Saturated-absorption spectroscopy revisited: atomic transitions in strong magnetic fields (>20 mT) with a micrometer-thin cell

Frequency stabilization of multiple lasers to a reference atomic transition of Rb

Modern atomic clocks based on the interrogation of an atomic transitions in the optical regions require multiple lasers at different wavelength for producing atomic ions, trapping and laser cooling of neutral atoms or atomic ions. In order to achieve highest efficiency for laser cooling or any other atomic transition, frequencies of each of the lasers involved need to be stabilized by mitigating its drifts or fluctuations arise due to ambient temperature variation or other kind of perturbations. The present article describes simultaneous frequency stabilization of multiple number of lasers, required for production and laser cooling of ytterbium (¹⁷¹Yb) ions, to a reference transition frequency of rubidium (Rb) atoms. In this technique, a diode laser operating at ~ 780 nm is frequency stabilized to one of the Doppler broadening-free absorption peak of rubidium atoms (⁸⁵Rb) and then used as a reference frequency for calibrating a wavelength meter and subsequent simultaneous frequency stabilization of four lasers operating at different wavelengths.

Wide range linear magnetometer based on a sub-microsized K vapor cell

³⁹K atoms have the smallest ground state (²S_1/2) hyperfine splitting of all the most naturally abundant alkali isotopes and, consequently, the smallest characteristic magnetic field value B₀=A_²S1/2/μ_B≈170G, where A_²S1/2 is the ground state's magnetic dipole interaction constant. In the hyperfine Paschen-Back regime (B≫B₀, where B is the magnitude of the external magnetic field applied on the atoms), only eight Zeeman transitions are visible in the absorption spectrum of the D₁ line of ³⁹K, while the probabilities of the remaining 16 Zeeman transitions tend to zero. In the case of ³⁹K, this behavior is reached already at relatively low magnetic field B>B₀. For each circular polarization (σ^-,σ⁺), four spectrally resolved atomic transitions having sub-Doppler widths are recorded using a sub-microsized vapor cell of thickness L=120-390nm. We present a method that allows to measure the magnetic field in the range of 0.1-10kG with micrometer spatial resolution, which is relevant in particular for the determination of magnetic fields with large gradients (up to 3 G/µm). The theoretical model describes well the experimental results.

A simple extended-cavity diode laser using a precision mirror mount

We have developed an extended-cavity diode laser (ECDL) with a simple design by using a commercial precision mirror mount with minor modifications. Our design allows tuning of the external cavity configuration by tweaking the volume holographic grating without troublesome changes in the beam path of the laser output. The mode-hop-free tuning range of the presented ECDL is about 8 GHz with a linewidth of 475 kHz.

Dark resonance formation with magnetically induced transitions: extension of spectral range and giant circular dichroism

Dark resonances were formed via electromagnetically induced transparency for the first time, to the best of our knowledge, involving magnetically induced ΔF=±2 atomic transitions of alkali metal atoms, which are forbidden at zero magnetic field. The probability of these transitions undergoes rapid growth when 300-3000 G magnetic field is applied, allowing formation of dark resonances, widely tunable in the GHz range. It is established that for ΔF=+2 (ΔF=-2) transition, the coupling laser tuned to ΔF=+1 (ΔF=-1) transition of the hyperfine Λ-system must be σ⁺ (σ^-) polarized, manifesting anomalous circular dichroism.

Simultaneous two-photon resonant optical laser locking (STROLLing) in the hyperfine Paschen-Back regime

We demonstrate a technique to lock simultaneously two laser frequencies to each step of a two-photon transition in the presence of a magnetic field sufficiently large to gain access to the hyperfine Paschen-Back regime. A ladder configuration with the 5S_1/2, 5P_3/2, and 5D_5/2 terms in a thermal vapor of Rb87 atoms is used. The two lasers remain locked for more than 24 h. For the sum of the laser frequencies, which represents the stability of the two-photon lock, we measure a frequency instability of less than the Rb D₂ natural linewidth of 6 MHz for nearly all measured timescales.