Search Results (2)

The single-step Rydberg excitation of cesium atoms requires a 319 nm ultraviolet laser with a narrow laser linewidth, high frequency stability, and high output power. To meet these requirements, in this work, we construct a high-power, single-frequency UV laser system at this wavelength. In this system, the frequency stabilization of the 1560.492 nm seed laser is critical to the performance of the ultraviolet laser. We employ nonlinear frequency conversion technology, the 1560.492 nm laser is frequency-doubled to 780.246 nm via a single pass through a PPLN crystal, and function integration is realized based on the modular parameter adjustment interface provided by the PyRPL software. Subsequently, the 1560.492 nm laser is stabilized to the $D_2$ hyperfine transition line of Rb-87 atoms using polarization spectroscopy (PS) and radio-frequency-modulated saturation absorption spectroscopy (RF-SAS). A comparative study of these two techniques shows that RF-SAS achieves superior stabilization performance, with the residual frequency fluctuation of the frequency-doubled laser being 1.07 MHz over 30 min. According to frequency doubling theory, the actual residual frequency fluctuation of the 1560.492 nm fundamental-frequency laser can be calculated as 0.535 MHz. Compared with our earlier scheme that utilized an ultra-low-expansion (ULE) optical cavity as a frequency reference, the present scheme eliminates the long-term drift induced by environmental factors. In contrast to frequency stabilization relying on discrete instruments, this integrated scheme significantly reduces the cost, simplifies the system architecture, saves space, and greatly enhances the flexibility and controllability of the system. It therefore provides a reliable and cost-effective solution to ensure the portability and practicability of high-performance UV laser sources. This high-precision frequency stabilization scheme directly guarantees the performance of the 319 nm UV laser, suppressing its linewidth below 10 kHz. Thus, it fully meets the stringent laser linewidth and frequency stability requirements for the single-step Rydberg excitation of cesium atoms and provides a reliable light source foundation for subsequent precision spectroscopic measurements. Full article

In recent years, the fabrication of materials with large nonlinear optical coefficients and the investigation of methods to enhance nonlinear optical performance have been in the spotlight. Herein, the bismuth telluride (Bi₂Te₃) thin films were prepared by radio-frequency magnetron sputtering and annealed in vacuum at various temperatures. The structural and optical properties were characterized and analyzed using X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, spectroscopic ellipsometry, and UV/VIS/NIR spectrophotometry. The third-order optical nonlinearities of Bi₂Te₃ thin films were investigated using the Z-scan technique, employing a 100 fs pulse width at an 800 nm wavelength. It is found that the crystallinity and the average grain size of the films increase with the annealing temperature. Meanwhile, the extinction coefficient of the annealed films increased, accompanied by a redshift in the optical bandgap. All samples exhibit pronounced saturable absorption and self-focusing behaviors. The nonlinear absorption coefficient and nonlinear refractive index of Bi₂Te₃ films annealed at 300 °C were found to be 2.44 times and 1.85 times higher than those of the as-deposited films, respectively. These findings demonstrate that annealing treatment is an effective approach to tuning the crystalline structure and linear optical properties of Bi₂Te₃ films while simultaneously enhancing their nonlinear optical performance. Full article