Phase-matched frequency conversion below 150 nm in KBe₂BO₃F₂.

Area of Science:

• Nonlinear Optics
• Solid-State Physics
• Laser Spectroscopy

Background:

• Sum frequency mixing (SFM) is a nonlinear optical process used to generate new frequencies.
• Generating deep ultraviolet (DUV) light below 150 nm is challenging due to material limitations and phase-matching difficulties.

Purpose of the Study:

• To demonstrate sum frequency mixing (SFM) below 150 nm in KBeBO3F2 crystals.
• To achieve the shortest wavelength generated by phase matching in nonlinear crystals.
• To investigate the optical properties and phase-matching characteristics of KBeBO3F2 for DUV generation.

Main Methods:

• Utilized a 6 kHz Ti:sapphire laser system, employing the fundamental and its fourth harmonic.
• Performed sum frequency mixing experiments in KBeBO3F2 nonlinear crystals.
• Measured output powers, wavelengths, and phase-matching angles.
• Analyzed crystal transmission spectra.

Main Results:

• Successfully demonstrated SFM with a shortest wavelength of 149.8 nm in KBeBO3F2.
• Achieved output powers of 3.6 μW at 149.8 nm and 110 μW at 154.0 nm.
• Observed phase-matching angles deviating by 3-4 degrees from predictions, suggesting a need for updated Sellmeier equations.
• Confirmed crystal transmission supports DUV coherent radiation generation.

Conclusions:

• KBeBO3F2 is a promising nonlinear crystal for generating deep ultraviolet coherent radiation below 150 nm.
• The experimental results highlight the potential for achieving record-shortest wavelengths using this material.
• Further research is needed to refine Sellmeier equations for accurate phase-matching predictions in KBeBO3F2.