**5. Sub-diffraction-limited CARS microscopy**

194 Photonic Crystals – Innovative Systems, Lasers and Waveguides

typical molecular vibrational modes for benzonitrile, at the wavenumbers of 1016 cm-1, 2248 cm-1 and 3090 cm-1, are plotted one by one as a function of τ and fitted to equation (4.5) in

> 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

 3090cm-1 Fitting curve T/2 = 0.50ps

**Normalized Intensity (%)**

<sup>0123456</sup> 0.0

**Time (ps)**

Fig. 18. Vibrational dephasing processes and their corresponding dephasing times of various molecular vibrational modes for benzonitrile in benzonitrile-methanol-ethanol mixture solution shown in (a)-(c) respectively, with the solid line corresponding to the variation of CARS signal with delay time and the dash dot line representing the single exponential

From experimental results, the intensities of the CARS signals corresponding to different molecular vibrational modes attenuate exponentially against the delay time in a large dynamic range. By fitting the intensity data of the CARS signal to a single exponential function for the molecular vibrational modes at different wave-numbers, half of vibrational dephasing time T/2 can be worked out as shown in figure 17, which are consistent with the previously published data [43, 121-123]. But in a benzonitrile-methanol-ethanol mixture solution, the experimental results show that the influence of solvent on the property of solute is reflected not by the Raman peak position but by the variations of the vibrational

As discussed above, the simultaneously detectable spectral range of the ultra-broadband T-CARS with SC depends on the quality of the SC. It is of importance to simultaneously obtain the complete molecular vibrational spectra and the dephasing times of various molecular vibrational modes of the sample. The former is very useful for effectively and accurately

<sup>0123456</sup> 0.0

**Time (ps)**

**(b)**

 2248cm-1 Fitting curve T/2 = 0.58ps

figure 18 (a)-(c), respectively.

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

**Normalized Intensity (%)**

fitting curve [84].

<sup>012345678</sup> 0.0

**Time (ps)**

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

dephasing times for different molecular vibrational modes.

**4.4 Simultaneously obtaining the complete molecular vibrational spectra** 

**Normalized Intensity (%)**

**(a)**

 1016cm-1 Fitting curve T/2 = 1.49ps

1.0 **(c)**
