9 March 2015 Femtosecond pulse laser notch shaping via fiber Bragg grating for the excitation source on the coherent anti-Stokes Raman spectroscopy
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Single-pulse coherently controlled nonlinear Raman spectroscopy is the simplest method among the coherent anti-Stokes Raman spectroscopy systems. In recent research, it has been proven that notch-shaped femtosecond pulse laser can be used to collect the coherent anti-Stokes Raman signals. In this study, we applied a fiber Bragg grating to the notch filtering component on the femtosecond pulse lasers. The experiment was performed incorporating a titanium sapphire femtosecond pulse laser source with a 100 mm length of 780-HP fiber which is inscribed 30 mm of Bragg grating. The fiber Bragg grating has 785 nm Bragg wavelength with 0.9 nm bandwidth. We proved that if the pulse lasers have above a certain level of positive group delay dispersion, it is sufficient to propagate in the fiber Bragg grating without any spectral distortion. After passing through the fiber Bragg grating, the pulse laser is reflected on the chirped mirror for 40 times to make the transform-limited pulse. Finally, the pulse time duration was 37 fs, average power was 50mW, and showed an adequate notch shape. Furthermore, the simulation of third order polarization signal is performed using MATLAB tools and the simulation result shows that spectral characteristic and time duration of the pulse is sufficient to use as an excitation source for single-pulse coherent anti-Stokes Raman spectroscopy. In conclusion, the proposed method is more simple and cost-effective than the methods of previous research which use grating pairs and resonant photonic crystal slab.
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Seung Ryeol Oh, Seung Ryeol Oh, Won Sik Kwon, Won Sik Kwon, Jin Hwan Kim, Jin Hwan Kim, Kyung-Soo Kim, Kyung-Soo Kim, Soohyun Kim, Soohyun Kim, "Femtosecond pulse laser notch shaping via fiber Bragg grating for the excitation source on the coherent anti-Stokes Raman spectroscopy", Proc. SPIE 9355, Frontiers in Ultrafast Optics: Biomedical, Scientific, and Industrial Applications XV, 93550T (9 March 2015); doi: 10.1117/12.2076838; https://doi.org/10.1117/12.2076838

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