| Summary: | 博士 === 國立交通大學 === 光電工程系所 === 93 === Optical transitions in molecular iodine often provide stable references for precision spectroscopy and their hyperfine structure components have also been widely used in laser frequency stabilization. The molecular iodine lines near 532 nm have stronger absorption than red transitions and readily are carried out by diode-pumped, frequency-doubled solid-state Nd:YAG lasers. Moreover, the 2001 meeting of Consultative Committee for Length led the a10 component of R(56) 32-0 transition of 127I2 at 532 nm for the optical frequency standard.
Its pressure shift and power shift has been reported. However, the characteristics of the a10 component including linewidth, pressure broadening, and power broadening have not been investigated systematically. To further investigate the above-mentioned characteristics, we use the dependence of the peak amplitude of the third-derivative signal on the modulation width to determine the linewidth of the hyperfine structure a10 component of R(56) 32-0 transition. We also use the same method to investigate pressure broadening and power broadening of the a10 component.
In general, the hyperfine splitting is measured by heterodyne technique. However, not every laboratory could set up two iodine-stabilized lasers for measuring hyperfine splitting. Therefore, we study a method in which uses only one laser with a double-passed acousto-optic modulator frequency shifter replacing heterodyne technique. We use the R(56) 32-0 transition of 127I2 at 532 nm as an example. We have successfully measured the hyperfine splitting. Using the a10 component as a reference, the difference of the hyperfine splitting between Consultative Committee for Length and our results is within 20 kHz.
Besides the diode-pumped, frequency doubled Nd:YAG laser at 532 nm, we are also interesting in using diode lasers for frequency stabilization because of their smaller size, larger tuning range, higher power, and compactness. Frequency stabilization of the external cavity diode laser to the iodine hyperfine structure components using extra-cavity iodine cell has been extensively studied and reported.
The diode laser at 657 nm has the characteristics of lower cost and higher power than that at 633 nm. Therefore, we use the 657 nm ECDL to investigate the saturation spectrum of the hyperfine structure components of P(84) 5-5 transition of 127I2 at 657.483 nm for frequency stabilization of our ECDL laser. We have obtained the hyperfine structure components of P(84) 5-5 transition with a SNR of 1000 at 1 s time constant. The diode laser is frequency stabilized to the hyperfine component o of the saturated absorption signal. The frequency stability better than 10 kHz is achieved. Our scheme can be applied to ECDL at other wavelengths.
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