Terahertz generation from the InP, InSb, GaAs and GaSe crystal surfaces excitated by femtosecond laser pulses has been studied. The terahertz spectra emitted from the native crystals and the crystals previously irradiated by high-energy neutrons or electrons have been recorded. Also, a simulation of the terahertz emission process has been performed. A weak terahertz signal generated from the GaSe native surface has been registered. In the case of electron-irradiated GaSe, the signal is increased several fold because of increased laser radiation absorption. 相似文献
A reflective pulsed terahertz imaging system based on direct detection was developed and used to obtain high-resolution images of a porcine skin specimen with superficial partial-thickness (second-degree) burns. Images were also obtained of the sample through ten layers of dry medical (cotton) gauze with minimal image degradation. The burned and unburned regions of skin had large differences in terahertz reflectivity, displaying clear delineation [20 dB signal-to-noise ratio (SNR) difference signal] between both regions in the images. The terahertz images also exhibited a "halo" surrounding the burn areas that may correlate to the extent of burn injury. The system operated at a center frequency of 500 GHz with 125 GHz of 3 dB bandwidth and used whiskbroom scanning to generate images with a spatial resolution of 1.5 mm. Each pixel was acquired with a 16 ms integration time, resulting in a 40 dB postdetection SNR. The simplicity and high SNR of the reflective terahertz system are promising steps toward real-time terahertz medical imaging. 相似文献
Compact and tunable semiconductor terahertz sources providing direct electrical control, efficient operation at room temperatures and device integration opportunities are of great interest at the present time. One of the most well‐established techniques for terahertz generation utilises photoconductive antennas driven by ultrafast pulsed or dual‐wavelength continuous wave laser systems, though some limitations, such as confined optical wavelength pumping range and thermal breakdown, still exist. The use of quantum dot‐based semiconductor materials, having unique carrier dynamics and material properties, can help to overcome limitations and enable efficient optical‐to‐terahertz signal conversion at room temperatures. Here we discuss the construction of novel and versatile terahertz transceiver systems based on quantum dot semiconductor devices. Configurable, energy‐dependent optical and electronic characteristics of quantum‐dot‐based semiconductors are described, and the resonant response to optical pump wavelength is revealed. Terahertz signal generation and detection at energies that resonantly excite only the implanted quantum dots opens the potential for using compact quantum dot‐based semiconductor lasers as pump sources. Proof‐of‐concept experiments are demonstrated here that show quantum dot‐based samples to have higher optical pump damage thresholds and reduced carrier lifetime with increasing pump power.
The mechanism of the interaction of coherent terahertz radiation with a probe-nanoobject system has been experimentally investigated
in a terahertz apertureless near-field microscope. It has been found that the type of the material of a sample under the probe,
as well as the geometry of the probe, determines the form of the dependence of the differential signal of the terahertz field
on the distance between the probe and sample. The amplitude of the modulation of the probe height significantly affects the
spectral composition of the differential terahertz signal, which is directly related to the amplitude and phase of a terahertz
wave scattered by the probe-nanoobject system. 相似文献
We demonstrated experimentally a terahertz wave modulator based on optically controlled metamaterial. The signal modulation mechanism of the presented terahertz wave modulator was based on the resonance characteristic of metamaterial controlled without or with light excitation. A modulated semiconductor laser with 808 nm wavelength was employed to light the substrate. The interaction between the metamaterial and terahertz wave was strengthened and yielded an appreciable modulation of the terahertz output beam. The modulation speed is 0.1 Kb/s and the modulation depth of the proposed terahertz modulator is about 57% at a frequency of 0.32 THz. 相似文献
Laser-induced plasma acoustic waves are enhanced under the illumination of single-cycle terahertz (THz) radiation, making THz-enhanced acoustics (TEA) a useful method for THz wave detection. During a single-cycle THz pulse with its peak field of 100 kV/cm, a pressure enhancement of 10% is observed throughout the acoustic spectrum up to 140 kHz, and the TEA signal is found to increase linearly with THz wave intensity. By using dual-color laser excitation to manipulate free electron drift, it is possible to modulate the enhanced acoustic signal and recover a coherent THz time-domain waveform by simply "listening" to the plasma. 相似文献
We comment on the recent Letter by S. P. Jamison et al. [Opt. Lett.31, 1753 (2006)] where the analysis of a chirped probe pulse that is electro-optically modulated by a terahertz pulse reportedly results in a new expression for the electric field. While in principle the derived expressions for the total field after the crystal are correct, in their treatment the authors implicitly assumed that the derived total field is identical to the measured field, without regard to the residual birefringence of a typical electro-optic crystal or a crossed analyzer. Based on this analysis neglecting birefringence, they report that earlier expressions of the temporal field are incorrect. Here we show, on the contrary, that for chirped single-shot terahertz measurement schemes that include residual birefringence, the temporally resolved electro-optic effect is described correctly by the commonly used expression in the literature. We verify this result with our experimental data. 相似文献
A total procedure for the terahertz wave brightness calibration using the quantum fluctuations at terahertz frequencies as a reference is formulated. An experimental proof for its theoretical background is provided. Klyshko method for the brightness calibration using spontaneous parametric down-conversion is modified, considering the case when the idler wave hits the terahertz frequency range and relative additives to the background signals induced by an external terahertz radiation can be measured both in Stokes and anti-Stokes ranges. It is shown at different temperatures that the thermal-fluctuation-induced signals have the same spectral and angular shapes, as the spontaneous parametric down-conversion signals, while the thermal-induced signal amplitudes are proportional to the number of photons in the thermal equilibrium modes. 相似文献