671 nm雷射系統和中空陰極管鋰原子D譜線光譜

Abstract

我們實作一雷射波長為671 nm的穩定雷射系統，其設計為一Littrow配置的外腔式二極體雷射，具有精巧的結構、高穩定性、低成本和波長可調等特性。在操作電流100 mA下雷射輸出功率為13 mW。藉由同時控制雷射的壓電驅動器和雷射電流，可使雷射波長調整範圍達37 GHz。自由運行中的雷射與光頻梳雷射拍頻後可估計其線寬在6.25 ms內小於300 kHz。將雷射頻率鎖在一個法布立-培若腔體上，可得雷射頻率擾動小於35 kHz。我們調製雷射頻率在內部Ne氣壓為800 Pa之中空陰極管內產生鋰原子(Li 7) D譜線光譜，並且將雷射頻率鎖在此光譜上，長時間的雷射頻率擾動小於 600 kHz。 自製給雷射使用之穩定電流源，其電流在4小時內飄移小於0.4 μA，電流雜訊的方均根小於300 nA。此電流源的穩定度可媲美一般商用電流源。 我們另外使用此雷射來研究在中空陰極管的鋰原子(Li 7)D譜線飽和吸收光譜。此光譜有次都普勒特徵和一都普勒基座(Doppler pedestal)，導致都普勒基座的原因為速度改變碰撞(velocity-changing collisions)效應，也可能有自濺射效應(self-sputtering effect)的影響。

A stable 671 nm Littrow configuration ECDL (External cavity diode laser) system is constructed and designed with requirements of being compact, high stability, low-cost and tunable. The output power of this ECDL is 13 mW at 100 mA operation current. The frequency could be tuned by scanning the PZT of the ECDL and controlling the laser current at the same time. The tuning range can go up to 37 GHz. The free running linewidth is below 300 kHz at 6.25 ms by measuring the beat frequency with a fiber comb laser. The frequency fluctuation is below 35 kHz when the ECDL is locked to a Fabry-Perot cavity. Furthermore, by implementing frequency modulation on the ECDL, the laser frequency can be stabilized to the D line transition of Li 7 in the hollow cathode lamp with the long-term frequency fluctuation well below 600 kHz. A current driver is constructed to provide a stable current source to laser diode. The measured current drift is lower than 0.4 μA in a 4 hours period and the current noise is lower than 300 nA rms. The performance of current driver is comparable with that of commercial current drivers.