Programme

O.5 -- Oral, VCTP-47

Date: Tuesday, 2 August 2022

Time: 11:10 - 11:35

Extracting terahertz time domain using high-order harmonic generation

Doan-An Trieu (1), Quan-Hao Truong (1), Thanh-Tu Nguyen (1), Hien T. Nguyen (2), Cam-Tu Le (3,4), DinhDuy Vu (1), Ngoc-Loan Phan (1), and Van-Hoang Le (1)

(1) Computational Physics Laboratory K002, Department of Physics, Ho Chi Minh City University of Education, Ho Chi Minh City 72711, Vietnam. (2) Tay Nguyen University, Buon Ma Thuot City 63161, Vietnam. (3) Atomic Molecular and Optical Physics Research Group, Advanced Institute of Materials Science, Ton Duc Thang University, Ho Chi Minh City 72912, Vietnam. (4) Faculty of Applied Sciences, Ton Duc Thang University, Ho Chi Minh City, 72912, Vietnam

Used to be a gap in electromagnetic spectrum, terahertz (THz) radiation overcame the limits in generation, and being deploited strongly for many applications. As the results, the waveform of THz radiation, i.e. the temporal electric field, plays an important role. In common, the THz waveform is probed by time-domain spectroscopy (TDS). Based on the pump-probe idea, many current methods for THz-TDS treat THz wave as the pump, and the probe can be either a THz or an infrared pulse. Remarkably, all of these methods use lattices as the interacting environment, which may lead to some unexpected effects, such as, phonon absorption, over-rotation, and so on. For this reason, gas is a potential candidate. In this report, we propose a method to extract the time domain using the high-order harmonic generation (HHG) emitted by the atoms in a combination of an infrared intense laser pulse and a THz pulse. HHG can be simply understood as the emission of photons with frequency of a multiple number of incident laser’s frequency. On the contrary to the symmetric laser-target system, whose HHG contains only odd harmonics, the HHG of this system adds the even ones due to the symmetry breaking caused by the THz pulse. It suggests utilizing the even harmonics, in particular, the even-to-odd ratio (the ratio between intensities of even harmonics and the adjacent odd one) to probe the electric field of the THz pulse. To achieve this goal, we generate HHG by numerically solving the time-dependent Schrödinger equation of atoms in the combined infrared and THz laser pulses. Investigating comprehensively the HHG from different targets and laser pulses, we find out an universal one-to-one dependence of the even-to-odd ratio on the THz's electric field. The analytical expression describing this universal law is performed by the quantum orbit theory. Finally, we use the even-to-odd ratio as a tool to extract the THz time domain. The accuracy and validation of the method is also discussed in detail.

Presenter: Trieu Doan An