Saturated absorption spectroscopy of rubidium and feedback control of LASER frequency for Doppler cooling

ZhengTan, Yongcheng, Xian-pingSun +4 more

G. N. Botha

In the presented study a diode laser was characterised and used for spec- troscopy, measuring the resonance lines of atomic rubidium. The characteristics of diode lasers and external cavity diode lasers (ECDL) for the purposes of ab- sorption spectroscopy were investigated and an experimental setup for tunable diode laser spectroscopy using an ECDL was developed. In external cavity diode lasers, the advantages of low cost, small size and e ciency of a diode laser is combined with tunability and a narrow frequency bandwidth. The ECDL was applied in experimental setups for absorption spectroscopy and saturated ab- sorption spectroscopy. Measurement of the absorption of atomic rubidium's D2 line near 780 nm is discussed. The Doppler broadened, as well as the Doppler free spectrum of the ne and hyper ne structure of the D2 line were measured and is discussed. Finer control of the ECDL's stability and frequency, using a servo circuit, were investigated and tested. An overview is given of laser cool- ing and trapping of neutral rubidium atoms, which is the main application the ECDL were developed for.

Song-Quan Shang

Thomas Edison. Stark

Laser cooling experiments developed in the last decade enable physicists to slow down and spatially confine neutral atoms of a gas, thus lowering the temperature of trapped atoms into the μK range. One of the challenges associated with laser cooling is to stabilize a laser so that its output frequency matches that of a hyperfine structure transition and has an absolute stability of several MHz. In this project, we establish the groundwork for future laser cooling experiments with Rb by performing saturated-absorption Doppler-free spectroscopy studies. We acquire Doppler-free spectra of Rb that resolve individual hyperfine structure transitions, including the transition that the laser must excite in laser cooling experiments. The spectra we obtained can readily be repeated and the experimental apparatus can provide the feedback for an electronic laser stabilization circuit.

Junye Zhao, Yongbiao Yang, Lulu Zhang +2 more

The utilization of atomic or molecular spectroscopy for frequency locking of single-frequency laser to improve laser frequency stability plays an important role in the experimental investigation of optically pumped atomic magnetometers, atomic clocks, laser cooling and trapping of atoms, etc. We have experimentally demonstrated a technique for frequency stabilization of a single-frequency laser employing the bright state spectroscopy (BSS) with a rubidium atomic vapor cell. By utilizing the counter-propagating dual-frequency 795 nm laser beams with mutually orthogonal linear polarization and a frequency difference of 6.834 GHz, which is equal to the hyperfine splitting of rubidium-87 ground state 5S1/2, an absorption-enhanced signal with narrow linewidth at the center of Doppler-broadened transmission spectroscopy is observed when continuous scanning the laser frequency over rubidium-87 D1 transition. This is the so-called BSS. Amplitude of the absorption-enhanced signal in the BSS is much larger compared with the conventional saturation absorption spectroscopy (SAS). The relationship between linewidth and amplitude of the BSS signal and laser beam intensity has been investigated. This high-contrast absorption-enhanced BSS signal has been employed for the laser frequency stabilization. The experimental results show that the frequency stability is 4.4×10−11 with an integration time of 40 s, near one order of magnitude better than that for using the SAS.

Shrabana Chakrabarti