本實驗利用波長760 nm 的外腔式二極體雷射觀察了銣原子5S1/2-7S1/2雙光子躍遷，此波長恰好落在光通訊頻段的S 頻段(1460-1530 nm)的倍頻範圍內，自然線寬只有900 kHz，且躍遷頻率不受磁場影嚮，透過倍頻的機制，此雙光子躍遷是很好的光通訊頻段頻率標準，在高密度分波多工器(DWDM)光通訊系統中將有助於頻道的區分。
當雷射光功率為10 mW 時，譜線的訊雜比為280，半高全寬(FWHM)為
3MHz。透過調變頻率的技巧(FM spectroscopy)得到雷射穩頻所需的微分訊號，將760 nm 二極體雷射的頻率鎖在此雙光子躍遷的譜線上，鎖頻後的頻率不準確度在一秒的積分時間可達到7 kHz (2×10-11)。此外，經由摻鉺光纖光放大器(EDFA)及高效率的週期性極化反轉鈮酸鋰波導(PPLN waveguide)，將光通訊頻段所使用的1520 nm 外腔式二極體雷射放大至100 mW，然後倍頻至760 nm，倍頻光的功率可達10 mW。同樣利用調變頻率的方式得到微分訊號，並將此倍頻光的頻率鎖在銣原子5S1/2􀃆7S1/2 雙光子躍遷的譜線上，鎖頻後的頻率不準確度在一秒的積分時間可達9 kHz (2.5×10-11)。
之後，我們利用工研院量測中心所架設的飛秒光頻梳(Optical femtosecond comb)系統量測了此雙光子躍遷的絕對頻率，量測到的頻率不準確度為20 kHz。
經由絕對頻率的測量，得到之銣原子7S1/2 能階的超精細結構常數(Hyperfine constant)之不準度縮小為過去的四分之一。同時，銣原子5S1/2􀃆7S1/2 躍遷的同位素位移(Isotope shift)也首度被量測到。

Rubidium 5S1/2-7S1/2 two-photon transition has been observed using a 760 nm external cavity diode laser and a vapor cell. With 10 mW laser power, the SNR and linewidth of the transition is 280 and 3 MHz, respectively. The ECDL is stabilized on the transition to an uncertainty of 7 kHz (2*10-11) using FM spectroscopy.
Absolute frequencies of all hyperfine components in this transition have been measured to an uncertainty of 20 kHz using optical femtosecond comb. Different systematic effects are tabled. The uncertainty of hyper‾ne constant in rubidium 7S1/2 state is improved by a factor of four, comparing with previous best result. And for the first
time, isotope shift of this transition is measured to be 131.567(73) MHz.
By frequency doubling technique, a 1520 nm ECDL is stabilized on the two-photon transition. This provides a frequency standard in telecommunication band (1460-1530
nm, S-band).

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