Analysis of high-resolution spectra from a hybrid interferometric/dispersive spectrometer

Abstract

To more fully take advantage of a low-cost, small footprint hybrid interferometric/dispersive spectrometer, a mathematical reconstruction technique was developed to accurately capture the high-resolution and relative peak intensities from complex spectral patterns. A Fabry-Perot etalon was coupled to a Czerny-Turner spectrometer, leading to increased spectral resolution by more than an order of magnitude without the commensurate increase in spectrometer size. Measurement of the industry standard Hg 313.1555/313.1844 nm doublet yielded a ratio of 0.682, which agreed well with an independent measurement and literature values. The doublet separation (29 pm) is similar to the U isotope shift (25 pm) at 424.437 nm that is of interest to monitoring nuclear nonproliferation activities. Additionally, the technique was applied to LIBS measurement of the mineral cinnabar (HgS) and resulted in a ratio of 0.682. This reconstruction method could enable significantly smaller, portable high-resolution instruments with isotopic specificity, benefiting a variety of spectroscopic applications.

Laser Ablation Plasmas and Spectroscopy for Nuclear Applications

“…Effenberger and Scott 371 proposed an alternative method for performing high-resolution LIBS measurements by adding a low-cost Fabry-Perot etalon to the entrance slit of a 0.5 m focal length Czerny-Turner spectrometer. The performance of the instrument was demonstrated using the hyperfine doublet of the 313.2 nm Hg emission line, which exhibits a splitting of 29 pm, similar to the isotope shift for U. Ko et al 372 further developed the hybrid interferometric/dispersive technique by developing a method to reconstruct the high-resolution spectrum for LIBS measurements and showed improvement in the spectral resolution and accurate reconstruction of the peak ratios compared to conventional dispersive only measurements. Ultimately, isotope selective measurement of U was demonstrated for the first time using the hybrid interferometric/dispersive instrument in a LIBS measurement.…”

Hybrid interferometric/dispersive atomic spectroscopy of laser-induced uranium plasma

“…A spectral reconstruction method was developed to analyze the high-resolution fringes incident on the detector without presuming the distribution of the source spectrum. The mathematical model used for reconstructing the spectrum from a FP fringe pattern has been described and validated previously [24]. The accuracy of the reconstruction depends on proper alignment of the optical fiber, Fabry-Perot etalon and the entrance slit of the spectrometer.…”

“…To further validate the resolution in the isotope shift measurements, experimental data was interpolated and resampled to improve the sampling rate for reconstruction via the inversion method [24]. A low-pass filtering of the experimental data was also applied prior to reconstruction of the source spectrum to reduce the random spectral noise.…”

“…The current laboratory setup of the hybrid instrument is approximately the same size of DEMON and larger than the EMU-65. While the resolution of the instrument results from the combination of characteristics of all components of the light collection and detection system, the vast majority of the resolving power results from the use of the FP etalon [24]. Thus, replacing the 0.55 mm focal length spectrometer of the hybrid device with a more compact dispersive device, such as a miniature spectrometer, could substantially reduce the overall footprint of the instrument without sacrificing performance in this application.…”

“…Instrument performance was demonstrated using the hyperfine doublet of the 313.2 nm mercury emission line, which exhibits a splitting of 29 pm, similar to an isotope shift of uranium. Recently, a method was developed to reconstruct the high-resolution spectrum from a similar hybrid interferometric/dispersive LIBS instrument and showed improvement in spectral resolution and accurate determination of peak ratios compared to conventional pixel-towavelength schemes [24].…”