Abstract-High power terahertz (THz) radiation generation through the nonlinear interaction of cosh-Gaussian laser beams in cluster plasma

Conference Proceedings

Prateek Varshney,  Vikrant Saxena, Vivek Sajal

https://aip.scitation.org/doi/10.1063/1.5120954

The nonlinear interaction of two co-propagating cosh-Gaussian laser beams in a cluster plasma is investigated and the electric field amplitude of emitted terahertz is evaluated. Due to spatial non-uniformity in the intensity of laser beam profiles, the cluster electron experience a nonlinear ponderomotive force at beat wave frequency in the perpendicular direction of the propagation wave. Due to this ponderomotive force, the cluster electrons acquire nonlinear oscillatory velocity. This oscillatory velocity couples with preformed density ripples to generate a strong transient nonlinear current which resonantly derives terahertz wave in the propagation direction of laser beams. The effects of laser beams and plasma parameters, including the decentered parameter, laser beam width, plasma density and amplitude of density ripples on the evaluation of THz electric field are examined, and it is found that the shape of generated THz radiation can be tuned by laser parameters. The THz filed amplitude strongly depends on the index of the decentered parameters of cosh-Gaussian beams and amplitude of density ripples.

Abstract-High power surface emitting terahertz laser with hybrid second- and fourth-order Bragg gratings

Yuan Jin, Liang Gao, Ji Chen, Chongzhao Wu, John L. Reno, Sushil Kumar,


https://www.nature.com/articles/s41467-018-03697-9


A surface-emitting distributed feedback (DFB) laser with second-order gratings typically excites an antisymmetric mode that has low radiative efficiency and a double-lobed far-field beam. The radiative efficiency could be increased by using curved and chirped gratings for infrared diode lasers, plasmon-assisted mode selection for mid-infrared quantum cascade lasers (QCLs), and graded photonic structures for terahertz QCLs. Here, we demonstrate a new hybrid grating scheme that uses a superposition of second and fourth-order Bragg gratings that excite a symmetric mode with much greater radiative efficiency. The scheme is implemented for terahertz QCLs with metallic waveguides. Peak power output of 170 mW with a slope-efficiency of 993 mW A−1 is detected with robust single-mode single-lobed emission for a 3.4 THz QCL operating at 62 K. The hybrid grating scheme is arguably simpler to implement than aforementioned DFB schemes and could be used to increase power output for surface-emitting DFB lasers at any wavelength.

SBIR-STTR-Far-Tech-DOE Robust S-Band thermionic RF gun with improved back-bombardment suppression

FAR-TECH, Inc.

10350 Science Center Drive, Ste 150, San Diego, CA, 92121-1136

Name: David Newsham
Title: Dr.
Phone: (858) 455-6655
Email: newsham@far-tech.com

https://www.sbir.gov/sbirsearch/detail/1209409

Thermionic electron sources operating a microwave frequencies with longer lifetimes and increased performance will improve the reliability of synchrotron light sources and a new generation of high power terahertz light sources. Increasing the reliability of the electrons sources will improve the stability of operation for users. The robust thermionic electron source uses a short initial cell, followed by a cavity that is electrically uncoupled from the initial cell. The initial short gap delays the launch phase at which back-bombardment of the electrons onto the cathode will occur. This effectively decreases the beam power that will heat the cathode and increased the possible pulse width. The second cavity is uncoupled to the first cavity and is driven independently to maximize beam capture. In Phase I, the feasibility of producing the novel gun design will be determined through RF and beam dynamics simulation. The effectiveness of the short first cell followed by an independently driven cavity will be verified. The ability to cancel the coupling between the two cells will be confirmed and a design of the whole cavity structure will be developed. The cathode mounting system will be designed. Thermionic electron sources operating at microwave frequencies are current limited by electrons that reflect back from the radio frequency fields and heat the cathode. A novel cavity design is being investigated that will decrease the number of reflected electrons and improve the efficiency of the overall electron source. Commercial Applications and Other Benefits: This cavity will be an improvement over existing thermionic guns, allowing for operation at increased duty factor do to the reduction of the electron back-bombardment on the cathode. It has potential uses in synchrotron light sources and high power terahertz sources.

Abstract-Hybrid tilted-pulse-front excitation scheme for efficient generation of high-energy terahertz pulses

L. Pálfalvi, Z. Ollmann, L. Tokodi, and J. Hebling
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-8-8156

Conception of a hybrid type tilted-pulse-front pumping scheme for the generation of high-energy terahertz pulses is presented. The proposed setup is the combination of the conventional setup containing imaging optics and the contact grating. The solution was developed for nonlinear materials requiring large pulse-front-tilt angle, like LiNbO3. Due to the creation of the pulse-front-tilt in two steps the limitations of imaging errors can be significantly reduced. Furthermore the necessary grating constant of the contact grating can be larger compared to the simple contact grating scheme making possible the fabrication of the grating profile with significantly higher precision. A detailed optimization procedure with respect to the diffraction efficiency on the contact grating is given for LiNbO3. Instructions are also given how to construct the geometry of the setup in order to minimize imaging errors. Examples are given for LiNbO3 based practically realizable, optimized schemes with reduced imaging errors and high diffraction efficiency on the contact grating.

© 2016 Optical Society of America

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Abstract-High harmonic terahertz confocal gyrotron with nonuniform electron beam

Wenjie Fu¹, Xiaotong Guan¹ and Yang Yan¹
http://scitation.aip.org/content/aip/journal/pop/23/1/10.1063/1.4939213
1 THz Research Center, School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054, China
Phys. Plasmas 23, 013301 (2016); http://dx.doi.org/10.1063/1.4939213

The harmonic confocal gyrotron with nonuniform electron beam is proposed in this paper in order to develop compact and high power terahertz radiation source. A 0.56 THz third harmonicconfocal gyrotron with a dual arc section nonuniform electron beam has been designed and investigated. The studies show that confocal cavity has extremely low mode density, and has great advantage to operate at high harmonic. Nonuniform electron beam is an approach to improve output power and interaction efficiency of confocal gyrotron. A dual arc beam magnetron injection gun for designed confocal gyrotron has been developed and presented in this paper.