Numerical investigation of a scalable setup for efficient terahertz generation using a segmented tilted-pulse-front excitation

A hybrid-type terahertz pulse source is proposed for high energy terahertz pulse generation. It is the combination of the conventional tilted-pulse-front setup and a transmission stair-step echelon-faced nonlinear crystal with a period falling in the hundredmicrometer range. The most important advantage of the setup is the possibility of using plane parallel nonlinear optical crystal for producing good-quality, symmetric terahertz beam. Another advantage of the proposed setup is the significant reduction of imaging errors, which is important in the case of wide pump beams that are used in high energy experiments. A one dimensional model was developed for determining the terahertz generation efficiency, and it was used for quantitative comparison between the proposed new hybrid setup and previously introduced terahertz sources. With lithium niobate nonlinear material, calculations predict an approximately ten-fold increase in the efficiency of the presently described hybrid terahertz pulse source with respect to that of the earlier proposed setup, which utilizes a reflective stairstep echelon and a prism shaped nonlinear optical crystal. By using pump pulses of 50 mJ pulse energy, 500 fs pulse length and 8 mm beam spot radius, approximately 1% conversion efficiency and 0.5 mJ terahertz pulse energy can be reached with the newly proposed setup

Topological data analysis to identify cardiac resynchronization therapy patients exhibiting benefit from an implantable cardioverter-defibrillator

Background: Current guidelines recommend considering multiple factors while deciding between cardiac resynchronization therapy with a defbrillator (CRT-D) or a pacemaker (CRT-P). Nevertheless, it is still challenging to pinpoint those candidates who will beneft from choosing a CRT-D device in terms of survival. Objective: We aimed to use topological data analysis (TDA) to identify phenogroups of CRT patients in whom CRT-D is associated with better survival than CRT-P. Methods: We included 2603 patients who underwent CRT-D (54%) or CRT-P (46%) implantation at Semmelweis University between 2000 and 2018. The primary endpoint was all-cause mortality. We applied TDA to create a patient similarity network using 25 clinical features. Then, we identifed multiple phenogroups in the generated network and compared the groups’ clinical characteristics and survival. Results: Five- and 10-year mortality were 43 (40–46)% and 71 (67–74)% in patients with CRT-D and 48 (45–50)% and 71 (68–74)% in those with CRT-P, respectively. TDA created a circular network in which we could delineate fve phenogroups showing distinct patterns of clinical characteristics and outcomes. Three phenogroups (1, 2, and 3) included almost exclusively patients with non-ischemic etiology, whereas the other two phenogroups (4 and 5) predominantly comprised ischemic patients. Interestingly, only in phenogroups 2 and 5 were CRT-D associated with better survival than CRT-P (adjusted hazard ratio 0.61 [0.47–0.80], p<0.001 and adjusted hazard ratio 0.84 [0.71–0.99], p=0.033, respectively). Conclusions: By simultaneously evaluating various clinical features, TDA may identify patients with either ischemic or nonischemic etiology who will most likely beneft from the implantation of a CRT-D instead of a CRT-P

Optimization of the Tilted-Pulse-Front Terahertz Excitation Setup Containing Telescope

Optimization of the telescopic tilted-pulse-front terahertz excitation setup with respect to the imaging errors is given. A guideline is presented in the form of simple analytical formulae describing the optimal geometrical configuration of the telescopic setup. Pump pulse distortions and terahertz wave-front distortions are analyzed by ray tracing calculations supposing near-infrared pump pulses with 200 fs transform limited pulse length. The detrimental effects of imaging errors in a tilted-pulse-front terahertz source can be significantly reduced by using telescopic imaging instead of one-lens. It is also shown, that in the case of the one-lens setup significant, and in the case of the telescopic setup, less significant reduction of the imaging errors can be achieved by using achromat lens(es) instead of singlet one(s). Calculation results show that the telescopic setup consisting of two achromat lenses is the most promising choice among the practically relevant schemes

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

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

Possibility of high‑energy THz generation in LiTaO3

Due to the absence of the detrimental three-photon absorption, LiTaO3 is a promising crystal for terahertz generation when pumping with an 800-nm pump wavelength. The nonlinear optical, photorefractive and dielectric (except the bandwidth) properties at the optical and the terahertz wavelength are very similar to those of LiNbO3. The absorption coefficient and refractive index spectra of 1 mol% Mg-doped stoichiometric LiTaO3 measured by terahertz time domain spectroscopy are presented. Optimization calculations have been performed, and results for a hybrid-type high-energy terahertz source using LiTaO3 are presented. About 90 % diffraction efficiency is predicted with a practically feasible contact grating