Abstract
Intense terahertz-wave emission in the higher frequency region can result in various applications such as terahertz spectroscopy and ultrafast data communication. In this study, an increase in terahertz waves by the overlap of exciton states in different quantum wells and spectroscopic demonstration are reported. The excitation energy dependence of signal intensity shows the effect of the overlap. The signals measured under the condition of square dependence of intensity on the excitation power indicate interference with the periods corresponding to the laser energy difference. Furthermore, the absorption coefficient of the transparent sheet is obtained at specific frequency. These results indicate that the generation of intense terahertz waves at various frequencies using excitons is possible and that difference frequency mixing is a useful terahertz-wave source.
Highlights
Various applications of terahertz (THz) waves have been proposed, e.g., gas and virus sensing [1,2,3,4], THz scanners [5,6,7], and ultra-high-speed optical communication [8,9,10]
We focused on THz spectroscopy systems that are based on the difference frequency mixing (DFM) process using two external lasers [14,15]
For the DFM process, the bandwidth and frequency of generated THz waves are decided by the excitation laser spectral widths and energy difference; the DFM process is a good method for the generation of THz waves at various frequencies with fine resolution
Summary
Various applications of terahertz (THz) waves have been proposed, e.g., gas and virus sensing [1,2,3,4], THz scanners [5,6,7], and ultra-high-speed optical communication [8,9,10]. The spectral bandwidth of THz waves and the spectroscopic resolution are strongly related to the laser pulse width, scanning step, and moving length This type of signal is obtained by the time-domain measurement; a Fourier transform is required to obtain information in the frequency domain. The enhancement of THz signal intensity due to DFM by excitation of HH and LH excitons was expected. Two laser beams were combined by an optical fiber coupler, and the combined beam was focused on the sample surface through a hole in the off-axis parabolic mirror by a polymethylpentene lens, which was used to collimate the emitted THz wave. The experimental setups for (e) excitation-power dependence and excitation-energy dependences and (f) Fabry-Perot interferometer for frequency measurement
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