By adding different inductance to the bias voltage circuit of the photoconductive antenna, the changes of the time-domain waveform peak value and spectral bandwidth of THz radiation from the photoconductive antenna were observed, and further studied the influence on the characteristics of THz radiation from the inductance of photoconductive antenna circuit when designing the photoconductive antenna. According to the experiments, it is found that different inductance values have no prominent effect on the peak value of time-domain waveform and spectrum bandwidth of THz radiation from the photoconductive antenna.
The ultrafast photoconductive characteristics of GaAs were investigated by the optical-pump terahertz-probe (OPTP) method at room temperature. In our experiment, a significant decrease of the terahertz transmittance has been observed when the time delay between the optical pump pulse and the terahertz probe pulse was adjusted. When the optical excitation occurred on the surface of GaAs, the free carriers increase. Results regressed the experimental curve and obtained the carrier lifetime is 681ps.
In this paper, cross-linked polyethylene (XLPE) was analyzed by THz time domain spectroscopy (TDS) system at room temperature. By recording time domain signal of terahertz radiation field, frequency spectrum can be obtained by Fourier transform. Then the refractive index and dielectric constant in THz band are calculated. This proves that the THz-TDS system has a potential application for detecting the aging characteristic of XLPE.
The photoconductive antenna (PCA) is one of the most common devices to generate terahertz (THz) wave, whose radiation efficiency is largely determined by the working conditions. In order to improve the power of THz wave, the influence of pump laser and bias voltage on the intensity of the THz wave radiated by PCA was studied through experiment and the optimum working conditions of PCA was obtained through the theoretical analysis, these are the maximum safe voltage and saturated laser energy. Only under the optimum conditions can the signal-to-noise ratio(SNR)of THz wave radiated by PCA be the highest and the PCA would not breakdown.
To analyze the carrier lifetime of Si, a 0.4 mm thickness high-resistivity silicon had been investigated by the optical-pump-terahertz-probe (OPTP) system. The terahertz time domain curve and frequency spectrum (bandwidth of > 6THz) of Si are achieved by the time domain spectroscopy mode, and its characteristic parameters, including refractive index and absorption coefficient, were obtained. And the carrier lifetime of Si was measured by the OPTP mode, the result is about 905 ps.
The challenges of terahertz (THz) technology exist in the development of new or improved sources of THz
radiation and detection technologies. In general, inexpensive, fast, and room temperature operation THz detectors are not
readily available. A glow discharge neon lamp can serve as a THz detector, and holds great potential for various THz
sensing and imaging applications. Neon lamps THz detector has many advantages such as low cost, fast response time,
large dynamic range, broad spectral range, and room temperature operation. In this paper, the performance of the THz
detector based on glow discharge neon lamps was evaluated. The detector was successfully used in a THz imaging
system, the THz images obtained by the detector was demonstrated and compared with that obtained by a Schottky
detector.at
The structure and working mechanism of a photoconductive photodetector are compared with a p+-i-n+ (PIN) photodiode
and a metal-semiconductor-metal (MSM) photodetector which is regarded as two back-to-back Schottky barrier
photodiodes. Because a photoconductive photodetector has the features of high critical field strength, especially no
junction capacitance and no dead zone, it has the main merits of high signal-noise ratio, ultrafast response and high
quantum efficiency. We fabricate two photoconductive photodetectors in a lateral configuration on a semi-insulating (SI)
gallium arsenide (GaAs) wafer, which wavelength range of response is from UV to 1.73μm due to two-photon
absorption. It is shown by the volt-ampere characteristics curve that the dark leakage current of 30μm-gap SI GaAs
photoconductive photodetector at a bias field of 66 V/cm is less than 1.2 μA. Our experiment has demonstrated that SI
GaAs photoconductive photodetectors are noteworthily superior to high-speed Si PIN photodetectors to measure
ultrashort pulse lasers with the properties of ultrafast response, ultrawide spectral range, high signal-noise ratio and ease
of fabrication.
In this paper, experiments of a lateral semi-insulating GaAs photoconductive semiconductor switch triggered by nanosecond laser pulses were reported. The switches were insulated by solid multi-layer transparent dielectrics. Jitter-free electrical pulses with steady voltage amplitude from the 0.5 mm-gap GaAs switches were observed when biased with low voltage and triggered by serial laser pulses. Its change of amplitude was less than 1.2%, the triggered jitter-time was less than 10ps, and pulse width was up to sub-nanosecond. The effect of pulse energy change on the amplitude generated photoconductive semiconductor switch was analyzed. It was indicated that ultra-fast electrical pulse with steady voltage amplitude and pico-second triggered jitter-time can be obtained by controlling switch trigger condition and optimizing switch design.
GaAs PCSS's can work under linear and nonlinear modes. When the PCSS's work at the field below 3.5 kV/cm, current pulse string and corresponding light pulse string have the same rise time and pulse width. The resistance of PCSS's recovers, as soon as the light pulse disappears. When the electrical field is larger than 4.3 kV/cm, the light energy is greater than 0.46 mJ, GaAs-PCSS's work at nonlinear mode, which also is called high gain mode or lock-on effect. By calculation, Gunn domains come into being in GaAs in lock-on effect, and the high-gain mechanism is explained by optically activated charge domain model. So the microcosmic conditions of lock-on have been found. The requirement on the triggering laser energy is essential to meet the requirement of Gunn-domain formation by generating enough carriers. The requirement on the electrical field threshold is borne on the requirement of NDR threshold (Gunn threshold), which ranges from 3.2 kV/cm to 4 kV/cm for GaAs. In our experiments, the electric field threshold of high-gain mode is from 4.1 kV/cm to 11 kV/cm, which is higher than NDR threshold of GaAs. We can reduce the electrical field down to Gunn threshold by designing the external circuit. In this paper, two circuits are introduced which is designed by Sandia National Laboratories, and can be used to induce fast recovery from lock-on.
We report the experimental results of a large-aperture biased semi-insulating GaAs photoconductive dipole antenna, with a gap of 3 mm between two Au/Ge/Ni electrodes, triggered by 800 nm Ti-sapphire laser pulses with 82 MHz repetition rate. A direct comparison is made between insulated GaAs dipole antenna with a Si3N4 layer and bare GaAs dipole antenna. The radiation amplitude present linear to the exciting power when the applied voltage is fixed. The Si3N4 insulated GaAs dipole antenna can hold higher biased voltage than normal GaAs dipole antenna; its terahertz radiation generation efficiency is significantly higher than normal GaAs dipole antenna. The maximum voltage can be hold by the Si3N4 insulated GaAs dipole antenna is about 2 times higher than normal GaAs dipole antennas. We simulate the THz radiations from insulated GaAs dipole antenna with Si3N4 layer and bare GaAs dipole antenna. The waveforms of the simulated normalized surface field are in close agreement with the waveforms of the experimental results.
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