Accelerating superluminal laser focus generated by a long-focal-depth mirror with high numerical aperture

Area of Science:

• Optics and Photonics
• Laser Physics

Background:

• Long-focal-depth mirrors offer wavelength independence and high damage thresholds, ideal for focusing intense, broadband ultrashort laser pulses.
• Previous studies on these mirrors were limited to low numerical apertures (NA).

Purpose of the Study:

• To investigate the focusing properties of long-focal-depth mirrors at high NA.
• To explore the generation of accelerating superluminal laser foci and their characteristics.

Main Methods:

• Extended theoretical analysis to high NA conditions.
• Utilized Richards-Wolf integrals to analyze intensity distributions for various incident light polarizations and pulse types.
• Performed numerical simulations to compare focusing properties.

Main Results:

• Confirmed the generation of accelerating superluminal laser foci at high NA, with acceleration increasing with NA.
• Observed focus velocities increasing approximately linearly from c to 1.6c for NA = 0.707.
• Demonstrated that different incident light conditions (polarization, spiral phase, ultrashort pulses) produce distinct intensity distributions and can generate structured foci like hollow conical beams.

Conclusions:

• High NA significantly enhances the accelerating properties of long-focal-depth mirrors.
• The ability to generate structured accelerating superluminal foci opens new application possibilities.