Abstract-Terahertz coherent anti-Stokes Raman scattering microscopy

Liqing Ren, Ilan Hurwitz, Dekel Raanan, Patric Oulevey, Dan Oron, and Yaron Silberberg

Fig. 1. THz-CARS scheme. (a) Principle of THz-CARS microscopy. ENF, excitation notch filter; ULPF, ultra-steep long-pass filter; USPF, ultra-steep short-pass filter. (b) Schematic of a THz-CARS microscope. DNF, detection notch filter; BPF, band-pass filter; DM, dichroic mirror; Obj, objective; SPF, short-pass filter. THz-CARS, SHG, FWM, and TPEF signals are collected by corresponding photomultiplier tubes, PMT-C, PMT-S, PMT-F, and PMT-T, respectively.

https://www.osapublishing.org/optica/abstract.cfm?uri=optica-6-1-52

Vibrational spectroscopic imaging is useful and important in biological and medical studies. Yet, vibrational imaging in the terahertz region (<300  cm−1$<300{\mathrm{cm}}^{-1}$) under biologically relevant conditions is currently unavailable, as none of the available methods possesses a sufficient sensitivity and high spatial resolution at the same time. Here, we develop a terahertz coherent anti-Stokes Raman scattering (THz-CARS) microscope with a high sensitivity and high spatial resolution that shows chemically selective imaging of biological tissues by using low-frequency collective modes of the corresponding constituents, filling the existing energy scale gap for vibrational imaging in the THz region. The observation of collective modes of biomacromolecules, such as collagen and non-collagenous proteins, may have significant implications for elucidating their corresponding biological functions, and the methodology presented may find wider applications in biomedical research.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Impulsive Raman spectroscopy via precision measurement of frequency shift with low energy excitation

Dekel Raanan, Liqing Ren, Dan Oron, and Yaron Silberberg

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-43-3-470&origin=search

Stimulated Raman scattering (SRS) has recently become useful for chemically selective bioimaging. It is usually measured via modulation transfer from the pump beam to the Stokes beam. Impulsive stimulated Raman spectroscopy, on the other hand, relies on the spectral shift of ultrashort pulses as they propagate in a Raman active sample. This method was considered impractical with low energy pulses since the observed shifts are very small compared to the excitation pulse bandwidth, spanning many terahertz. Here we present a new apparatus, using tools borrowed from the field of precision measurement, for the detection of low-frequency Raman lines via stimulated-Raman-scattering-induced spectral shifts. This method does not require any spectral filtration and is therefore an excellent candidate to resolve low-lying Raman lines (

<200  cm−1$<200{\mathrm{cm}}^{-1}$), which are commonly masked by the strong Rayleigh scattering peak. Having the advantage of the high repetition rate of the ultrafast oscillator, we reduce the noise level by implementing a lock-in detection scheme with a wavelength shift sensitivity well below 100 fm. This is demonstrated by the measurement of low-frequency Raman lines of various liquid samples.

© 2018 Optical Society of America