HeH+中紅外飽和吸收光譜量測

Saturated Absorption Spectrum Measurement of HeH+ in the Mid-Infrared

彭柏皓(Po-Hao Peng)

指導教授 ： 施宙聰

國立清華大學/電機資訊學院/光電工程研究所/碩士(2018年)

摘要

我們建立了一套高精密與高準確中紅外飽和吸收光譜儀，其包含碘分子穩頻雷射系統、可調式偏差鎖頻系統、光學參量振盪器 (Optical Parametric Oscillator, OPO)、光頻梳、偏差鎖頻系統與延伸負輝光放電管，光源可以產生2.6 μm~4 μm的中紅外光，閒波功率可達1.5 W以上。
頻率標準建立在碘分子穩頻系統上，再將OPO的泵浦光利用可調式偏差鎖頻系統鎖在碘分子穩頻系統，而OPO的信號波則用偏差鎖頻系統鎖在光頻梳上，利用調整OPO的泵浦光可以精準的改變OPO的閒波。
我們重架了碘分子穩頻系統，並重新設計可調式偏差鎖頻系統的線路以及相位延遲產生器，藉由改善OPO的泵浦光來提升閒波的精準度，其不準度可在8 kHz以下，且鎖頻時間可至12小時以上。我們亦增加了延伸負輝光放電管的磁場，並將OPO在放電管中的光改成Double Pass，以提高訊噪比。
我們用此套系統量測HeH+在基頻帶P(4)~R(4)共9條譜線，P(3)~R(3)的準確度皆在1 MHz以內，與其他團隊的誤差在1 MHz以下，而P(4)與R(4)的準確度則在5 MHz以內。在改善系統後，我們將P(1)的訊噪比提升至1.7倍，且延長積分時間還可再提升訊噪比。

關鍵字

飽和吸收光譜 ； 中紅外光 ； 碘分子穩頻雷射 ； 可調式偏差鎖頻系統 ； 光學參量振盪器

並列摘要

We built a high precision and high accuracy mid-IR saturated absorption spectrometer, including iodine stabilized laser system, tunable offset locking system, optical parametric oscillator (OPO), optical frequency comb, offset locking system and extended negative glow discharge tube. With the light source, we can generate mid-IR laser with wavelength from 2.6 μm to 4 μm. The power of the idler wave can output over 1.5 W.
We set the frequency standards on the iodine stabilized laser system, lock pump wave of OPO on the iodine stabilized laser system by tunable offset locking system, and lock signal wave of OPO on an optical frequency comb by offset locking system. So we can precise adjustment frequency of the idler wave with tune frequency of pump wave.
We rebuild the iodine stabilized laser system, and redesign circuits of the tunable offset locking system and its phase delay generator. Because improve the pump wave of OPO can promotion precision of the idler wave, and let its uncertainty claim to be low 8kHz. Locking time can increase to over 12 hours. We also increase magnetic field and absorption path in extended negative glow discharge tube to promotion signal-to-noise ratio.
We used this system to measurement 9 transitions of HeH+ in fundamental band. Among them, uncertainty of P(3) to R(3) is within 1 MHz, and uncertainty of P(4) and R(4) is within 5 MHz. After improving system, we increase the signal-to-noise ratio of P(1) to 1.7 times. If we extend the integration time, can increase SNR more.

並列關鍵字

Saturated Absorption Spectrum ； Mid-Infrared ； Iodine Stabilized Laser ； Tunable Offset locking System ； Optical Parametric Oscillator

參考文獻

[1] T. R. Hogness and E. G. Lunn, "The ionization of hydrogen by electron impact as interpreted by positive ray analysis," Phys. Rev., vol. 26, p. 44, 1925.

[2] D. E. Tolliver, G. A. Kyrala, and W. H. Wing, "Observation of the infrared spectrum of the helium-hydride molecular ion 4HeH+," Phys. Rev. Lett., vol. 43, p. 1719, 1979.

[3] A. Carrington, J. Buttenshaw, R. A. Kennedy, and T. P. Softley, "Observation of bound to quasibound vibration-rotation transitions in the HeH+ ion," Mol. Phys., vol. 44, p. 1233, 1981.

[4] P. Bernath and T. Amano, "Detection of the infrared fundamental band of HeH+," Phys. Rev. Lett., vol. 48, p. 20, 1982.

[5] M. W. Crofton, R. S. Altman, N. N. Haese, and T. Oka, "Infrared spectra of 4HeH+, 4HeD+,3HeH+, and 3HeD+," J. Chem. Phys., vol. 91, p. 5882, 1989.