Abstract-Phase-matching in KTP crystal for THz wave generation at room temperature and 81 K

Chun-Rui, Qi-Kun Pan, Fei Chen, Grigory Lanskii, Nazar Nikolaev, Alexander Mamrashev, Yury Andreev, Arkadii Meshalkin



https://www.sciencedirect.com/science/article/pii/S1350449518306856

Optical properties of high-quality flux-grown potassium titanyl phosphate (KTiOPO4, KTP) crystals were studied at 81 K in the spectral range of 0.2-2.4 THz by terahertz time-domain spectroscopy and compared with the room temperature results. No strong phonon peaks were found at frequencies below 2.15 THz in the absorption spectra of αx ≈ αy components. At 81 K they do not exceed that of widely used GaSe crystal. Experimental data on the dispersion of refractive index at 81 K for THz waves polarized parallel to optical axes were approximated in the form of Sellmeier equations. Phase matching for collinear difference-frequency generation of visible and near-IR emission into the THz domain was found possible, as well as second harmonic generation within THz region that can be a basis for the new THz sources designs. Phase matching in KTP was found insensitive to temperature variation. These properties together with the exceptional set of other known physical properties render KTP crystal amongst the most prospective crystals for high-power THz wave generation under intense laser pumping.

Abstract- Modeling of an Uncooled CMOS THz Thermal Detector With Frequency-Selective Dipole Antenna and PTAT Temperature Sensor

Fei Chen,  Jiao Yang,  Zimeng Li

http://ieeexplore.ieee.org/document/8226858/

A thermal THz detector based on commercial CMOS technology working in room temperature is proposed. The THz electromagnetic wave is first selectively absorbed by an on-chip λ/4 dipole antenna realized in the metallization layer. The absorbed wave energy is then converted to Joule heat energy via a polysilicon resistor. The heat-generated temperature rise is finally detected by a proportional to absolute temperature sensor. The theoretical analysis and physical modeling of the detector including the mechanism of the electromagnetic energy absorption, the thermal conversion, and the electrical circuit response, are presented. The detectors at three typical THz frequencies of 1, 2.9, and 28.3 THz are designed in standard 0.18-μm CMOS technology and post-simulated to illustrate the detector's frequency-selective capability in the whole THz range. The simulated detector's voltage responsivity is 18.0 V/W at 1 THz, 18.9 V/W at 2.9 THz, and 18.6 V/W at 28.3 THz, respectively. The noise equivalent power is 1.7 μW/√Hz at the three frequencies.

Abstract-Doped GaSe crystals for laser frequency conversion

Jin Guo^1,2, Ji-Jiang Xie^1,2, Dian-Jun Li^1,2, Gui-Long Yang^1,2, Fei Chen^1,2, Chun-Rui Wang^1,2, Lai-Ming Zhang¹, Yury M Andreev^3,4, Konstantin A Kokh^5,6, Gregory V Lanskii^3,4 and Valery A Svetlichnyi⁴

1. ¹State Key Laboratory of Laser Interaction with Matter, Changchun Institute of Optics, Fine Mechanics and Physics, CAS, Changchun 130033, China
2. ²Innovation Laboratory of Electro-Optical Countermeasures Technology, Changchun Institute of Optics, Fine Mechanics and Physics, CAS, Changchun 130033, China
3. ³Laboratory of Geosphere-Biosphere Interactions, Institute of Monitoring of Climatic and Ecological Systems, SB RAS, Tomsk 634055, Russia
4. ⁴Laboratory of Advanced Materials and Technologies, Siberian Physical-Technical Institute of Tomsk State University, Tomsk 634050, Russia
5. ⁵Crystal Growth Laboratory, Institute of Geology and Mineralogy, SB RAS, Novosibirsk 630090, Russia
6. ⁶Novosibirsk State University, Novosibirsk 630090, Russia

Correspondence: VA Svetlichnyi, Email: v_svetlichnyi@bk.ru

Received 24 December 2014; Revised 20 August 2015; Accepted 20 August 2015

http://www.nature.com/lsa/journal/v4/n12/full/lsa2015135a.html

In this review, we introduce the current state of the art of the growth technology of pure, lightly doped, and heavily doped (solid solution) nonlinear gallium selenide (GaSe) crystals that are able to generate broadband emission from the near infrared (IR) (0.8 μm) through the mid- and far-IR (terahertz (THz)) ranges and further into the millimeter wave (5.64 mm) range. For the first time, we show that appropriate doping is an efficient method controlling a range of the physical properties of GaSe crystals that are responsible for frequency conversion efficiency and exploitation parameters. After appropriate doping, uniform crystals grown by a modified technology with heat field rotation possess up to 3 times lower absorption coefficient in the main transparency window and THz range. Moreover, doping provides the following benefits: raises by up to 5 times the optical damage threshold; almost eliminates two-photon absorption; allows for dispersion control in the THz range independent of the mid-IR dispersion; and enables crystal processing in arbitrary directions due to the strengthened lattice. Finally, doped GaSe demonstrated better usefulness for processing compared with GaSe grown by the conventional technology and up to 15 times higher frequency conversion efficiency.