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Wide-Field Detected Fourier Transform CARS Microscopy

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ABSTRACT

We present a wide-field imaging implementation of Fourier transform coherent anti-Stokes Raman scattering (wide-field detected FT-CARS) microscopy capable of acquiring high-contrast label-free but chemically specific images over the full vibrational ‘fingerprint’ region, suitable for a large field of view. Rapid resonant mechanical scanning of the illumination beam coupled with highly sensitive, camera-based detection of the CARS signal allows for fast and direct hyperspectral wide-field image acquisition, while minimizing sample damage. Intrinsic to FT-CARS microscopy, the ability to control the range of time-delays between pump and probe pulses allows for fine tuning of spectral resolution, bandwidth and imaging speed while maintaining full duty cycle. We outline the basic principles of wide-field detected FT-CARS microscopy and demonstrate how it can be used as a sensitive optical probe for chemically specific Raman imaging.

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Wide-field detected FT-CARS microscopy on toluene.(a) Time-independent coherent anti-Stokes background scattering of the scanning region (30 × 30 μm2). The inhomogeneous intensity distribution arises from the harmonic motion of the scanning mirrors. (b) Coherent oscillations of toluene recorded for 3.5 ps on a single pixel (dashed circle in a). The data was recorded in 30 s with an EMCCD camera integration time of 20 ms in the absence of EM gain. (c) Fourier power spectrum of the coherent oscillations in (a) showing the characteristic vibrational peaks of toluene. (d) Fourier power map along the vertical dashed black line in (a). We note, that the Fourier intensity scales quadratically with the incident power (inset).
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f3: Wide-field detected FT-CARS microscopy on toluene.(a) Time-independent coherent anti-Stokes background scattering of the scanning region (30 × 30 μm2). The inhomogeneous intensity distribution arises from the harmonic motion of the scanning mirrors. (b) Coherent oscillations of toluene recorded for 3.5 ps on a single pixel (dashed circle in a). The data was recorded in 30 s with an EMCCD camera integration time of 20 ms in the absence of EM gain. (c) Fourier power spectrum of the coherent oscillations in (a) showing the characteristic vibrational peaks of toluene. (d) Fourier power map along the vertical dashed black line in (a). We note, that the Fourier intensity scales quadratically with the incident power (inset).

Mentions: To demonstrate the concepts behind wide-field detected FT-CARS microscopy we begin by imaging a 30 × 30 μm2 region of toluene. The non-resonant background generated by pump and probe pulses individually is easily detected and allows for rapid alignment of the correct focal plane for the experiment. Without stepping the time delay between the pump and probe pulses (18 fs, 800 nm, 3.6 mW in each interferometer arm), we observe a scanning pattern with a characteristic harmonic oscillator intensity distribution in two dimensions caused by the resonant scanning motion (Fig. 3a). Additionally, phase drift between the resonant SM for short exposure times (<10 ms) causes Lissajous patterns to appear occasionally.


Wide-Field Detected Fourier Transform CARS Microscopy
Wide-field detected FT-CARS microscopy on toluene.(a) Time-independent coherent anti-Stokes background scattering of the scanning region (30 × 30 μm2). The inhomogeneous intensity distribution arises from the harmonic motion of the scanning mirrors. (b) Coherent oscillations of toluene recorded for 3.5 ps on a single pixel (dashed circle in a). The data was recorded in 30 s with an EMCCD camera integration time of 20 ms in the absence of EM gain. (c) Fourier power spectrum of the coherent oscillations in (a) showing the characteristic vibrational peaks of toluene. (d) Fourier power map along the vertical dashed black line in (a). We note, that the Fourier intensity scales quadratically with the incident power (inset).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC5121585&req=5

f3: Wide-field detected FT-CARS microscopy on toluene.(a) Time-independent coherent anti-Stokes background scattering of the scanning region (30 × 30 μm2). The inhomogeneous intensity distribution arises from the harmonic motion of the scanning mirrors. (b) Coherent oscillations of toluene recorded for 3.5 ps on a single pixel (dashed circle in a). The data was recorded in 30 s with an EMCCD camera integration time of 20 ms in the absence of EM gain. (c) Fourier power spectrum of the coherent oscillations in (a) showing the characteristic vibrational peaks of toluene. (d) Fourier power map along the vertical dashed black line in (a). We note, that the Fourier intensity scales quadratically with the incident power (inset).
Mentions: To demonstrate the concepts behind wide-field detected FT-CARS microscopy we begin by imaging a 30 × 30 μm2 region of toluene. The non-resonant background generated by pump and probe pulses individually is easily detected and allows for rapid alignment of the correct focal plane for the experiment. Without stepping the time delay between the pump and probe pulses (18 fs, 800 nm, 3.6 mW in each interferometer arm), we observe a scanning pattern with a characteristic harmonic oscillator intensity distribution in two dimensions caused by the resonant scanning motion (Fig. 3a). Additionally, phase drift between the resonant SM for short exposure times (<10 ms) causes Lissajous patterns to appear occasionally.

View Article: PubMed Central - PubMed

ABSTRACT

We present a wide-field imaging implementation of Fourier transform coherent anti-Stokes Raman scattering (wide-field detected FT-CARS) microscopy capable of acquiring high-contrast label-free but chemically specific images over the full vibrational &lsquo;fingerprint&rsquo; region, suitable for a large field of view. Rapid resonant mechanical scanning of the illumination beam coupled with highly sensitive, camera-based detection of the CARS signal allows for fast and direct hyperspectral wide-field image acquisition, while minimizing sample damage. Intrinsic to FT-CARS microscopy, the ability to control the range of time-delays between pump and probe pulses allows for fine tuning of spectral resolution, bandwidth and imaging speed while maintaining full duty cycle. We outline the basic principles of wide-field detected FT-CARS microscopy and demonstrate how it can be used as a sensitive optical probe for chemically specific Raman imaging.

No MeSH data available.


Related in: MedlinePlus