Sensitive and single-shot OH and temperature measurements by femtosecond cavity-enhanced absorption spectroscopy.
Opt Lett
; 47(13): 3171-3174, 2022 Jul 01.
Article
in En
| MEDLINE
| ID: mdl-35776577
ABSTRACT
In many low-temperature plasmas (LTPs), the OH radical and temperature represent key properties of plasma reactivity. However, OH and temperature measurements in weakly ionized LTPs are challenging, due to the low concentration and short lifetime of OH and the abrupt temperature rise caused by fast gas heating. To address such issues, this Letter combined cavity-enhanced absorption spectroscopy (CEAS) with femtosecond (fs) pulses to enable sensitive single-shot broadband measurements of OH and temperature with a time resolution of â¼180 ns in LTPs. Such a combination leveraged several benefits. With the appropriately designed cavity, an absorption gain of â¼66 was achieved, enhancing the actual OH detection limit by â¼55× to the 1011 cm-3 level (sub-ppm in this work) compared with single-pass absorption. Single-shot measurements were enabled while maintaining a time resolution of â¼180â
ns, sufficiently short for detecting OH with a lifetime of â¼100 µs. With the broadband fs laser, â¼34,000 cavity modes were matched with â¼95 modes matched on each CCD pixel bandwidth, such that fs-CEAS became immune to the laser-cavity coupling noise and highly robust across the entire spectral range. Also, the broadband fs laser allowed simultaneous sensing of many absorption features to enable simultaneous multi-parameter measurements with enhanced accuracies.
Full text:
1
Collection:
01-internacional
Database:
MEDLINE
Type of study:
Diagnostic_studies
Language:
En
Journal:
Opt Lett
Year:
2022
Type:
Article