Efficient deep-hole drilling by a femtosecond, 400 nm second harmonic Ti:Sapphire laser for a fiber optic in-line/pico-liter spectrometer

A second harmonic 400-nm femtosecond laser has demonstrated efficient deep hole drilling for a pico-liter fiber optic spectrometer. A pulse train of 1 kHz with a pulse width of 350 fs and a pulse energy of 15 μJ was irradiated during 1.2 s onto an optical fiber to make a through hole that penetrates the fiber core and works to be a sample cell for a spectroscopic measurement. The spectroscopic measurement is shown using several liquids including dye of rhodamine 6G (R6G). Even with a single cell volume of approximately 20 pico-liter, the absorption spectrum is appeared in the visible range centered at 530 nm depending on the dye concentration. Discussions have also been made on the optimum arrangement of the through hole drilling to obtain sufficient performance of spectroscopic measurements.