Exploiting Laser-driven Plasma Chemistry for Ultra-high Repetition Rate Nonlinear Optics

Nonlinear optical methods play a crucial role in science and technology and enables scientists across the globe to manipulate light at will and access the entire electromagnetic spectrum, from X-rays to Terahertz (THz) waves via frequency conversion.

Accessing material nonlinearities requires high input light intensity, thus novel laser sources are instrumental in advancing nonlinear optics (NLO).

The first revolution in NLO was enabled by wide access to femtosecond (fs-) laser sources, that ensured sufficiently high peak powers from table-top systems to access most material nonlinearities.

However, these high-peak powers are usually generated at low repetition rates below 1kHz, due to laser source limitations in average power.

In this case, the material nonlinearity recovers by the time the next pulse in the train arrives and every pulse sees the “same” material.

EXPLORE proposes that the second revolution will be the use of high-repetition rate pulses to collectively tailor the nonlinear properties of the medium and allow for the same interactions at greatly reduced energy, thus opening the door to highly NLO at very high repetition rates without prohibitively increasing complexity, with wide implications across disciplines making use of secondary sources of radiation and nonlinear optical methods.

EXPLORE aims to demonstrate this breakthrough idea by using advanced high-power and high-repetition rate laser technology to significantly enhance the nonlinear response of atmospheric plasmas by driving it at ultra-high repetition rates >10 MHz.

In these conditions the air plasma chemical composition does not recover from pulse to pulse and a rich chemical mixture can be tailored to enhance the nonlinear properties such that much lower peak power is required for the nonlinear interaction.

To prove our theory, we will apply the concept to demonstrate a high repetition rate watt-level air-plasma based Terahertz time-domain spectrometer with unprecedented performance.