Two new long-pass cells for infrared and visible spectroscopy

Abstract

A multiplex infrared-visible sum-frequency spectrometer with wavelength tunability of the visible probe A new simple and low cost scattered transmission accessory for commercial double beam ultraviolet-visible spectrophotometers Rev.We describe two very long path absorption cells for sensitive laser absorption spectroscopy which are based on a design first described by Chernin and Barskaya ͓Appl. Opt. 30, 51 ͑1991͔͒. The cells distribute a nearly arbitrary number of spots across both dimensions of the field mirror in an efficient, compact array: confining up to 500 traversals in a 26 cm diam cooled cylindrical vacuum housing. The first cell, constructed at Denison University, is one of several multipass cells in the Laser Spectroscopy Laboratory used in the visible and near infrared ͑400-1100 nm͒. Optical paths of up to 1 km have been attained in this 3 m long cell at pressures from near vacuum to several atmospheres. The cell operates at temperatures down to 125 K. Conventional Pyrex optics are used. The second cell is part of a long path laboratory laser absorption spectrometer used in the thermal infrared: 350-2000 cm Ϫ1 at Goddard Space Flight Center. Path lengths up to 476 m have been achieved at frequencies less than 500 cm Ϫ1 . Two unique features of the Goddard cell are the piezoelectric micrometers, which simplify considerably the controls for the optical alignment, and the diamond-turned spherical mirrors, which significantly reduce the cost and the complexity of cryogenic operation. In addition, we discuss criteria for determining the optimal pathlength of a given multipass cell for the measurement of weak spectral lines.

Line positions and line strengths for the 3← electric quadrupole band of H2Σg+1

“…2,3 We determined the positions of the Q lines by interpolation from known water lines in some of our spectra from water contamination. Pressure shifts in the hydrogen 3-0 band have recently been measured at −1 ϫ 10 −7 cm −1 / Pa. 34 At the maximum pressure of our experiments, this would result in a shift of −0.03 cm −1 . 33 The resulting line centers in the limit of zero pressure are given in Table I to within ±0.03 cm −1 .…”

“…We identified the water lines using the results of Toth. 34 Errors introduced into our line center determinations from pressure shifts are therefore less than the precision of our determinations. Pressure shifts in the hydrogen 3-0 band have recently been measured at −1 ϫ 10 −7 cm −1 / Pa. 34 At the maximum pressure of our experiments, this would result in a shift of −0.03 cm −1 .…”

Incoherent broad-band cavity-enhanced absorption spectroscopy

“…Classical experimental schemes employ multi-pass cells according to White [White42,White76] or Herriot and Schulte [Herriot65]. Many modifications and improvements of these original setups have been developed [Chernin01,Steyert01], which are associated with a loss of experimental simplicity. Many long path length approaches use narrow-band tunable diode-lasers (TDLAS [Reid78,Werle98]) in combination with multi-pass cells or in open path experiments.…”

A broadband optical cavity spectrometer for measuring weak near-ultraviolet absorption spectra of gases

“…Extensive measurement times are required if the pathlength through the sample is relatively short (on the order of metres, say) which imposes stringent conditions on the stability of both the chemical source and the spectrometer during the measurement. Multipass cells can extend the pathlength from hundreds of metres to a few kilometres, but require large sample volumes (Steyert et al, 2001). Optical cavities provide an alternative means of obtaining a long effective pathlength of light (typically several kilometres) through the sample, and techniques exploiting this property include cavity ring-down spectroscopy and cavity-enhanced absorption spectroscopy (Mazurenka et al, 2005).…”