| Summary: | 碩士 === 國立臺灣大學 === 物理研究所 === 98 === Frequency standard plays a crucial role in metrology. It is applied in fundamental science and industry (such as measurement of fundamental physics constants, spectrum, and astronomy). In the past, definition of frequency standard was based on the spectral line of atoms, but this method got involved in broad bandwidth region. Thanks to the development of femtosecond mode-locked laser and photonic crystal fiber, frequency standard nowadays covers from visible to infrared region.
In this article we use a Ti:Sapphire laser as a femtosecond mode-locked laser to build up a femtosecond frequency comb laser. Its feature is the same intervals between frequency modes, and that’s where the word, “comb”, comes from. The optical frequency of the nth mode of the mode-locked laser can be expressed as:fn=nfrep+fo,
where frep is repetition rate and fo is offset frequency. We apply method of self- reference to build up the comb laser. However, there’s a certain uncertainty of fn, since n has a order of magnitude about 10^6 so as to the error-bond of n. For this concern, beat note between a frequency stabilized diode laser at 822nm and our comb laser is served as an error signal to feedback and reduce the uncertainty of the comb laser.
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