We conduct time domain spectroscopy studies and shows that graphene sheet amplifies an incoming terahertz field. The graphene emission spectra dependency on laser pumping intensity shows a threshold like behavior, testifying the occurrence of the negative conductivity and the population inversion in the terahertz range, paving the way for a new class room temperature graphene based terahertz lasers.
Experimental THz experiments on hen egg-white lysozyme (HEWL) with and without the ligand NAG3 has revealed that the protein's solvent structure on the picosecond time scale is in integral part of the regulation mechanism of the enzyme. Our investigation into the low frequency dynamics of the protein has uncovered that the counterions in the solvent shell mediate the collective dynamics of both the...
We report the THz field-induced-second-harmonic generation in various biomolecules including amino acids, proteins and sugars. The THz field induced optical second harmonic (SH) signal depends on the strength of THz beam and on the relative polarizations of optical and THz beam. The THz waveform is coherently retrieved from the time dependent SH signal.
A 95 GHz gyrotron capable of generating CW power levels in excess of 2 MW is currently under development at CPI. Recently, peak output powers in excess of 1.9 MW were demonstrated with measured efficiencies of 40%. Detailed test results and future plans will be presented.
We examined a new type of organic nonlinear optical crystal, 4-dimethylamino-N-methyl-4-stilbazolium p-chlorobenzenesulfonate (DASC) as terahertz (THz) wave source via difference frequency generation (DFG), by comparing the THz-wave radiation from DAST crystal. We demonstrated the possibility that DASC crystal has some advantages as THz-DFG source in efficiency and damage threshold.
We investigated the Cherenkov phase-matched tunable THz-wave radiation via difference frequency generation from a lithium niobate crystal (LN) excited by a dual wavelength Cr:Forsterite laser by using the two types of detectors, Si bolometer and Shottkey barrier diode (SBD). We demonstrated that Si bolometer can be useful in the frequency range of 0.2 to 2.3THz and SBD can be useful in the frequency...
Vector Network Analyzers are among the most important test and measurement systems in modern microwave laboratories. If the terahertz frequency band is to be developed to the full potential, it is critical that VNAs and other systems such as signal generators and analyzers be extended to higher frequency. This paper will describe the development of VNA frequency extenders for use up to 1,100GHz.
High power Terahertz vacuum source are critical need in various applications such as medical, security, communication, etc. The power and life of these types of devices mainly depends on cathode. Due to miniature structure of the THz devices, it is very much difficult to obtain high power using conventional low current density dispenser cathode. As a result development of high current density dispenser...
We report the analytical calculations and finite domain time domain simulations of a travelling wave photomixer based on double plasmon waveguide driven at 1.55 μm wavelength. The obtained results were used to set the geometrical parameters of fabricated devices.
We present the line dipole image method which is based on an analytic image theory. The probe tip on the sample substrate is approximated by a metallic sphere for calculation. Within the quasi-electrostatic limit, the exact image theory was iteratively applied to obtain the total induced dipole moment for the sample-substrate system. The experimental approach curves are explained. The measurements...
The widespread adoption of THz based applications has been hindered by the lack of a real-time, broad-band, cost-effective THz camera with sufficient sensitivity to enable applications in markets as diverse as security, non-destructive evaluation, and biomedical imaging. This technological gap can be filled through the development of an 80 × 64 pixel array of Sb-heterostructure backward diodes (Sb-HBDs)...
Graphene has emerged as the semiconductor with the highest reported mobility of carriers at room temperature making it suitable for terahertz applications. The plasmon frequencies of graphene are also in the terahertz range. Plasmons in graphene interact strongly with electrons and holes and plasmon emission and absorption are the fastest mechanisms for electon-hole recombination and generation. Plasmon...
Ultrafast gain switching of THz quantum cascade lasers is demonstrated and applied to amplify sub-ps THz pulses as well as to initiate THz laser emission with a controlled phase. Impact on THz time domain spectroscopy and on future development for mode-locking will be discussed.
An electrically tunable phase shifter based on liquid crystals (LC) is presented first time, using a specific electrode structure which provides the advantage to enable fully electrical tuning between the two states of the phase shifter. That reduces the mechanical complexity of the instant device compared to that of devices using magnetostatic orientation of the LC .
Compressive measurement enables image formation from sparse and irregular arrays. In MMW and terahertz imaging, compressive measurement may lead to a preference for fewer but more complex transceivers over dense arrays of simple transceivers (e.g. conventional focal planes.)
The main properties of planar Goubau waveguides in the THz range are reported. Attenuation, dispersion and electric field confinement are measured using a guided-wave spectroscopy system based on a freely positionable electro-optic detector, and simulated using 3D electromagnetic field solver.
A terahertz absorption spectrometer for high-resolution molecular spectroscopy is realized. The spectrometer is based on a multimode quantum-cascade laser. The design and performance of the spectrometer are presented. Three aspects are discussed: sensitivity, frequency calibration, and frequency multiplexing.
A high-Q quasi-optical resonator operating at 400 GHz and 650 GHz is used to measure the conductivity of metal samples with nano-scale textures made using a LIGA-like nanoimprinting process. The results explore the effect of surface roughness on effective conductivity in the terahertz regime.
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