Long propagating velocity-controlled Einstein's mirror for terahertz light conversion.

Area of Science:

• Nonlinear optics
• Laser physics
• Terahertz (THz) science and technology

Background:

• Einstein's relativistic mirror concept offers unique wave interaction possibilities.
• Controlling the velocity and properties of such mirrors is crucial for practical applications.
• Existing methods for manipulating THz pulses often have limitations in efficiency or control.

Purpose of the Study:

• To implement Einstein's relativistic mirror with controllable velocity and long propagation distance.
• To investigate the use of dense free carrier fronts generated by multiphoton absorption as relativistic mirrors.
• To demonstrate the application of these relativistic mirrors for efficient terahertz pulse conversion.

Main Methods:

• Generating dense free carrier fronts via multiphoton absorption of tilted-pulse-front femtosecond laser pulses in dielectric or semiconductor media.
• Controlling the propagation velocity of the carrier front by adjusting the pulse front tilt angle.
• Simulating the interaction of terahertz pulses with these generated relativistic mirrors.

Main Results:

• Successfully implemented a relativistic mirror with controllable velocity and long propagation distance.
• Demonstrated that the generated carrier fronts act as efficient Doppler-type converters for terahertz pulses.
• Observed significant pulse compression (over an order of magnitude) and spectrum broadening of reflected terahertz pulses without noticeable amplitude change, particularly using three-photon absorption in ZnS.

Conclusions:

• The proposed technique effectively creates a controllable relativistic mirror using femtosecond laser-induced carrier fronts.
• This method provides a powerful new tool for manipulating terahertz pulses, enabling significant compression and spectral broadening.
• The findings open avenues for converting strong low-frequency terahertz pulses for diverse scientific and technological applications.