Generation of sub-mJ terahertz pulses by optical rectification

Area of Science:

• Optics and Photonics
• Condensed Matter Physics
• Quantum Electronics

Background:

• Optical rectification in lithium niobate is a key method for generating terahertz (THz) radiation.
• Shorter pump pulses (~100 fs) are traditionally used, but theoretical studies suggested longer pulses could enhance efficiency.

Purpose of the Study:

• To experimentally investigate the effect of longer pump pulse durations on THz generation efficiency via optical rectification in lithium niobate.
• To verify theoretical predictions regarding increased THz output with longer pump pulses.

Main Methods:

• Utilized optical rectification in lithium niobate crystals.
• Employed pump pulses with durations significantly longer than conventional ~100 fs pulses, including 1.3 ps.
• Measured THz pulse energy and pump-to-THz energy conversion efficiency.

Main Results:

• Achieved a 2.5x increase in THz pulse energy (125 μJ) using 1.3 ps pump pulses.
• Observed a 2.5x higher pump-to-THz energy conversion efficiency (0.25%) compared to shorter pulses.
• Experimentally verified the predicted advantage of using longer pump pulses for THz generation.

Conclusions:

• Longer pump pulses (e.g., 1.3 ps) significantly enhance THz pulse energy and conversion efficiency in lithium niobate.
• These findings support the potential for generating millijoule-level THz pulses by optimizing crystal cooling and increasing the pumped area.