Abstract:We demonstrate here an efficient THz source with low electrical power consumption. We have increased the maximum THz radiation power emitted from SI-GaAs based photoconductive emitters by two orders of magnitude. By irradiating the SI-GaAs substrate with Carbon-ions up to 2 m deep, we have created lot of defects and decreased the life time of photo-excited carriers inside the substrate. Depending on the irradiation dose we find 1 to 2 orders of magnitude decrease in total current flowing in the substrate, resulting in subsequent decrease of heat dissipation in the antenna. This has resulted in increasing maximum cut-off of the applied voltage across Photo-Conductive Emitter (PCE) electrodes to operate the device without thermal breakdown from ~35 V to > 150 V for the 25 m electrode gaps. At optimum operating conditions, carbon irradiated (10 14 ions/cm 2 ) PCEs give THz pulses with power about 100 times higher in comparison to the usual PCEs on SI-GaAs and electrical to THz power conversion efficiency has improved by a factor of ~ 800.Electromagnetic radiations having frequencies in Tera-hertz (THz) range (1THz = 10 12 Hz) are not so easy to generate [1] .But due to its applications in security imaging, bio-sensing, chemical identification, material characterization etc., there is high demand of high power THz sources, particularly sources which can generate short THz pulses with broadband spectrum. Till now, photoconductive emitters (PCEs) are known to be the best sources for high power THz pulse generation. Improving the efficiency of THz pulse sources with better designs or material, is one of the major goals of ongoing research in this field. There have been several attempts to increase the THz emission from these sources by modifying the electrical and optical properties of the semiconducting substrate [2] , design of electrodes [3] and patterning the active area of PCE in between the two electrodes [4] .In THz PCEs newly photo generated charge carriers (electron-hole pairs) via laser pulse of width less than 100 fs gets accelerated under already applied electric field and this sudden jump in number of free carriers and their acceleration gives sudden rise in the current. This sudden rise in current in pico-second time domain is responsible for THz pulse emission. In the case, where the semiconductor has carrier life time of less than a pico-second like LT-GaAs, current falls down to the dark level within picoseconds as electron hole pairs recombine with each other. Such materials are useful for the generation of bipolar THz pulses. In semiconductors like SI-GaAs which has carrier life time of more than 50 ps, fall in current takes relatively much longer time. Since electric field of the emitted THz pulse , where J(t)

We report the results of an investigation of low-frequency excess noise in high-current diamond diodes. It was found that the electronic excess noise of the diamond diodes is dominated by the 1/f and generation-recombination noise, which reveals itself as Lorentzian spectral features (f is the frequency). The generation-recombination bulges are characteristic of diamond diodes with lower turn-on voltages. The noise spectral density dependence on forward current, I, reveals three distinctive regions in all examined devices—it scales as I2 at the low (I < 10 μA) and high (I > 10 mA) currents and, rather unusually, remains nearly constant at the intermediate current range. The characteristic trap time constants, extracted from the noise data, show a uniquely strong dependence on current. Interestingly, the performance of the diamond diodes improves with the increasing temperature. The obtained results are important for the development of noise spectroscopy-based approaches for device reliability assessment for high-power diamond electronics.

Indium Sulphide (InS) single crystals are successfully grown by In flux. Single crystal X-ray diffraction shows orthorhombic structure of Pnnm space group. Ellipsometry measurements performed on the (010) oriented crystal exhibit low anisotropy in the 300-1000 nm wavelength range and consequently negligible THz emission is observed. Optical band gap of $2.09 eV$ is deduced from linear optical measurements. Nonlinear optical properties are studied by single beam Z-scan measurements at 800 nm, where two-photon absorption is present. Nonlinear refractive index and absorption coefficient are estimated to be $\eta_2$ = $2.3 10^{-11} cm^2/W$ and $\beta$= $62.4 cm/ GW$, respectively for excitation intensity of $0.32 GW/cm^2$. The origin of nonlinearity in InS crystal is accounted to be due to the third-order anharmonic motion of the bound electrons.Comment: 15 pages, 4 figures, 1 tabl

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-4]. These materials interact with the passing THz radiation, imprinting specific spectral features to it. Due to its long wavelength features, the spatial resolution of THz radiation is less compared to visible-IR waves, but the information gained from it is enormous. For a faithful detection of the THz pulses, it is necessary that the detectors (1) are not adding extra detector related features and (2) are sensitive at the same time. This requires that the detector material should not exhibit any absorption lines in the THz spectrum and the antenna design should be free of any sharp resonance features in the detection frequency range.