Due to external cavity, the external-cavity diode laser (ECDL) is sensitive to the harsh environment. It can serve as a very convenient tool for measuring or comparing acoustic responses and analysis of acoustic insulation characteristics of materials and mechanical structure. Focused on the ECDL, improvement of the laser acoustic responses and suppression of the laser system drift are critical. But the acoustically-induced vibration coupled with complex disturbance will contribute to the frequency fluctuation, therefore it is difficult to investigate the dynamic response characteristics of laser frequency to acoustic signals separately. In order to decouple the acoustic response from environmental noise and to reduce system drift, a frequency stabilization system by virtue of grating feedback and current feedback is demonstrated with the a wide-bandwidth loop. After recording the system response, the amplitude-frequency characters are achieved through fast Fourier transform (FFT). After analyzing the correlation of the laser frequency fluctuation and the acoustic stimulant signal’s frequency, the acoustic dynamic response characteristics of the ECDL is depicted experimentally. By contrasting the acoustic response characteristics of the ECDL with or without the acoustic proofing case, the acoustic insulating effect could be mapped directly. The experimental results show that the acoustic proofing case can not be remained valid for all frequency bands effectively. It can also act as the experimental criteria for optimizing the design of laser mechanical structures and acoustic insulation systems. Furthermore, this optical system could be employed as a detector extending to acoustic sensing or acoustic precise measurement.
We report on experimental preparation of the second-harmonic-wave laser and the single-mode squeezed vacuum state of 795 nm (rubidium atom D1 line) with periodically-poled KTiOPO4 (PPKTP) bulk crystals. By using a four-mirror bow-tie type ring doubling cavity we achieved ~111 mW of continuous-wave single-frequency ultra-violet (UV) laser radiation at 397.5 nm with ~191 mW of 795 nm fundamental-wave laser input. The corresponding doubling efficiency is 58.1%. To our knowledge, this is the highest doubling efficiency at 795 nm so far. Employing the 397.5 nm UV laser as a pump source of an optical parametric oscillator (OPO) with a PPKTP crystal, we achieved 5.6 dB of 795 nm single-mode squeezed vacuum output at analyzing frequency of 2 MHz. To our knowledge, this is the highest squeezing level of 795 nm single-mode squeezed vacuum so far. We analyzed the pump power dependence of the squeezing level, and concluded that UV laser induced losses of PPKTP crystal are main limiting factors for further improving the squeezing level. The generated 795 nm vacuum squeezing has huge potential applications in quantum memory and ultra-precision measurement with rubidium atoms.