Source for ultrafast continuum infrared and terahertz radiation

Area of Science:

• Optics and Photonics
• Laser Physics
• Nonlinear Optics

Background:

• Generating broadband mid-infrared (mid-IR) and terahertz (THz) light is crucial for various spectroscopic applications.
• Existing methods often lack compactness, stability, or sufficient intensity for certain applications.

Purpose of the Study:

• To demonstrate a compact and stable method for generating high-intensity, linearly polarized continuum mid-IR and THz light.
• To utilize nonlinear mixing of ultrafast laser harmonics in air for broadband light generation.

Main Methods:

• Ultrafast femtosecond (fs) laser pulses were used as the primary source.
• Nonlinear mixing of the fundamental, second, and third harmonics of the laser in air via filamentation.
• A compact collinear optical configuration with a delay plate was employed for simplified alignment and enhanced stability.

Main Results:

• Continuous light generation was achieved from <400 cm⁻¹ (12 THz) to >3300 cm⁻¹ (100 THz).
• The generated light is linearly polarized and has high intensity.
• Including the third harmonic in the mixing scheme resulted in a tenfold increase in the generated infrared power.

Conclusions:

• A practical and stable source for generating broadband, high-intensity mid-IR and THz light has been demonstrated.
• The compact design and simplified alignment make this method suitable for widespread adoption.
• This technique is particularly promising for applications in transient infrared spectroscopy.