Dr. Pei-Ling Luo, IAMS Assistant Research Fellow, completed her Ph.D. at National Tsing Hua University under the tutelage of Prof. Jow-Tsong Shy. After her postdoctoral fellowships in Prof. T. W. Hänsch’s group at the Max Planck Institute of Quantum Optics and Prof. Yuan-Pern Lee’s lab at National Chiao Tung University, she joined IAMS in August 2018. Her research interest is in developing midinfrared dual-comb spectrometers for studying key atmospheric molecules and free radicals. Today we visited Dr. Luo to hear more about her exciting work.
A: What is a dual-comb spectrometer?
Dr. Pei-Ling Luo (PLL): A dual-comb spectrometer (DCS), a multiheterodyne Fourier transform spectrometer based on two frequency combs at slightly different repetition frequencies, enables the simultaneous achievement of broad bandwidth, rapid measurement, and high resolution. DCS is a promising successor to conventional Fourier-transform infrared spectroscopy (FTIR), but unlike FTIR, a DCS can offer sensitive spectral measurements with virtually no instrument line shape. Therefore, DCS can be a powerful tool for accurate quantitative spectroscopy.
A: What type of dual-comb spectrometer you are making?
PLL: Most of the DCSs are designed based on the mode-locked lasers; however, the optical resolution and spectral sampling speed of these DCSs lacks flexibility because of the narrow tuning range of the repetition rate of the mode-locked laser combs. In our lab, we set up a highly flexible DCS based on electro-optic frequency combs near 3 µm. Our DCS offers a tunable spectral range of >500 nm and adjustable comb mode spacing (optical resolutions) from a few hundred MHz to a few GHz. Both precision spectral metrology and fast molecular sampling could be implemented by employing our rapidly tunable DCS.
A: What specific topic are you working on using your dual-comb spectrometer?
PLL: We are interested in accurate quantitative spectral measurements of key atmospheric molecules and free radicals. By employing the DCS, we will take advantage of the rapid broadband spectral acquisition for systematic measurements in different conditions. In addition, our system could be implemented for studying chemical reactions with a distinguishing probe of each species.
A: Why did you choose to use dual-comb for such problems? Could you talk more about it?
PLL: There are two conventional methods: one is Michelson interferometer-based FTIR and the other is a tunable CW laser-based spectrometer. FTIR has broad spectral measurement capability; however, it lacks sensitivity and typically requires several hours for recording a high-resolution spectrum. By contrast, by using a CW laser-based spectrometer, the sensitivity can be improved by combining it with the cavity-enhanced absorption system, but the spectral lines are measured one by one, taking a long time to record the entire spectrum. The DCS has the unique capability of recording a broadband spectrum in a short data acquisition time. By employing the DCS, we can monitor the signal variations of multiple species simultaneously in real time.
A: Your research topics seem quite challenging. Do you have any group members or support?
PLL: Although my lab currently only has a few people, our experimental system is very stable, and the proposed research projects are progressing step by step. In addition, I really appreciate the support from all of IAMS members, particularly from the groups of Prof. Chi-Kung Ni, Prof. Wen-Bih Tzeng, and Prof. Jr-Min Lin. They give me many useful bits of advice and helped in building my new lab. Finally, I would like to acknowledge our director Prof. Kuei-Hsien Chen, who fully supports my research projects. IAMS offers a very good research environment that can help people to overcome challenges and accomplish tasks.