【研究成果】2012

研究成果55

Stimulated Raman hyperspectral imaging based on spectral filtering of broadband fiber laser pulses
Yasuyuki Ozeki, Wataru Umemura, Kazuhiko Sumimura, Norihiko Nishizawa, Kiichi Fukui, and Kazuyoshi Itoh
6.Optics Letters, Vol. 37, Issue 3, pp. 431-433 (2012)

When the optical frequency difference of the two-color laser pulses, the one of which with high-frequency is intensity modulated, matches the vibrational frequency of the sample molecules, the optical energy of the high-frequency pulse is transferred to the low-frequency pulse and to molecular vibrations through the stimulated Raman scattering (SRS) process. The intensity modulation transferred to the other pulse is measured by the lock-in detection technique. We have developed a high-resolution tunable bandpass filter (TBPF) that can be controlled quickly by a galvanometer mirror and applied it to spectral filtering of broadband Yb fiber laser pulses. After optical amplification, we succeeded in obtaining narrowband pulses with a tunability of >225 cm^-1 and a spectral width of <3.3 cm^-1. These pulses were used along with picosecond Ti:sapphire pulses to demonstrate hyperspectral imaging of polymer beads in SRS microscopy. The present approach is advantageous in terms of the high tuning speed and the high spectral resolution, and will be useful for high-speed hyperspectral SRS imaging. The wavelength tunability may be extended up to 500 cm^-1 by further optimization. Moreover, the use of multiple-wavelength pump pulses, which can be generated by fiber-based laser sources, would enable us to acquire SRS signals in different vibrational regions simultaneously.

Results of hyperspectral imaging of PS beads and PMMA beads. Scale bar, 10 μm. (a)-(d) SRS images of different wavenumbers. (e) SRS spectra of PS and PMMA reconstructed from the SRS images.