Coherent Anti-Stokes Raman Holography for Chemically Selective Single-Shot Nonscanning 3D Imaging

We propose and develop a new way for nonscanning coherent anti-Stokes Raman scattering (CARS) imaging by using CARS holography, which can capture, at a single shot, both the amplitude and the phase of a coherent Raman image. It hence allows for chemically selective three-dimensional imaging at a laser pulse duration limited speed, which is not possible to achieve by using any of the existing laser scanning based Raman imaging techniques. We have demonstrated single-shot (pulse duration: $\sim 5\mathrm{ns}$) holographic CARS imaging of microspheres. Our results show that coherent anti-Stokes Raman holography can open a new path for nonscanning label-free imaging.

Figure 1

(a) Schematic diagram illustrating the principle of coherent anti-Stokes Raman holography, (b) Schematic diagram of the experimental setup. L1: singlet lens, focal length 750 mm, L2: singlet lens, focal length 150 mm, L3: long working distance objective lens, focal length 10 mm, L4: singlet lens, focal length 300 mm or 500 mm, F: band-pass filter, BS: pellicle beam splitter. (c) A typical hologram recorded on a CCD camera by interfering a single pair of reference pulse and signal pulse generated by FWM in index oil. (d) Dependence of CARS signal on the power of the pump beam in logarithmic scale.

Figure 2

Chemical selective CARS holographic imaging. (a) single-shot CARS hologram recorded at polystyrene resonance wavelength; (b) single-shot hologram recorded at PMMA resonance wavelength; (c) reconstructed CARS intensity image from the hologram shown in (a); (d) reconstructed CARS intensity image from the hologram shown in (b).

Figure 3

Holographic CARS imaging of multiple polystyrene microspheres suspended in water. (a): recorded single-shot CARS hologram; (b): reconstructed CARS intensity image (without diffraction compensation); (c): reconstructed CARS phase image (without diffraction compensation); (d)–(g): intensity distribution of digitally propagated CARS field at different planes; from (d) to (g): $z=7.92\mu \mathrm{m}$, $2.92\mu \mathrm{m}$, $-15.6\mu \mathrm{m}$, $-20.6\mu \mathrm{m}$, respectively; (h): calculated CARS intensity distribution of a single $10\mathrm{\text{−}}\mu \mathrm{m}$-diameter microsphere at a distance of $5\mu \mathrm{m}$ away from the exit plane by using the beam propagation method; it is shown that the generated CARS field is focused by the microsphere to result in a much smaller spot size.