Abstract
The detection of peaks shifts in Raman spectroscopy enables a fingerprint reconstruction to discriminate among molecules with neither labelling nor sample preparation. Time-resolved Raman spectroscopy is an effective technique to reject the strong fluorescence background that profits from the time scale difference in the two responses: Raman photons are scattered almost instantaneously while fluorescence shows a nanoseconds time constant decay. The combination of short laser pulses with time-gated detectors enables the collection of only those photons synchronous with the pulse, thus rejecting fluorescent ones. This review addresses time-gating issues from the sensor standpoint and identifies single photon avalanche diode (SPAD) arrays as the most suitable single-photon detectors to be rapidly and precisely time-gated without bulky, complex, or expensive setups. At first, we discuss the requirements for ideal Raman SPAD arrays, particularly focusing on the design guidelines for optimized on-chip processing electronics. Then we present some existing SPAD-based architectures, featuring specific operation modes which can be usefully exploited for Raman spectroscopy. Finally, we highlight key aspects for future ultrafast Raman platforms and highly integrated sensors capable of undistorted identification of Raman peaks across many pixels.
Highlights
Raman spectroscopy is a non-destructive technique which provides information on the physical and chemical structure of a material, based on the interaction of molecule vibrational modes with light
We will present an overview of the physical phenomena at the basis of Raman effect, and we will focus on Raman spectroscopy, discussing setup requirements and Raman-fluorescence trade-offs
It consists of an inelastic scattering of incident light photons that involves generating new frequencies during the light-matter interaction. These new frequencies are related to the vibrational and rotational modes of the analyte under observation [14]. Since these modes are a unique feature of each single molecule, Raman spectroscopy is a powerful tool to investigate molecular specificity and structure features
Summary
Raman spectroscopy is a non-destructive technique which provides information on the physical and chemical structure of a material, based on the interaction of molecule vibrational modes with light. It is used in many scientific fields, such as medicine [1,2,3], geology and mineralogy [4,5], pharmaceuticals [6,7,8], and planetary science for the identification and characterization of unknown samples [9,10,11]. One of its greatest advantages is the label-free operation, which avoids any sample preparation and fluorescent marker introduction, making Raman one of the most versatile non-invasive real-time measurement technique
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