Channel-switchable single-/dual-wavelength single-longitudinal-mode laser and THz beat frequency generation up to 3.6 THz

We propose and demonstrate a simple approach to realize channel-switchable single-/dual-wavelength single-longitudinal-mode (SLM) lasers and switchable beat frequency generation in the THz frequency regime. It is a compact fiber-ring laser incorporating a Fabry–Pérot etalon, tunable filters, and a piece of unpumped polarization maintaining erbium-doped fiber (PM-EDF) as the saturable absorber. Two parallel-arranged tunable filters are configured inside the ring cavity to support switchable dual-wavelength SLM operation and consequent THz beat frequency generation. Switchable 19-channel 200-GHz ITU-grid-compatible single-wavelength SLM operation is implemented. Moreover, the channel-switchable dual-wavelength SLM laser and switchable THz beat frequency generation ranging from 0.2 to 3.6 THz with a tuning step of 0.2 THz are demonstrated in the experiment.     

Quasi-optical mixer for efficient sum and difference frequency sidebands generation at 1 THz mark

Construction details of recently developed mixer for generation of narrow band and continuously tunable submillimeter radiation are reviewed briefly. The measurements indicate the usability of such mixer design for the high resolution spectroscopical work at frequencies close to and above the 1 THz mark.The work described was performed by the author during his stay within Department of Atomic and Molecular Physics of Katholieke Universiteit, Nymegen, The Netherlands under the guidance of Prof.Dr. A. Dymanus.     

Novel concept for THz signals generation in heterostructures

We demonstrate by a Monte Carlo simulation that the reflection of quasi‐ballistically accelerated electrons at the interfaces of an In_0.52Al_0.48As/In_0.53Ga_0.47As/In_0.52Al_0.48As double‐heterojunction structure is able to generate current oscillations at frequencies in the THz range. The possibility of taking advantage of this mechanism to generate THz signals has been demonstrated in structures with well dimension close to the electron ballistic transport length in In_0.53Ga_0.47As.

     

Coherent bisection of 141 THz using sum frequency generation of 1064 and 709 nm radiation

The frequency interval (141 THz) that exists between 1064 nm radiation and the unusual semiconductor wavelength of 709 nm has been coherently divided by using an optical phase-locked loop to control a slave laser lying at the mean frequency of these two wavelengths. The 709 nm radiation has been generated by a combination of wavelength tuning in an extended cavity and temperature tuning of a ridge-waveguide semiconductor laser with a nominal wavelength of 728 nm. Two nonlinear processes have been used to produce the coherent division: the sum frequency mixing of 1064 and 709 nm radiation to produce 425 nm radiation and the second harmonic generation of 851 nm light to produce the same wavelength radiation.     

Integration across frequency bands for consonant identification

A comparison of the predictions of models of integration to data on the reception of consonants filtered into a variety of frequency bands is reported. New data on the consonant identification are presented. Three experiments were conducted testing the following bands: experiment I, 0-2100 Hz and 2100-4500 Hz; experiment II, 0-700 Hz combined with 700-1400, 1400-2100, 2100-2800, and 2800-4500 Hz; experiment III, all combinations of 700-1400, 1400-2100, 2100-2800, and 2800-4500 Hz. The predictions of four models, Fletcher's [Speech and Hearing in Communication (Van Nostrand, New York, 1950)] independent errors model, Massaro's fuzzy logical model of perception [Proc. Int. Congress of Phonetic Sciences, Stockholm, Vol. 3, pp. 106-113 (1987)], and Braida's pre-labelling and post-labelling models of integration [Q. J. Exp. Psychol. A 43, 647-677 (1991)], were compared in terms of their ability to predict combined-band scores. At least two models were capable of predicting performance for each combined-band condition. For experiment I, all models were able to make satisfactory predictions. For experiment II, a variant of the pre-labelling model was able to make satisfactory predictions. For experiment III, no model was able to make satisfactory predictions, but the fuzzy logical model of perception and a variant of the pre-labelling model made relatively good predictions. Thus the ability of the models to predict performance depended more on whether the condition included the lowest frequency band than on the adjacency or frequency separation.     

THz wave generation by repeated and continuous frequency conversions from pump wave to high-order Stokes waves

We propose a novel scheme for THz wave generation by repeated and continuous frequency conversions from pump wave to high-order Stokes waves (HSWs). The repeated frequency conversions are accomplished by oscillations of Stoke waves in resonant cavity (RC) where low-order Stokes waves (LSWs) are converted to high-order Stokes waves again and again. The continuous frequency conversions are accomplished by optimized cascaded difference frequency generation (OCDFG) where the poling periods of the optical crystal are aperiodic leading to the frequency conversions from low-order Stokes waves to high-order Stokes waves uninterruptedly and unidirectionally. Combined with the repeated and continuous frequency conversions, the optical-to-THz energy conversion efficiency (OTECE) exceeds 26% at 300 K and 43% at 100 K with pump intensities of 300 MW/cm².     

Pressure-broadening in the THz frequency region: The 1.113 THz line of water

It is well established that water plays a fundamental role in various atmospheric phenomena and that the accuracy of its collisional broadening parameters has a crucial influence on reduction of remote sensing data. Nevertheless, in this field the experimental data are still scarce and consequently the estimates reported in spectroscopic databases are not always reliable and/or accurate. In the view of filling this gap, the self-, N₂- and O₂-broadening parameters of the J=1_1,1←0_0,0 rotational transition of water (1.113 THz) have been determined at room temperature. The experimental investigation has also been supported by theoretical calculations.     

Simple frequency measurement chain to 30 THz

We report harmonic mixing experiments between a 72 GHz mm-wave and 3.7 THz NH₃-laser radiation, as well as between 3.7 THz and the 10 m R(30) CO₂-laser line. For the former mixing a semiconductor diode is used, while for the higher frequencies an MIM tunnel diode served as the nonlinear element. Beat signals are of sufficient signal to noise ratio for precise optical frequency measurement.Visiting from National Institute of Metrology, Beijing, P. R. China     

Application of high intensity THz pulses for gas high harmonic generation

The main effects of an intense THz pulse on gas high harmonic generation are studied via trajectory analysis on the single atom level. Spectral and temporal modifications to the generated radiation are highlighted.     

Intense broadband THz generation from femtosecond laser filamentation

Broadband and energetic terahertz (THz) pulses can be remotely generated in air through filamentation. We review such THz generation and detection in femtosecond Ti-sapphire laser induced remote filaments. New results are presented on the direct relationship between THz generation in a two color filament and induced N2 fluorescence through population trapping during molecular alignment and revival in air. This further supports the new technique of remote THz detection in air through the sensitive measurement of N2 fluorescence.     

太赫兹器件测试用高重复频率高压脉冲电源

为了开展太赫兹器件试验研究,设计了高重复频率脉冲电源系统。电源输出脉冲电压30 kV,脉冲电流200 mA,最大重复频率3 kHz,脉冲宽度10~100 μs,采用本地PLC加远程计算机控制模式来实现电源的本控及遥控。对系统的核心部件：充电电源和脉冲开关的拓扑结构进行了研究,并开展了仿真和试验。结果表明：采用LC串联谐振恒流充电技术以提高充电电源工作效率以及在负载打火情况下的可靠性;基于MOSFET并进行优化设计的串联脉冲开关可以获得快速的脉冲前后沿。电源系统的输出指标满足负载工作要求,在高重复频率、打火条件下能够稳定工作。     

THz generation by a suspended hybrid plasmonic waveguide

We present a suspended waveguide consists of a double hybrid plasmonic waveguide for the purpose of enhancing the conversion efficiency of terahertz (THz) wave generation using difference frequency generation process. We show that in the THz generation process, metal-air-metal waveguide facilitates the phase matching and reduces the propagation loss. Our numerical calculation shows that the conversion efficiency in these waveguide structures can be more than one order of magnitude larger than what has been achieved using regular metal-dielectric-metal waveguides.     

A novel double quantum well device for THz range frequency detection

A novel device has been proposed which uses a double quantum well structure for the detection of signals in the THz range. The technology for the manufacturing of such devices at this point of time is significantly mature so that such a device may be easily fabricated. The detector frequency may be varied from 10 to 90 THz by changing the well widths from 10 to 30 Å.     

Coherent control of THz wave generation in ambient air

Our study of THz wave generation in the pulsed laser induced air plasma with individually controlled phase, polarization, and amplitude of the optical fundamental wave (omega) and its second harmonic (2omega) indicates that the third-order nonlinear optical process mixing the omega and 2omega beams in the ionized plasma is the main mechanism of the efficient THz wave generation. The polarity and the strength of the emitted THz field are completely controlled by the relative phase between the omega and 2omega waves. The measured THz field amplitude is proportional to the pulse energy of the fundamental beam and to the square root of the pulse energy of the second-harmonic beam once the total optical pulse energy exceeds the plasma formation threshold. The optimal THz field is achieved when all waves (omega, 2omega, and THz waves) are at the same polarization in the four-wave-mixing process.     

THz radiation generation in axially magnetized collisional pair plasma

We investigate the electron-positron plasma for terahertz radiation generation by two Dark Hollow Gaussian beams (DHGBs), which result in multifocal radiations quite useful for various modern applications. In this process, the ponderomotive force acts as a driver for the generation of terahertz field and the realistic situation of collisional plasma under the application of axial magnetic field reveals an efficient radiation generation. An appreciable efficiency of more than 2% is achieved for the process.     

0.2 THz步进频率逆合成孔径雷达成像

研究设计了一种0.2 THz的步进频率雷达成像系统,带宽12 GHz,并利用逆合成孔径技术对物体进行二维高分辨成像。针对系统设计参数进行Matlab仿真,获得简单转台目标的二维逆合成孔径雷达图像。仿真结果表明,太赫兹雷达成像系统可实现目标的二维高分辨成像,横向和纵向距离可以达到cm级分辨率。     

0.2 THz步进频率逆合成孔径雷达成像

研究设计了一种0.2 THz的步进频率雷达成像系统,带宽12 GHz,并利用逆合成孔径技术对物体进行二维高分辨成像。针对系统设计参数进行Matlab仿真,获得简单转台目标的二维逆合成孔径雷达图像。仿真结果表明,太赫兹雷达成像系统可实现目标的二维高分辨成像,横向和纵向距离可以达到cm级分辨率。     

Terahertz optical frequency comb generation with optimized cascaded difference frequency generation

Optical Review - A novel scheme that generates terahertz optical frequency comb (THz OFC) based on optimized cascaded difference frequency generation (OCDFG) with an aperiodically poled lithium...