<title>Electromagnetic wave interaction with laser-induced plasmas in GaAs</title>

Abstract

A multigigahertz microwave signal was generated and up-converted in a GaAs substrate coplanar strip line. Two 630-nmwavelength laser pulses-one with a normal wavefront, another with a titled wavefront-were respectively used to generate and frequency up-convert the signal. The relativistic plasma front, induced by the tilted optical wavefront, frequency up-shifts the counter-propagating electromagnetic wave via the Doppler effect. When the speed of the plasma front was about 0.4 times the speed of electromagnetic wave in the coplanar strip lines, the experiments showed that the fall time of a step signal decreased more than 30% after the reflection. Given the bandwidth limitations of the data acquisition system, it is possible that a factor of 2 increase was achieved. A transmission line model was employed to simulate this process. The simulation results were consistent with experimental observations. Using coplanar strip lines on a GaAs substrate for microwave signal compression device has the advantage of a high reflection coefficient, frequency tunability, small laser trigger energy, and all-solid-state construction, making this technique suitable for impulse radar applications.

Coherent, Short-Pulse X-ray Generation via Relativistic Flying Mirrors

“…In semiconductors electron-hole pairs are created by irradiating light whose photon energy is higher than the band gap of the semiconductor. The electron-hole plasma front serves as a moving boundary and thus can reflect incoming long-wavelength radiation [16]. This scheme was later well demonstrated by Bae et al in 2009 [17].…”

Extinction theorem for a temporal gas-plasma boundary

“…Substituting ansatz (3) to equation (16) gives where k = ω/c. Performing the integrals, we arrive at equation (18).…”

“…The oscillatory terms in equation ( 3) are the general solutions of the complementary homogeneous equation. Their amplitudes B ± can be found by using the original integral equation (16). Substituting ansatz (3) to equation (16) and performing the integrals (appendix B) gives…”

“…Their amplitudes B ± can be found by using the original integral equation (16). Substituting ansatz (3) to equation (16) and performing the integrals (appendix B) gives…”

“…An efficient way to create a temporal boundary is to increase rapidly the density of free carriers in a material. This approach was implemented by ionization of gases using strong laser and microwave radiation [12][13][14][15] and by photogeneration of electron-hole pairs in semiconductors [16][17][18][19][20]. Frequency up-conversion of microwave and terahertz radiations was demonstrated.…”