Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
J Chem Phys. 2011 Jul 14;135(2):024202. doi: 10.1063/1.3597774.
Chirped-pulse millimeter-wave (CPmmW) spectroscopy is the first broadband (multi-GHz in each shot) Fourier-transform technique for high-resolution survey spectroscopy in the millimeter-wave region. The design is based on chirped-pulse Fourier-transform microwave (CP-FTMW) spectroscopy [G. G. Brown, B. C. Dian, K. O. Douglass, S. M. Geyer, S. T. Shipman, and B. H. Pate, Rev. Sci. Instrum. 79, 053103 (2008)], which is described for frequencies up to 20 GHz. We have built an instrument that covers the 70-102 GHz frequency region and can acquire up to 12 GHz of spectrum in a single shot. Challenges to using chirped-pulse Fourier-transform spectroscopy in the millimeter-wave region include lower achievable sample polarization, shorter Doppler dephasing times, and problems with signal phase stability. However, these challenges have been partially overcome and preliminary tests indicate a significant advantage over existing millimeter-wave spectrometers in the time required to record survey spectra. Further improvement to the sensitivity is expected as more powerful broadband millimeter-wave amplifiers become affordable. The ability to acquire broadband Fourier-transform millimeter-wave spectra enables rapid measurement of survey spectra at sufficiently high resolution to measure diagnostically important electronic properties such as electric and magnetic dipole moments and hyperfine coupling constants. It should also yield accurate relative line strengths across a broadband region. Several example spectra are presented to demonstrate initial applications of the spectrometer.
啁啾脉冲毫米波（CPmmW）光谱学是第一种用于毫米波区域高分辨率巡测光谱的宽带（每个脉冲多千兆赫）傅里叶变换技术。该设计基于啁啾脉冲傅里叶变换微波（CP-FTMW）光谱学[G.G. Brown、B.C. Dian、K.O. Douglass、S.M. Geyer、S.T. Shipman 和 B.H. Pate，Rev. Sci. Instrum. 79, 053103（2008）]，该技术可用于高达 20GHz 的频率。我们已经构建了一种仪器，可覆盖 70-102GHz 的频率区域，并且可以在单个脉冲中获取高达 12GHz 的光谱。在毫米波区域使用啁啾脉冲傅里叶变换光谱学面临的挑战包括可实现的样品极化较低、较短的多普勒去相时间以及信号相位稳定性问题。然而，这些挑战已部分得到克服，初步测试表明，与现有的毫米波光谱仪相比，在记录巡测光谱所需的时间方面具有显著优势。随着更强大的宽带毫米波放大器变得经济实惠，灵敏度的进一步提高有望实现。能够获取宽带傅里叶变换毫米波光谱使得能够快速测量具有足够高分辨率的巡测光谱，以测量电和磁偶极矩以及超精细耦合常数等具有诊断意义的电子特性。它还应该在宽带区域内产生准确的相对谱线强度。本文提供了几个示例光谱，以展示该光谱仪的初步应用。
