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Title: Computational expressions for signals in frequency-modulation spectroscopy

In this study, general expressions for the signals in frequency-modulation spectroscopy (FMS) appear in the literature but are often reduced to simple analytical equations following the assumption of a weak modulation index. This is little help to the experimentalist who wants to predict signals for modulation depths of the order of unity or greater, where strong FMS signals reside. Here, we develop general formulas for FMS signals in the case of an absorber with a Voigt line shape and then link these expressions to an example and existing numerical code for the line shape. The resulting computational recipe is easy to implement and exercised here to show where the larger FMS signals are found over the coordinates of modulation index and modulation frequency. One can also estimate from provided curves the in-phase FMS signal over a wide range of modulation parameters at either the Lorentzian-broadening or Doppler-broadening limit, or anywhere in between by interpolation.
Authors:
 [1] ;  [1]
  1. Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
Publication Date:
OSTI Identifier:
1233522
Report Number(s):
LA--UR-15-20941
Journal ID: ISSN 0003-6935; APOPAI; TRN: US1600378
Grant/Contract Number:
AC52-06NA25396
Type:
Accepted Manuscript
Journal Name:
Applied Optics
Additional Journal Information:
Journal Volume: 54; Journal Issue: 16; Journal ID: ISSN 0003-6935
Publisher:
Optical Society of America (OSA)
Research Org:
Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS spectroscopy; frequency-modulation spectroscopy; spectroscopy modulation; susceptibility; phase modulation; absorption