Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Off-axis QEPAS using a pulsed nanosecond Mid-Infrared Optical Parametric
  Oscillator   A trace gas sensor, based on quartz-enhanced photoacoustic spectroscopy
(QEPAS), consisting of two acoustically coupled micro-resonators (mR) with an
off-axis 20 kHz quartz tuning fork (QTF) is demonstrated. The complete
acoustically coupled mR system is optimized based on finite element simulations
and experimentally verified. The QEPAS sensor is pumped resonantly by a
nanosecond pulsed single-mode mid-infrared optical parametric oscillator (MIR
OPO). The sensor is used for spectroscopic measurements on methane in the 3.1
um to 3.5 um wavelength region with a resolution bandwidth of 1 cm^-1 and a
detection limit of 0.8 ppm. An Allan deviation analysis shows that the
detection limit at optimum integration time for the QEPAS sensor is 32
ppbv@190s and that the background noise is solely due to the thermal noise of
the QTF.

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The categories of this paper are: eess
2
The categories of this paper are: math
29
The categories of this paper are: funct-an
31
The categories of this paper are: ao-sci
22
The categories of this paper are: chao-dyn
37
The categories of this paper are: supr-con
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The categories of this paper are: cmp-lg
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The categories of this paper are: comp-gas
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The categories of this paper are: nucl-ex
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The categories of this paper are: hep-ex
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The categories of this paper are: q-alg
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The categories of this paper are: q-fin
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The categories of this paper are: gr-qc
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The categories of this paper are: adap-org
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The categories of this paper are: q-bio
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The categories of this paper are: nucl-th