Ultrafast Ultraviolet C and Visible Laser Light with Broadly Tunable Spectrum

Abstract

We demonstrate a versatile technique for generating continuously wavelength-tunable laser waveforms, with mJ pulse energies and ultrashort pulse durations down to few-cycle in the ultraviolet C and visible spectral ranges. Using the processes of self-phase modulation or Raman-induced spectral broadening, we substantially expand the spectrum of a femtosecond 𝟏𝟏𝟏𝟏𝟏𝟏𝟏𝟏 𝒏𝒏𝒏𝒏 𝒀𝒀𝒀𝒀: 𝑪𝑪𝑪𝑪𝑭𝑭𝟐𝟐 laser, allowing for an extensive wavelength-tunability of the second and fourth harmonics of the laser within the visible and ultraviolet C spectral regions at 𝟒𝟒𝟒𝟒𝟏𝟏 − 𝟓𝟓𝟓𝟓𝟏𝟏 𝒏𝒏𝒏𝒏 and 𝟐𝟐𝟏𝟏𝟏𝟏 − 𝟐𝟐𝟐𝟐𝟏𝟏 𝒏𝒏𝒏𝒏 . In addition, our approach exploits nonlinearly assisted self-compression in the second harmonic upconversion of the spectrally broadened infrared pulses with high-order dispersion. This results in 𝟓𝟓 − 𝟏𝟏𝟏𝟏 femtosecond pulses in the visible with an intensity enhancement of up to 𝟏𝟏𝟏𝟏 times. Such an ultrashort visible and ultraviolet C source is ideal for investigating ultrafast dynamics in molecules, solids, and bio and nano systems. Furthermore, this tunable light source enables the generation of bright, narrow-bandwidth, continuously wavelength-tunable, coherent light in the extreme ultraviolet to soft X-ray spectral region. Theoretically, the X-ray pulse structure can consist of sub-𝟐𝟐𝟏𝟏𝟏𝟏 𝑪𝑪𝒂𝒂 pulse trains, making such a source highly suitable for dynamic multidimensional imaging. This includes coherent diffractive imaging of ferromagnetic nanostructures where resonant X-ray scattering is essential, as well as X-ray absorption spectroscopies of advanced quantum materials at pico-nanometer spatial and atto-femtosecond temporal scales.