Pulsed terahertz radiation due to coherent phonon-polariton excitation in 〈110〉 ZnTe crystal

Abstract

Pulsed terahertz (THz) radiation, generated through optical rectification (OR) by exciting [110] ZnTe crystal with ultrafast optical pulses, typically consists of only a few cycles of electromagnetic field oscillations with a duration about a couple of picoseconds. However, it is possible, under appropriate conditions, to generate a long damped oscillation tail (LDOT) following the main cycles. The LDOT can last tens of picoseconds and its Fourier transform shows a higher and narrower frequency peak than that of the main pulse. We have demonstrated that the generation of the LDOT depends on both the duration of the optical pulse and its central wavelength. Furthermore, we have also performed theoretical calculations based upon the OR effect coupled with the phonon-polariton mode of ZnTe and obtained theoretical THz waveforms in good agreement with our experimental observation.

Ultrafast photoexcitation dynamics of ZnTe crystals by femtosecond optical pump‐probe and terahertz emission spectroscopy

“…A typical Fourier transform of the LDOT as shown in Figure 6B clearly reveals two peaks at 2.6 and 3.7 THz. The 2.6 THz peak is associated with the formation of phonon polariton due to the hybridization of pump‐induced THz radiation and the TO phonon in ZnTe 4,6,8 . We found that the phonon and phonon polariton amplitude both increase linearly with pump power up to 60 mW (corresponding to 120 μJ/cm 2 ), as is shown in Figure 6C.…”

“…Fourier transform of the LDOT shows the central frequency to be at 2.36 THz, which is noticeably lower than previously determined using OPOP (Figures 6 and 7). In a previous report using OPTE, the phonon polariton frequency is found to be between 1.9 and 2.7 THz, depending on the central frequency and the pulse duration of the pump beam 6 . More specifically, 1.9 THz (2.7 THz) corresponds to 800 nm (750 nm) pump.…”

“…THz radiation produced through optical rectification by irradiating <110> ZnTe with ultrafast optical pulses usually only consists of few‐cycle electromagnetic oscillations about few picoseconds long. However, LDOT can be generated due to the phonon polariton launched by the hybridization of THz radiation and the TO phonon of similar frequency in ZnTe 6 . In this part, we use the same ZnTe crystal as the THz generator in a typical OPTE setup (Figure 1C).…”

“…The wide bandgap semiconductor ZnTe is widely employed as both the detection and generation medium in terahertz‐related optical and spectroscopy setups 1 . Due to its wide applications, the ultrafast dynamics and origin of the coherent phonons in ZnTe have been intensely studied and debated over the past decades 2‐9 …”

THz emission from organic cocrystalline salt: 2, 6-diaminopyridinium-4-nitrophenolate-4-nitrophenol

“…Few-cycle terahertz (THz) electromagnetic pulses have attracted much attention because they have high potential in fundamental studies and practical applications [1]. Inorganic crystals, such as ZnTe, GaSe:Te, used as THz emitters equipped with ultrafast lasers have become popular and high signal-to-noise ratio tabletop THz sources around the world [2][3][4][5]. Recently, intense THz pulses have been demonstrated in LiNbO 3 by using tilted pulse front excitation, which has extended the applications of THz radiation into the nonlinear region [6,7].…”