High-field half-cycle terahertz radiation from relativistic laser interaction with thin solid targets

Abstract

This version is available at https://strathprints.strath.ac.uk/49262/ Strathprints is designed to allow users to access the research output of the University of Strathclyde. Unless otherwise explicitly stated on the manuscript, Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Please check the manuscript for details of any other licences that may have been applied. You may not engage in further distribution of the material for any profitmaking activities or any commercial gain. You may freely distribute both the url (https://strathprints.strath.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge.Any correspondence concerning this service should be sent to the AbstractIt is found that half-cycle terahertz (THz) pulses with the peak field over 100MV/cm can be produced in ultrashort intense laser interactions with a thin solid target. These THz pulses are shown to emit from both the front and rear sides of the solid target and are attributed to the coherent transition radiation (CTR) by laserproduced ultrashort fast electron bunches. After the primary THz pulses, subsequent secondary half-cycle pulses are generated while some refluxing electrons cross the vacuum-target interfaces. Since such strong THz radiation is well synchronized with the driving lasers, it is particularly suitable for applications in various pump-probe experiments.

Demonstration of Coherent Terahertz Transition Radiation from Relativistic Laser-Solid Interactions

“…However, they do not apply here. Since the forward fast electron beam can pass through the solid rear surface, the transition radiation could be responsible for the observed THz radiation from the rear surface [20]. According to the model of transition radiation [13], the wavelength range λ of coherent transition radiation is predicted to be σ ez <λ<ρ/ − 1, where σ ez is the longitudinal length of 6 electron beams, ρ the target size, and γ the relativistic Lorentz factor, respectively.…”

“…If the radiation was generated by ITR, N e had to be as huge as 1.75×10 20 to match the measured THz energy. This number is unreasonable according to the well-known conversion efficiency from the laser energy to the fast electrons.…”

“…Since the THz yield is found to be correlated with the square of the proton number, it is attributed to a transient dipole-like charge distribution structure formed by target normal sheath acceleration (TNSA), referred to hereafter as TNSA radiation [18]. On the other hand, in principle, THz radiation can be produced efficiently via the transition radiation process at the rear surface of a laser-irradiated thin solid foil [20], since both the short electron bunch duration and high bunch charge are ideal for this mechanism. Previous studies on the transition radiation from solid targets mainly concern in the optical region [21,22].…”

Effects of target pre-heating and expansion on terahertz radiation production from intense laser-solid interactions

“…It therefore appears that the contribution of THz emission due to this mechanism is less important. As discussed above, other THz generation mechanisms are associated with energetic electron production, such as the surface transient current at the front [3] or rear [22] , antenna emission [2] , and transient radiation [23][24][25] , which occur when the preplasma has moderate-to-short density scale lengths. Generally, all of these mechanisms depend upon the preplasma conditions in two ways, by changing (1) the absorption of laser energy to fast electrons, and (2) the injection properties of the fastelectron distribution (see reference [26] for an example study of the sensitivity to preplasma scale length).…”

Below gap optical absorption in GaAs driven by intense, single-cycle coherent transition radiation

“…Laser-based sources have enabled pulses with peak fields of order 1 MV/cm and energies of ~10-100 μJ at frequencies near 1 THz [1][2][3][4][5][6][7][8][9]. Nevertheless, many field-driven processes remain out of reach at these field strengths, and accelerator based sources, based on coherent radiation from relativistic electron beams, represent an alternative pathway towards the generation of extreme fields, reaching sizable fractions of interatomic fields in matter [10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Previously, we have reported the measurement of quasi-half cycle pulses with peak fields exceeding 20 MV/cm at a center frequency of 10 THz via coherent transition radiation (CTR) at the Linac Coherent Light Source (LCLS) free-electron laser [13,24].…”