Kaya G., Keskin A., Kaya N.
JOURNAL OF INSTRUMENTATION, cilt.21, sa.09, ss.1-13, 2026 (SCI-Expanded, Scopus)
-
Yayın Türü:
Makale / Tam Makale
-
Cilt numarası:
21
Sayı:
09
-
Basım Tarihi:
2026
-
Doi Numarası:
10.1088/1748-0221/21/09/p09049
-
Dergi Adı:
JOURNAL OF INSTRUMENTATION
-
Derginin Tarandığı İndeksler:
Scopus, Science Citation Index Expanded (SCI-EXPANDED), Compendex, Index Islamicus, INSPEC
-
Sayfa Sayıları:
ss.1-13
-
Çanakkale Onsekiz Mart Üniversitesi Adresli:
Evet
Özet
Abstract
Atmospheric methane (CH
4
) monitoring requires an optimal
balance between ultra-high sensitivity and mechanical
field-readiness. Conventional multi-pass architectures, such as
Herriott cells, are fundamentally constrained by rigid geometries
and alignment sensitivities that limit real-time optimization
capability. To overcome this limitation, we introduce an angularly
tunable circular multi-pass absorption cell (CMPC) integrated with
digital wavelength modulation spectroscopy (WMS). By leveraging a
20 cm radius “optical cage” architecture, continuous optical
path-length tunability is achieved through precise beam injection
angle control, resulting in a large effective optical path length of
134.8 m via 337 reflections. Targeting the R
4
transition near
1.651 μm ensures strong spectral isolation from ambient
H
2
O and CO
2
interference. The system incorporates a balanced
dual-beam detection scheme that suppresses common-mode noise and
laser intensity fluctuations, yielding a signal-to-noise ratio (SNR)
of 180 and a short-term precision of 50.1 ppb. Allan deviation
analysis confirms a detection limit of 55 ppb at 1 s integration
time, reaching an ultimate precision of 6.25 ppb at an optimum
integration time of 841 s. These results demonstrate that the
proposed architecture provides a compact, mechanically robust, and
highly sensitive alternative to conventional fixed-geometry methane
sensing systems.