Abstract
In the first section of this Chapter, the basics of nonlinear optical (NLO) processes are systematically described. Then the generation of the visible pulse utilizing the NLO processes is described and ultrafast spectroscopy using the visible pulse is discussed. By using such short pulse, fast chemical reactions, which cannot be identified by utilizing strobe light or flash lamp, can be studied. After the development of femtosecond lasers, they have been widely applied to observe the transition state of various chemical reactions. In the near infrared (NIR) region, a commercial light source of Ti:sapphire laser is available as a femtosecond light source, but not available in the visible and ultraviolet (UV) regions. In this article, we report our development of sub 10 fs visible-NIR, UV, and deep-ultraviolet (DUV) pulses and their applications to ultrafast spectroscopy.
Highlights
In the first section of this Chapter, the basics of nonlinear optical (NLO) processes are systematically described
optical parametric fluorescence (OPF) and optical parametric generation (OPG) are sometimes referred to as spontaneous parametric down-conversion (SPDC), especially when the two generated photons degenerate in frequency
We have developed a method called non-collinear optical parametric amplification (NOPA) [16,17,18], which is described below
Summary
We would like to briefly introduce nonlinear optics in a way that differs slightly from that used by most textbooks in wide circulation. In an OPA process, an intense pump beam amplifies a weak signal without real population inversion In this case, conservation of energy is satisfied among the pump photon of frequency (angular frequency, hereafter referred as frequency in many cases) ω p , the signal photon of frequency ω s , and an idler photon of frequency ω i = ω p − ω s , which is generated simultaneously through the second-order nonlinear polarization. We used OPA, which is a widely used method to amplify light; its gain bandwidth is insufficient to amplify the visible broadband spectrum for generating ultrashort pulses as short as 10 fs To solve this problem, we have developed a method called non-collinear optical parametric amplification (NOPA) [16,17,18], which is described below. The pulse duration was estimated to be 10 fs from the measured SHG-
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