There is a general lack of compact electromagnetic radiation sources between 1 and 10 terahertz (THz). This a challenging spectral region lying between optical devices at high frequencies and electronic devices at low frequencies. While technologically very underdeveloped the THz region has the promise to be of significant technological importance, yet demonstrating its relevance has proven difficult due to the immaturity of the area. While the last decade has seen much experimental work in ultra-short pulsed terahertz sources, many applications will require continuous wave (cw) sources, which are just beginning to demonstrate adequate performance for application use. In this project, we proposed examination of two potential THz sources based on intersubband semiconductor transitions, which were as yet unproven. In particular we wished to explore quantum cascade lasers based sources and electronic based harmonic generators. Shortly after the beginning of the project, we shifted our emphasis to the quantum cascade lasers due to two events; the publication of the first THz quantum cascade laser by another group thereby proving feasibility, and the temporary shut down of the UC Santa Barbara free-electron lasers which were to be used as the pump source for the harmonic generation. The development efforts focused on two separate cascade laser thrusts. The ultimate goal of the first thrust was for a quantum cascade laser to simultaneously emit two mid-infrared frequencies differin

Terahertz (THz) spectral band, from about 0.1 to 15 THz, is one of the least explored yet most technologically transformative spectral regions. A large number of interesting scientific phenomena are only accessible by THz photons and THz radiation also finds a lot of practical applications. However, for a long time, THz scientific research and technological development is greatly limited due to the technical difficulties in making efficient and compact THz emitters and detectors, and controlling THz waves has been proven to be more difficult. On the other hand, artificially subwavelength structured materials called metamaterials, have been actively pursued and developed, which enables people to tailor their optical responses or nonlinearities in THz region, setting them among the most promising candidates for the next generation optoelectronic devices to generate and manipulate THz waves. Here we present our design and study of (1) a novel split ring resonator (SRR) based high efficiency THz emitter and (2) all-optical photo-imprinted reconfigurable THz diffraction gratings. Firstly, the THz emitter is composed of a single layer of 40nm thick gold film with SRR lattice constant 382nm on a 1mm thick suprasil substrate. THz waves are generated by pumping the SRR magnetic dipole resonance at 1500 nm. The demonstrated second-order sheet nonlinear susceptibility is three orders of magnitude higher than those of conventional crystals and thin films. The emitter can be tailored to p

alternative to X-rays for producing high resolution images of the interior of solid objects. Terahertz radiation occupies a middle ground where the ranges Terahertz radiation – also known as terahertz waves, tremendously high frequency (THF), T-rays, T-waves, T-light, or T-lux– consists of electromagnetic waves within the frequency band from 0.1 to 10 terahertz (symbol THz), as designated by the International Telecommunication Union (ITU). One terahertz is 1012 Hz or 1,000 GHz. Wavelengths of terahertz radiation range from 3 millimeters and 30 micr Terahertz radiation – also known as terahertz waves, tremendously high frequency (THF), T-rays, T-waves, T-light, or T-lux– consists of electromagnetic waves within the frequency band from 0.1 to 10 terahertz (symbol THz), as designated by the International Telecommunication Union (ITU). One terahertz is 1012 Hz or 1,000 GHz. Wavelengths of terahertz radiation range from 3 millimeters and 30 micrometers (3 mm = 3000 μm to 30 μm), sometimes known as the submillimeter band, and its radiation as submillimeter waves, especially in astronomy. This band of electromagnetic radiation lies within the transition region between microwave and far infrared and can be regarded as either. Compared to lower radio frequencies, terahertz radiation is strongly absorbed by the gases of the atmosphere, and in air, most of the energy is attenuated within a few meters, so it is not practical for long distance terrestrial radio communication. It can penetrate thin layers of materials but is blocked by thicker objects. THz beams transmitted through materials can be used for material characterization, layer inspection, relief measurement, and as a lower-energy alternative to X-rays for producing high resolution images of the interior of solid objects. Terahertz radiation occupies a middle ground where the ranges of microwaves and infrared light waves overlap, known as the "terahertz gap"; it is called a "gap" because the technology for its generation and manipulation is still in its infancy. The generation and modulation of electromagnetic waves in this frequency range ceases to be possible by the conventional electronic devices used to generate radio waves and microwaves, requiring the development of new devices and techniques. As of 2012,…

in measuring the temperature dependence of blackbody radiation of ‘great wave lengths’, including at wavelengths in what we would now call the terahertz frequency region, was instrumental in providing Max Planck with the crucial data in 1900 to confirm his hypothesis of what became known as Planck’s radiation law, which heralded the dawn of quantum mechanics [ 4 ]. Owing to the difficulties in fabricating compact solid-state sources and detectors of terahertz radiation, researchers focused attention on all-optical techniques, employing near-IR femtosecond pulsed lasers to generate pulses of terahertz radiation through electro-optic rectification in nonlinear crystals or from a device known as a photoconductive switch [ 5 ]. The latter comprises a chip of biased semiconductor where the absorption of the femtosecond pulse allows a transient current to flow. A popular material for this is GaAs, which can be carefully engineered and grown below the usual growth temperature to provide the rather counter-intuitive properties of having simultaneously short electron and hole recombination lifetimes, high electron and hole mobilities and a high resistivity [ 6 ]. This material, known as low-temperature-grown (LT-) GaAs, was developed in the mid-1980s [ 7 ], and the subsequent development of coherent broadband terahertz spectroscopy and imaging systems led to the surge of international activity in this field and arguably started the modern era of terahertz science and technology. Developments in terahertz technology have also been driven by the wide range of materials that can be explored in the terahertz range, including organic and inorganic crystalline materials and gases, which exhibit sharp characteristic (ro-)vibrational features in the THz frequency range, see [ 8 ], for example. The terahertz spectra are also sensitive to both intra- and inter-vibrational molecular modes, making terahertz spectroscopy highly sensitive to small changes in crystalline structure. In man