Rapid Scan Mid-IR Diode Laser Spectrometer

We have designed and constructed an astigmatic cell rapid scanning infrared spectrometer to complement the performance of our cavity ring down spectrometer. Although cavity ring down technique offers superior sensitivity for trace absorption, its dynamic range is limited. For molecular systems with sufficient absorption, the rapid scanning technique discussed here is a great choice. The additional advantage of this technique is that a spectrum covering a few wavenumbers can be obtained in a few miliseconds. This makes it a powerful instrument for spectroscopic investigations that require large search ranges.

Ref: Z. Su, W. S. Tam, and Y. Xu, J. Chem. Phys., 2006, 124, 024311.

The spectrometer consists of four major components: the vacuum chamber (left) that houses the molecular beam and astigmatic cell assemblies, the infrared detector (middle), the laser source (right), and the hardware and software to control the experiments (not shown).

Astigmatic Multi-Path Cell Assembly


Inside the vacuum chamber sits a homemade astigmatic multi-path cell assembly (bottom middle). The two astigmatic mirrors are separated by 20 cm and are adjusted to trace out the Lissajous patterns on the back (bottom left) and the front (bottom right) mirrors. We typically use the 182-pass configuration (top) which gives us a significant increase in the total absorption path. This accounts, in part, for the high sensitivity of our spectrometer.