Browsing by Author "Davis, Nicholas M."
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item Open Access Compact methane sensor using an integrating sphere and interband cascade laser at 3313 nm(Elsevier, 2023-04-23) Davis, Nicholas M.; Francis, Daniel; Hodgkinson, Jane; Tatam, Ralph P.We present a sensor for gas detection utilising an integrating sphere and interband cascade laser for tunable diode laser absorption spectroscopy (TDLAS). Measurements were made of the methane absorption line at 3313 nm using an integrating sphere with an effective pathlength of 70.1 cm. Gas concentrations were estimated from normalised absorption spectra with line fitting to 7 absorption lines within the scan. Testing showed that measurements were linear for methane in synthetic air for concentrations in the range 0-50ppm. With an averaging time of 20 seconds, the noise-equivalent methane concentration was 180ppb (1σ). The system requires minimal alignment, with preliminary measurements indicating the system is insensitive to vibration and misalignment of the laser input. The lack of alignment optics also allows it to be compact (190x170x120mm) and robust.Item Open Access Sensitive detection of methane at 3.3 μm using an integrating sphere and interband cascade laser(Society of Photo-optical Instrumentation Engineers, 2016-04-29) Davis, Nicholas M.; Hodgkinson, Jane; Francis, Daniel; Tatam, Ralph P.Detection of methane at 3.3μm using a DFB Interband Cascade Laser and gold coated integrating sphere is performed. A 10cm diameter sphere with effective path length of 54.5cm was adapted for use as a gas cell. A comparison between this system and one using a 25cm path length single-pass gas cell is made using direct TDLS and methane concentrations between 0 and 1000 ppm. Initial investigations suggest a limit of detection of 1.0ppm for the integrating sphere and 2.2ppm for the single pass gas cell. The system has potential applications in challenging or industrial environments subject to high levels of vibration.Item Open Access Spectroscopic gas detection using a Bragg grating - stabilized external cavity laser, custom written in planar integrated silica-on-silicon(Optical Society of America, 2019-09-25) Davis, Nicholas M.; Lynch, S. F.; Gates, J. C.; Hodgkinson, Jane; Smith, P. G. R.; Tatam, Ralph P.We present the development of an external cavity Bragg grating stabilized laser for tunable diode laser spectroscopy (TDLS). Our design uses a planar integrated silica-on-silicon platform incorporating a custom written Bragg grating as the wavelength-selective element of the laser cavity. We have developed a prototype singlemode laser at 1651 nm and performed a detailed characterization of its performance for the purpose of spectroscopic measurement of methane at this wavelength using a 25 cm path-length single-pass cell. Mode hop-free tuning of 0.13 nm has been demonstrated at frequencies of up to 10 kHz. A single-point limit of detection for TDLS of ΔI/I0 = 8.3 × 10−5 AU was achieved, which is consistent with the performance of standard distributed feedback lasers. The new device exhibits a side-mode suppression ratio of −40 dB and a low RIN of <−150 dB/Hz, and thus avoids the high levels of noise or instability normally associated with larger, mechanically driven external cavity lasers. The silica-on-silicon platform has the potential for low-volume manufacturing of special lasers at the custom wavelengths required for gas detection, without the need for investment in foundry solutions.