Strong enhancement of terahertz radiation from semiconductor surfaces using MgO hemispherical lens coupler

Abstract

We report an enhancement of terahertz radiation power from InAs surfaces excited by ultrashort laser pulses using an MgO hemispherical lens coupler. The power of the terahertz radiation from the InAs surface with the MgO lens coupler is 50 times larger than that from the InAs surface without the MgO lens coupler. The enhancement is explained mainly by the increase of the transmission efficiency of the THz wave from InAs to free space.

Photoconductive Emission and Detection of Terahertz Pulsed Radiation Using Semiconductors and Semiconductor Devices

“…This can be explained by the effect of the coupling lens leading to a more efficient collection of the lower-frequency components, otherwise lost by diffraction. A similar frequency shift has been reported for THz emission from InAs with a MgO lens in a reflection geometry setup [38] and also for THz emission from InAs thin films with a Si lens in transmission geometry [39]. Figure 7 shows the magnetic field dependence of the peak signal of the THz-TDS waveform emitted from n-type InSb without a coupling lens (note that the THz emission efficiency and the magnetic field dependence with n-type InSb are similar to those of p-type InSb).…”

“…Aside from their simplicity and robustness, one of the advantages of these semiconductors as THz emitters is their compatibility with 1.55-μm laser sources. InAs has exhibited significant THz emission enhancement by an applied magnetic field, [36] as well as by using a surface coupling prism or lens [37][38][39]. On the other hand, InSb has been not been thoroughly investigated for similar enhancement studies.…”

Terahertz Emission Enhancement in InAs Thin Films Using a Silicon Lens Coupler

“…The frequency shift is similarly reported in a reflection geometry setup using an MgO lens on a bare InAs wafer. 20) As has been previously reported, the conversion efficiency of photoconductive antennas is around 2 Â 10 À5 . 30) In contrast, the reported conversion efficiency for bare InAs ranges between 10 À6 to 10 À7 .…”

Terahertz emission from indium oxide films on MgO substrates excited at a photon energy below the bandgap

“…However, few studies are made on In 2 O 3 growth on MgO, wherein a huge lattice mismatch can influence the film's properties [6]. Magnesium oxide is so chosen due to its excellent transmission properties both in the optical and THz-frequency regimes [7]. Results show that even at an excitation photon energy lower than the bandgap, the In 2 O 3 film exhibited THz emission.…”