonant wavelength of cavity grows continuously in a certain crystal temperature range. Such a 1064 nm laser will be frequency stabilized to an ultrastable cavity by using the Pound-Drever-Hall technique and used as the good cavity laser to lock the main cavity length of 1064/1470 nm good-bad cavity dual-wavelength active optical clock.

Frequency stabilization of 423 nm laser for calcium-beam optical frequency standard

The Ca beam optical frequency standard has the potential to be small optical clock like small Cs beam clock in microwave regime. For improving the signal-to-noise ratio of the clock transition spectroscopy, the electron shelving detection, which uses the fast ¹S<inf>0</inf>-¹P<inf>1</inf> 423nm transition to detect the narrow ¹S<inf>0</inf>-³P<inf>1</inf> 657nm clock transition, was applied for Ca beam optical frequency standard. Therefore the frequency stability of 423 nm laser to some extent determines the performance of the optical frequency standard. In this paper, we stabilize the 423 nm laser frequency to Ca beam signal with side-band locking technique and estimate the preliminary stability of 423 nm laser which is 1.4×10⁻¹¹ at 1 s and 2×10⁻¹² at 100 s.

Precision measurement of the hyperfine structure of the 85Rb 6P 3/2 state

Partly subjected to the stability of optical frequency source, the magnetic dipole and electric quadrupole hyperfine constants of the ⁸⁵Rb 6P<inf>3/2</inf> State have been reported to be 8.163(4) MHz and 8.191(27) MHz, respectively. To pursue the higher precision, here we have constructed two more robust ⁸⁵Rb spectrometers with a preliminary stability of 2.3×10⁻¹³/√τ based on the modulation transfer spectroscopy technique of ⁸⁵Rb 5S<inf>1/2</inf>–6P<inf>3/2</inf> transition. By the heterodyne experiment between the two ⁸⁵Rb spectrometers, we have measured the hyperfine separations of ⁸⁵Rb 6P<inf>3/2</inf>, and obtained the magnetic dipole constant and the electric quadrupole constant which are 8.220 MHz and 5.148 MHz respectively, not considering the systematic errors yet.

A small calcium beam optical frequency standard with fully-sealed vacuum tube

In this paper a small Calcium beam optical frequency standard utilizing fully-sealed Calcium beam vacuum tube owning smaller size compared with vacuum system with flanges is demonstrated. Adopting the electron shelving detection method, we detect the clock transition 657 nm saturation absorbing spectroscopy whose linewidth is 500 kHz. The instability of this small optical frequency standard is 6.8×10−14 at 1 second and 1.8×10−15 after 1000 seconds of averaging by comparing with another small Calcium beam optical frequency standard whose reported instability is 3.0×10−14 at 1 second. The optical part of the whole system is specially designed for robustness and miniaturization.

Miniaturized calcium beam optical frequency standard using fully-sealed vacuum tube with 10 −15 instability

We implement a miniaturized calcium beam optical frequency standard using specially-designed fully-sealed vacuum tube, and realize the comparison with another calcium beam optical clock whose vacuum tube is sealed by flanges. The electron shelving detection method is adopted to improve the signal-to-noise ratio of the clock transition spectroscopy, and the readout laser is locked by modulation-free frequency locking technology based on Doppler effect. Injection locking is carried out to boost the power of the 657 nm master clock transition laser, thus ensuring the comparison. The fractional instability of the miniaturized calcium beam optical frequency standard using fully-sealed vacuum tube is 1.8×10-15 after 1600 s of averaging. Total volume of the system except for electronics is about 0.3 m3. To our knowledge, its the first time to realize the optical frequency standard using fully-sealed vacuum tube. This work will promote the miniaturization and transportability of the optical clock based on atomic beam.

A 420 nm Blue Diode Laser for the Potential Rubidium Optical Frequency Standard

We report a 420 nm external cavity diode laser with an interference filter (IF) of 0.5 nm narrow-bandwidth and 79% high transmission, which is first used for Rb optical frequency standard. The IF and the cat-eye reflector are used for selecting wavelength and light feedback, respectively. The measured laser linewidth is 24 kHz when the diode laser is free running. Using this narrow-linewidth IF blue diode laser, we realize a compact Rb optical frequency standard without a complicated PDH system. The preliminary stability of the Rb optical frequency standard is at 1 s and decreases to at 1000 s. The narrow-linewidth characteristic makes the IF blue diode laser a well suited candidate for the compact Rb optical frequency standard.

Research on Cs active Faraday optical frequency standard with 459 nm laser pumping

Known as a unique optical clock, active optical clock has prior advantages to surpass the limitation of the conventional optical clock in potential stability. In this paper, we proposed an improved Cesium active Faraday optical frequency standard with 459 nm laser pumping. This scheme reduces the residual Doppler broadening in previous results with 852 nm laser pumping. The transmission is 2.4% and the bandwidth of the transmission peak is 12.3 MHz. It greatly narrows the bandwidth of Faraday anomalous dispersion optical filter and decreases the length of the bad cavity used in Cesium active Faraday optical frequency standard. This will be very helpful for further suppression of cavity pulling effect.