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Title: Photoacoustic trace detection of gases at the parts-per-quadrillion level with a moving optical grating

The amplitude of the photoacoustic effect for an optical source moving at the sound speed in a one-dimensional geometry increases linearly in time without bound in the linear acoustic regime. In this paper, use of this principle is described for trace detection of gases, using two frequency-shifted beams from a CO 2 laser directed at an angle to each other to give optical fringes that move at the sound speed in a cavity with a longitudinal resonance. The photoacoustic signal is detected with a high- Q , piezoelectric crystal with a resonance on the order of 443 kHz. The photoacoustic cell has a design analogous to a hemispherical laser resonator and can be adjusted to have a longitudinal resonance to match that of the detector crystal. Finally, the grating frequency, the length of the resonator, and the crystal must all have matched frequencies; thus, three resonances are used to advantage to produce sensitivity that extends to the parts-per-quadrillion level.
 [1] ;  [1] ;  [2] ;  [2] ;  [2] ;  [1]
  1. Brown Univ., Providence, RI (United States). Dept. of Chemistry
  2. Shandong Univ., Jinan (China). State Key Lab. of Crystal Materials
Publication Date:
Grant/Contract Number:
Published Article
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 114; Journal Issue: 28; Journal ID: ISSN 0027-8424
National Academy of Sciences, Washington, DC (United States)
Research Org:
Brown Univ., Providence, RI (United States); Shandong Univ., Jinan (China)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); Shandong Univ. (China)
Country of Publication:
United States
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; photoacoustics; trace detection; moving grating; piezocrystal; resonator
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1465968