A linewidth-narrowed and frequency-stabilized dye laser for application in laser cooling of molecules

Coherent photo-thermal noise cancellation in a dual-wavelength optical cavity for narrow-linewidth laser frequency stabilisation

Optical resonators are used for the realisation of ultra-stable frequency lasers. The use of high reflectivity multi-band coatings allows the frequency locking of several lasers of different wavelengths to a single cavity. While the noise processes for single wavelength cavities are well known, the correlation caused by multi-stack coatings has as yet not been analysed experimentally. In our work, we stabilise the frequency of a 729 nm and a 1069 nm laser to one mirror pair and determine the residual-amplitude modulation (RAM) and photo-thermal noise (PTN). We find correlations in PTN between the two lasers and observe coherent cancellation of PTN for the 1069 nm coating. We show that the fractional frequency instability of the 729 nm laser is limited by RAM at 1 × 10-14. The instability of the 1069 nm laser is at 3 × 10-15 close to the thermal noise limit of 1.5 × 10-15.

High resolution laser excitation spectra and Franck-Condon factors of A2Π−X2Σ+ electronic transition of MgF

Magnesium monofluoride (MgF) is proposed as an ideal candidate radical for direct laser cooling. Here, the rotationally resolved laser spectra of MgF for the A2Π− X2Σ+ electronic transition system were recorded by using laser induced fluorescence technique. The MgF radicals were produced by discharging SF6/Ar gas mixtures between the tips of two magnesium needles in a supersonic jet expansion. We recorded a total of 19 vibrational bands belonging to three sequences of Δ v=0, ±1 in the region of 348-370 nm. Accurate spectroscopic constants for both X2Σ+ and A2Π states are determined from rotational analysis of the experimental spectra. Spectroscopic parameters, including the Franck-Condon factors (FCFs), are determined from the experimental results and the Rydberg-Klein-Rees (RKR) calculations. Significant discrepancies between the experimentally measured and RKR-calculated FCFs are found, indicating that the FCFs are nearly independent of the spin-orbit coupling in the A2Π state. Potential energy curves (PECs) and FCFs determined here provide necessary data for the theoretical simulation of the laser-cooling scheme of MgF.

The hyperfine structure branching ratios and ab initio study on low-lying electronic states for 24Mg19F molecule

The potential energy curves (PECs) of the fourteen low-lying Λ-S electronic states, spectroscopic constants, transition properties for the ²⁴Mg¹⁹F molecule are calculated at the multi-reference configuration interaction level of theory. The spin-orbit coupling effects are also taken into account in the electronic structure calculations. Spectroscopic constants agree well with previously obtained theoretical and experimental values. Based on the potential energy curves and transition dipole moments, the highly diagonally distributed Franck-Condon factors (f₀₀ = 0.975, f₁₁ = 0.926) for the A²Π (v' = 0, 1) → X²Σ⁺ (v″ = 0, 1) transition are determined. Moreover, it is important to note that the dissociation energy (2.68 eV) of the B²Σ⁺ state is achieved for the first time. Then, employing a quantum effective Hamiltonian approach, we investigate the hyperfine structure branching ratios between the A²Π_1/2 state and the X²Σ_1/2⁺ state. And the numerically analyze is obtained for a simple one-dimension (1D) case on ²⁴Mg¹⁹F molecular MOT. We hope that these data can provide a helpful reference for the assignment and analysis of guiding further experimental spectroscopic measurements and laser cooling in experimental on the ²⁴Mg¹⁹F molecule.

Note: An in situ method for measuring the non-linear response of a Fabry-Perot cavity

The transfer cavity is a very important frequency reference for laser stabilization and is widely used for applications such as precision measurements and laser cooling of ions or molecules. But the non-linear response of the piezoelectric ceramic transducer (PZT) in the Fabry-Perot cavity limits the performance of the laser stabilization. Thus, measuring and controlling such non-linearity is essential. Here we report an in situ, optical method to characterize this non-linearity by measuring the resonant signals of a dual-frequency laser. The differential measurement makes it insensitive to the laser and cavity drifts, while maintaining a very high sensitivity. It can be applied for various applications with PZTs, especially in an optical lab.