Light Source
A light source includes a mode-locked laser; a beam splitter that branches the femtosecond optical pulse train; a CW solid-state laser; a first beam combiner that outputs one side of the femtosecond optical pulse train on the same axis; a secondary nonlinear optical element that outputs a difference frequency generation and conversion optical pulse train from either a continuous wave or a femtosecond optical pulse train; an amplifier that amplifies the difference frequency generation and conversion optical pulse train; a polarization-maintaining all normal dispersion high nonlinear fiber that converts the other femtosecond optical pulse train into a supercontinuum optical pulse train; a first dispersion medium that converts the supercontinuum optical pulse train into a pulse width that is approximately the same as the difference frequency generation and conversion optical pulse train; and a second beam combiner that multiplexes and outputs the difference frequency generation and conversion optical pulse train and the supercontinuum optical pulse train.
1 . A light source for Raman scattering spectroscopy comprising:
a mode-locked laser that outputs a femtosecond optical pulse train of a center λ s ;
a beam splitter that branches the femtosecond optical pulse train into two systems of a first femtosecond optical pulse train and a second femtosecond optical pulse train, in terms of power;
a continuous wave oscillation solid-state laser that outputs continuous wave;
a first beam combiner that transmits the continuous wave output from the continuous wave oscillation solid-state laser, reflects the first femtosecond optical pulse train, and outputs the continuous wave and the first femtosecond optical pulse train on the same axis;
a secondary nonlinear optical element that includes at least one conversion element for outputting a difference frequency generation and conversion optical pulse train including a picosecond optical pulses of a center λ c , by generating a difference frequency between the continuous wave and the first femtosecond optical pulse train;
an amplifier that amplifies the difference frequency generation and conversion optical pulse train;
a polarization-maintaining all normal dispersion high nonlinear fiber that converts the second femtosecond optical pulse train into a supercontinuum optical pulse train;
a first dispersion medium that converts the supercontinuum light pulse train into a pulse width that is approximately the same as a pulse width of the difference frequency generation and conversion optical pulse train output from the amplifier; and
a second beam combiner that multiplexes and outputs the difference frequency generation and conversion optical pulse train output from the amplifier and the supercontinuum optical pulse train output from the first dispersion medium,
wherein a center λ s and a center λ c are set so that coherent anti-Stokes Raman scattering measurement is performed by the difference frequency generation and conversion optical pulse train and the supercontinuum optical pulse train output from the amplifier.
2 . The light source according to claim 1 , wherein the secondary nonlinear optical element further comprises:
a plurality of the conversion elements having different lengths; and,
a switch mechanism that is installed on an input side of the plurality of conversion elements to guide input light to a specific conversion element.
3 . The light source according to claim 1 , further comprising:
a second dispersion medium that is disposed between the secondary nonlinear optical element and the amplifier to extend a pulse width, by applying a chirp to the difference frequency generation and conversion optical pulse train that is output from the secondary nonlinear optical element.
4 . The light source according to claim 1 , wherein the laser medium of the mode-locked laser is one of Cr 4+ : YAG, Cr forsterite, Ti sapphire, Cr: LiSAF, Cr: LiCAF, Cr: ZnSe, Cr: ZnS, or YAG, YVO 4 or glass (bulk and fiber) added with one rare earth ion selected from Yb, Er, Nd, Tm, and Ho, or a semiconductor crystal.
5 . The light source according to claim 1 , wherein a shape of a gain medium constituting the mode-locked laser is any one of a rod, a disk or a fiber.
6 . The light source according to claim 1 , wherein the amplifier is one of a glass fiber amplifier added with one rare earth ion selected from Yb, Er, Nd, Tm, Ho, etc., or a single crystal fiber amplifier wherein one rare earth ion selected from Yb, Er, Nd, Tm, Ho, or the like is added to a part.
7 . The light source according to claim 1 , wherein the continuous wave oscillation solid-state laser is any one of a glass fiber laser, a bulk-shaped single crystal laser, a bulk-shaped ceramic laser, a waveguide-type single crystal laser, a waveguide-type ceramic laser, or a semiconductor laser.
8 . The light source according to claim 1 , wherein the conversion element included in the secondary nonlinear optical element is any one of a periodically poled lithium niobate, a periodically poled lithium tantalate, and a periodically poled KTP crystal.