Tunable sub-10-fs ultraviolet pulses generated by achromatic frequency doubling

Area of Science:

• Ultrafast Optics
• Nonlinear Optics
• Laser Physics

Background:

• Generating ultrashort ultraviolet (UV) pulses is crucial for various scientific applications.
• Existing methods often face limitations in pulse duration, bandwidth, and tunability.
• Noncollinear optical parametric amplifiers (NOPAs) offer a promising platform for UV pulse generation.

Purpose of the Study:

• To develop a method for generating tunable UV pulses shorter than 10 femtoseconds (fs).
• To significantly enhance the spectral bandwidth of UV pulses.
• To achieve high conversion efficiency in the UV generation process.

Main Methods:

• Achromatic frequency doubling of a noncollinear optical parametric amplifier (NOPA).
• Utilizing a two-prism sequence for first- and second-order achromatic phase matching.
• Employing a beta-barium borate (BBO) crystal for spectral broadening.
• Characterization using zero-additional-phase spectral phase interferometry for direct electric-field reconstruction (ZAP-SPIDER).
• Pulse shaping using a deformable mirror to control higher-order chirp.

Main Results:

• Generation of tunable UV pulses with durations shorter than 10 fs.
• Increased the natural bandwidth of the nonlinear crystal by a factor of 80.
• Achieved extremely broad UV spectra with a Fourier transform limit of 2.9 fs.
• Obtained a conversion efficiency of 20% in a 360-microm-thick BBO crystal.
• Demonstrated generation of 7 fs pulses by controlling higher-order chirp.

Conclusions:

• Achromatic frequency doubling of NOPAs is an effective method for generating ultrashort UV pulses.
• The developed technique significantly broadens UV spectra and enables femtosecond pulse generation.
• The ability to control pulse chirp with deformable mirrors allows for further pulse compression.