Excimer laser and hollow fiber create UV lines for ultrashort-pulse generation

If enough narrow spectral lines are spaced properly in frequency, the result is a periodic series of isolated pulses; this technique can be used to create ultrafast pulses. Researchers at the National Institute of Advanced Industrial Science and Technology (Ibaraki, Japan) and the Lebedev Physical Institute (Moscow, Russia) are using a krypton fluoride excimer laser and a quartz hollow fiber filled with deuterium to create the proper spectra to potentially create trains of 1 fs pulses.

A portion of the 248 nm output from the excimer laser is Stokes-shifted to 249.1 nm in a Raman cell; both wavelengths are then amplified and focused into the fiber, which is 30 cm long and 124 µm in diameter. At a 30 kPa gas pressure, the result is 50 Raman spectral lines in the 230-to-290 nm range, 34 of them with an intensity within 10% of the strongest line (boosting the pressure to 60 kPa results in almost 300 lines in the 220-to-600 nm range). Proper phase control of the Raman spectral lines should result in 1 fs pulses. Contact Leonid Losev at [email protected].