Performance analysis and small signal identification of time-resolved stand-off Raman spectroscopy system

Xia, Jiabin; Yao, Qi-Feng; Zhu, Lianqing; Dong, Mingli; Lou, Xiaoping

doi:10.1016/j.vibspec.2019.01.001

Cited by 6 publications

(3 citation statements)

References 33 publications

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“…The reason why the TG principle plays an important role in this method stems from the need to reduce the disturbing amount of fluorescence and the background radiation of ambient light from the often unknown heterogeneous sample matrices under inspection. Often, a pulsed laser system around the fluorescence maximum at λ exc = 532 nm, or in the UV-region, with very sensitive and gated detectors (ICCDs or SPADs), is employed for this type of application [128,129]. Recently, Kekkonen et al (2018) proposed CMOS SPAD detectors for remote Raman detection to further reduce size, price and complexity, with an additional adjustable time-correlation option, for a TG standoff Raman setup.…”

Section: Tg Standoff Raman Detectionmentioning

confidence: 99%

Time-gated Raman spectroscopy – a review

Kögler

Heilala²

2020

Meas. Sci. Technol.

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Time-gated (TG) Raman spectroscopy (RS) has been shown to be an effective technical solution for the major problem whereby sample-induced fluorescence masks the Raman signal during spectral detection. Technical methods of fluorescence rejection have come a long way since the early implementations of large and expensive laboratory equipment, such as the optical Kerr gate. Today, more affordable small sized options are available. These improvements are largely due to advances in the production of spectroscopic and electronic components, leading to the reduction of device complexity and costs. An integral part of TG Raman spectroscopy is the temporally precise synchronization (picosecond range) between the pulsed laser excitation source and the sensitive and fast detector. The detector is able to collect the Raman signal during the short laser pulses, while fluorescence emission, which has a longer delay, is rejected during the detector dead-time. TG Raman is also resistant against ambient light as well as thermal emissions, due to its short measurement duty cycle.In recent years, the focus in the study of ultra-sensitive and fast detectors has been on gated and intensified charge coupled devices (ICCDs), or on CMOS single-photon avalanche diode (SPAD) arrays, which are also suitable for performing TG RS. SPAD arrays have the advantage of being even more sensitive, with better temporal resolution compared to gated CCDs, and without the requirement for excessive detector cooling. This review aims to provide an overview of TG Raman from early to recent developments, its applications and extensions.

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Section: Tg Standoff Raman Detectionmentioning

confidence: 99%

Time-gated Raman spectroscopy – a review

Kögler

Heilala²

2020

Meas. Sci. Technol.

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“…10 Time-gating was successfully used by many research groups in their standoff Raman instruments. [11][12][13][14][15] However, utilizing time-gating methodologies has disadvantages. Utilizing high peak power, low duty cycle lasers as Raman excitation sources can result in significant analyte Raman signal confounding due to spectral nonlinear and thermal phenomena.…”

Section: Introductionmentioning

confidence: 99%

“…10 Time-gating was successfully used by many research groups in their standoff Raman instruments. 11–15…”

Section: Introductionmentioning

confidence: 99%

Standoff Deep Ultraviolet Raman Spectrometer for Trace Detection

Bykov,

Asher

2024

Appl Spectrosc

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We developed a state-of-the-art, high-sensitivity, low-stray-light standoff deep-ultraviolet (DUV) Raman spectrometer for the trace detection of resonance Raman-enhanced chemical species. As an excitation source for Raman measurements, we utilized our recently developed, second-generation, miniaturized, diode-pumped, solid-state neodymium-doped gadolinium orthovanadate (Nd:GdVO4) laser that generates quasi-continuous wave 228 nm light. This 228 nm excitation enhances the Raman intensities of vibrations of NOx groups in explosive molecules, aromatic groups in biological molecules, and various aromatic hydrocarbons. Our DUV Raman spectrograph utilizes a custom DUV f/8 Cassegrain telescope with an ∼200 mm diameter primary mirror, high-efficiency DUV transmission gratings, custom DUV mirrors, and a custom 228 nm Rayleigh rejection filter. We utilized our new standoff DUV Raman spectrometer to measure high signal-to-noise ratio spectra of ∼50 μg/cm2 drop-cast explosives: ammonium nitrate (AN), trinitrotoluene, pentaerythritol tetranitrate as well as aromatic biological molecules: lysozyme, tryptophan, tyrosine, deoxycytidine monophosphate, deoxyadenosine monophosphate at an ∼3 m distance within 10–30 s accumulation times. We roughly estimate the average ultraviolet resonance Raman (UVRR) detection limits for the relatively homogeneous drop-cast films of explosives and biological molecules to be ∼1 μg/cm2 when utilizing a continuous raster scanning that averages Raman signal over ∼1 cm2 sample area to avoid quick analyte depletion due to ultraviolet (UV) photolysis. We determined 3 m standoff UVRR detection limits for drop-cast AN films and identified factors impacting UVRR detection limits such as analyte photochemistry and analyte morphology. We found a detection limit of ∼0.5 μg/cm2 for drop-cast AN films on glass substrates when the Raman signal is averaged over ∼0.5 cm2 of sample surface using a continuous raster scan. For a step raster scan, when the probed sample area is limited to the laser spot size, the detection limit is approximately tenfold higher (∼5 μg/cm2) due to the impact of UV photochemistry.

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