Using a 400 μJ ytterbium laser combined with a novel pulse compression technique, we demonstrate a state-of-the-art terahertz (THz) source from the tilted-pulse front pumping scheme in lithium niobate at room temperature with record efficiency of 1.3% capable of generating 74 mW of average power and 400 kV/cm at focus. Key points of this demonstration include the use of a pump pulse duration of 280 fs in combination with a stair-step echelon mirror and an off-axis ellipsoidal mirror. This source has unmatched characteristics of generating intense and powerful THz pulses at the same time and remains highly scalable as compared to existing Ti:sapphire-based THz sources pumped in the millijoule range.
Cost effective imaging is required for a wide range of scientific and engineering applications. For electromagnetic waves in the terahertz (THz) frequency range, a key missing element that has prevented widespread applications in this spectral range is an inexpensive and efficient imaging device. In recent years, vanadium oxide based thermal sensors have rapidly entered the market for night vision capability. At the same time, sensors based on this technology have been applied to the THz domain, but with two orders of magnitude larger pricing range. Here we show that, with a simple modification, a commercially available thermal imaging camera can function as a THz imaging device. By comparing a commercially available THz camera and this low-cost device, we identify the main sensitivity difference is not attributed to anything intrinsic to the devices, but rather to the analog-to-digital converter and dynamic background subtraction capability. This demonstration of a low-cost THz camera may aid in the rapid development of affordable THz imaging solutions for industrial and scientific applications.
Ultra-violet (UV) light emitting diodes (LEDs) using III-N quantum dot (QD) active regions have been fabricated by molecular beam epitaxy on (0001)-oriented sapphire substrates. By using the epitaxial compressive stress between the QD material and the template/barrier layers, leading to a 2D-3D growth mode transition, self-assembled Al y Ga 1-y N QDs with a nominal Al composition of 10% and 20% have been fabricated on Al 0.6 Ga 0.4 N. Atomic force microscopy and transmission electron microscopy measurements show high QD densities, ranging between 2x10 11 -5x10 11 cm -2 , and height and diameter distributions between 1.5 -3 nm and 5 -20 nm. LED structures including two different Al y Ga 1-y N / Al 0.6 Ga 0.4 N (0001) QD active injection current density has also been investigated and is discussed in terms of injection and recombination mechanisms in the devices.
In this work, we study THz generation and detection using cadmium telluride (CdTe) crystals pumped by amplified (1.025 μm wavelength) and oscillator (1.045 μm wavelength) ytterbium (Yb) lasers. For each laser, we compare the performances of the CdTe THz emitter and detector to those of GaP crystals. Under optimum conditions, we demonstrate that the former shows 3 and 5 times better performances compared with the latter for detection and generation, respectively. When pumped by an amplified Yb laser, we find that the CdTe crystal is more efficient than the GaP crystal for emission at optical fluences lower than 250 μJ/cm2. Although CdTe has some limitations in comparison with GaP, such as high THz absorption above 1 THz and the appearance of two-photon absorption at relatively low optical intensity, our findings demonstrate the potential of this crystal to be used as the emitter and detector in combination with the Yb laser.
The electro-optical sampling method is a widely used technique for the detection of terahertz (THz) waves. During the last thirty years, various electro-optical sensors have been proposed, but mainly working with a near-infrared probe. Here we demonstrate efficient detection of terahertz radiation up to 2.5 THz using a (110)-cut zinc sulfide (ZnS) crystals with the second harmonic of an amplified solid-state ytterbium laser beam at 512 nm. To validate its characteristics, we compare its performance with that of the cadmium telluride (CdTe) crystal probed at the fundamental wavelength of the laser.
In this work, we experimentally demonstrate the generation of 30 nm of spectral broadening in a bulk cadmium sulfide (CdS) semiconductor generated by a 280 fs long pulse at 1.024 µm wavelength and with a microjoule energy level. Using second-harmonic generation in barium borate, the complex ring pattern induced by self-focusing due to the strong nonlinear interaction of the laser pulse in the pair of CdS crystals is filtered out using second-harmonic nonlinear crystal to recover a Gaussian shape spatial profile. We also present the temporal compression of the resulting 512 nm laser pulse up to 45 fs by using a pair of standard transmissive gratings, leading to a pulse compression factor of 6.13. This technique is compact, inexpensive, and robust and produces ultrafast optical pulses from an input laser pulse whose duration and energy range are generally incompatible with a straightforward compression method in nonlinear optical fibers.
Packet-modulated communication may play a pivotal role in the future of short-range communications at terahertz (THz) frequencies. As with ultra-wideband communication, the advantageous of this type of communication are its extremely short duration, immunity to multipath fading, wide bandwidth and low power spectral density. However, due to the lack of a fast modulation method, packet-modulated pulse communication at THz frequencies has not yet been demonstrated. Here we present a method for the generation and modulation of a coded THz pulse train. Our scheme is based on the combination of a spintronic THz emitter (STE) with an echelon mirror and a digital micromirror device. This highly scalable configuration is capable of modulating hundred or more THz pulses in parallel with sub-picosecond accuracy and is versatile for various modulation protocols. Strikingly, the temporal resolution of our modulation scheme depends on geometric optics and not on a high-speed electronic device. Furthermore, the ability of STEs to generate quasi-continuous THz pulses offers an alternative solution to the photomixer, a key THz communication technology, and thus could lead to a promising new THz communication modality.
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