Generation of 265-fs millijoule pulses at 1940 nm from a solid-state regenerative amplifier has been demonstrated. The system consists of a thulium-doped fluoride (Tm:ZBLAN) fiber oscillator, a two stage Tm:ZBLAN fiber preamplifier, and a regenerative amplifier with a thermoelectrically cooled thulium-doped yttrium aluminium perovskite crystal. The newly developed light source is used for pumping an ultra broadband mid-infrared optical parametric amplifier based on a gallium selenide crystal. The 2.5–4 μm range of a multioctave supercontinuum, generated in a polarization-maintaining ZBALN fiber, is used as the MIR seed. The amplified signal in combination with the corresponding idler pulses spread from 2.5 to 10 μm in a collinear geometry.
A temperature gradient induced by a focused 2 μm Tm-doped fiber laser is used for opto-thermal trapping of colloidal particles in an aqueous solution. The water has a large absorption peak around 2 μm in wavelength due to its vibrational modes, and some local temperature gradient is generated around the focus where the colloidal particles are migrated when salt is slightly added to the solution. In this study, the experimental results under different salt (electrolyte) concentrations are compared in order to clarify the role of an electrostatic force generated due to ions redistribution in the temperature gradient. As a result, the particles are trapped when the salt concentration is higher than 10 μg/ml, whereas they are not trapped under this concentration. Although a prediction of the electrostatic field near the heat source is difficult, our findings suggest that the mechanism of trapping in our system may ascribe to thermoelectric effect.
Ultraviolet (UV) and vacuum-UV pulses (VUV) were simultaneously generated by using four-wave mixing
through filamentation in neon gas. Second harmonic of Ti:sapphire laser output (400 nm, ωSHG) and near
infrared pulses (1200 nm, ωNIR) from a noncollinear optical parametric amplifier were gently focused into neon
gas, and ultrashort pulses with the center wavelengths of 237 nm (ωfwm) and 167 nm (ωcas) were produced by
four-wave mixing processes ωSHG + ωSHG - ωNIR → ωfwm and ωfwm + ωSHG - ωNIR → ωcas, respectively. The
energy of the generated 237 nm pulse was more than one micro joule. Transfer of spectral phase from the near
infrared ultrashort pulses to the UV pulses through the four-wave mixing process was also demonstrated. The
even order spectral phase of the near infrared pulse was transfered to the UV pulse with the opposite sign,
whereas the odd order spectral phase was transfered with the same sign. A positively chirped near infrared pulse
was used for generating a negatively chirped UV pulse, which was compressed down to 25 fs by a magnesium
fluoride window. In principle, the spectral phase transfer scheme can also be applied to the chirp control of the
generated VUV pulses.
Conference Committee Involvement (1)
Ultrafast Optics 2017
8 October 2017 | Jackson Hole, Wyoming, United States
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