Possibility of CO2 laser-pumped multi-millijoule-level ultrafast pulse terahertz sources.

In the last decade, intense research has been witnessed on developing compact, terahertz (THz) driven electron accelerators, producing electrons with a sub-MeV-few tens of MeV energy. Such economical devices could be used in scientific and material research and medical treatments. However, until now, the extremely high-energy THz pulses needed by the THz counterparts of the microwave accelerators were generated by optical rectification (OR) of ultrafast Ti:sapphire or Yb laser pulses. These lasers, however, are not very effective. Because of this, we use numerical simulations to investigate the possibility of generating high-energy THz pulses by the OR of pulses produced by CO2 lasers, which can have high plug-in efficiency. The results obtained supposing optical rectification (OR) in GaAs demonstrate that consideration of the self-phase-modulation (SPM) and the second-harmonic-generation (SHG) processes is indispensable in the design of CO2 laser-based THz sources. More interestingly, although these two processes hinder achieving high laser-to-THz conversion efficiency, they can still surpass the 1.5% value, ensuring high system efficiency and making the CO2 laser OR system a promising THz source. Our finding also has important implications for other middle-infrared laser-pumped OR-based THz sources.

Demonstration of an imaging-free terahertz generation setup using segmented tilted-pulse-front excitation.

A novel, to the best of our knowledge, compact, imaging-free, tilted-pulse-front (TPF) pumped terahertz (THz) source based on a LiNbO3 slab with a small wedge angle (< 8°) and with an echelon microstructure on its input surface has been demonstrated. Single-cycle pulses of more than 40-µJ energy and 0.28-THz central frequency have been generated by 100-mJ, 400-fs pump pulses with 4.1 × 10-4 efficiency and excellent focusability. The peak electric field value focused by a single parabolic mirror was 540 kV/cm. Using 200-fs-long pump pulses, the efficiency increased to 1.0 × 10-3, which is in qualitative agreement with the measured increased diffraction efficiency in the velocity matched diffraction order. A further ∼8x increase in efficiency is expected by pumping a cryogenically cooled wedged echelon with appropriate step sizes, better microstructured surface quality, and antireflection coating on both the input and the output sides. THz generation efficiency maxima were found at ∼2.7-mm crystal thickness for both pump pulse durations. The focused THz beam was diffraction limited within 5% accuracy. Compared to conventional THz sources, this setup is very compact, easy to align, can be pumped by larger beam sizes maintaining the high THz generation efficiency, and produces THz pulses with superior focusability.

Scalable microstructured semiconductor THz pulse sources.

In recent years several microstructured lithium niobate THz pulse source were suggested for high-energy applications. Two types of those, the reflective and the transmissive nonlinear slab are adopted here for semiconductors. These new sources are scalable both in THz energy and size. Furthermore, they can outperform the already demonstrated contact grating source in diffraction and THz generation efficiency. Compared to the lithium niobate sources, they are more feasible, thanks to the easier manufacturing and the longer pump wavelength. They can produce intense, nearly single-cycle THz pulses at higher frequencies. With 20 mJ pumping at 1.8 µm wavelength, 45 µJ THz energy, and 17 MV/cm focused peak electric field can be expected at 3 THz phase matching frequency from the transmissive nonlinear echelon slab setup consisting of a 4 mm thick structured plan-parallel gallium phosphide crystal.

Effects of regular sport activities on stress level in sporting and non-sporting university students.

Background: Regular sport has favourable influence on the physical and mental state. Our aim was to analyse the relationship between regular sport activities, body parameters, cortisol level, perceived stress and the frequency of psychosomatic symptoms in male and female university students. Methods: Subjects were university students (N = 200). They were divided in sporting (more than 7 h week-1: 56 males (sm), 50 females (sf)) and non-sporting (less than 3 h week-1: 44 males (nsm) and 50 females (nsf)) groups. Body composition was estimated by Inbody720-analyser. Stress levels were measured by (1) free cortisol level in saliva measured by using IBL-ELISA kits and (2) questionnaires about psychosomatic symptoms and perceived stress scale. Results: There were significant subgroup' differences in body composition (fat%:sm:12.1 ± 6.0 vs. nsm:17.9 ± 6.8; sf:20.8 ± 5.5 vs. nsf:25.4 ± 5.7; muscle%:sm:50.3 ± 3.6 vs. nsm:47.6 ± 3.9; sf:43.8 ± 3.2 vs. nsf:41.7 ± 3.3), and in stress level (total scores:sm:21.0 ± 5.7 vs. nsm:23.3 ± 7.2; sf:25.5 ± 7.0 vs. nsf:28.0 ± 9.7). There were gender differences in the psychosomatic symptoms' frequency (total scores: sm: 14.6 ± 6.3 vs. sf: 20.4 ± 7.4; nsm: 14.9 ± 6.1 vs. nsf: 19.6 ± 8.2). The sporting students had larger muscle, smaller fat percentages, and lower level of stress. Basic level of salivary cortisol revealed significant relation with physical activity: sporting students had lower level of cortisol. This relation was reflected in higher percentage of students with low level of cortisol in the physically active subgroups (s/ns males: 29% vs. 15%; s/ns females: 18% vs. 5%) and in the higher percentage of female students with high level of cortisol in the non-sporting subgroup (27% vs. 11%). Conclusion: Regular sport activity is positively related with lower stress levels in university students.

Astrology in the crossfire: the stormy debate after the comet of 1577.

The new star of 1572 and the comet of 1577 had a major impact on the ways in which astronomical research developed in the late sixteenth and early seventeenth centuries. Behind this gradual but significant change there was an extended epistemological reform which placed increasing emphasis on reason and experience and strove to exclude arguments from Scripture and authority from scientific debate. This paper argues that the humanist debate on astrology after 1577, which was initiated by highly prestigious members of a supraconfessional Republic of Letters, can be seen as an element of this process. Unlike earlier detractors of astrology, these new critics chiefly employed philosophical and scientific arguments concerning the legitimation of the entire art. By analysing a variety of accounts, this paper will reveal how great and complex the stakes in the debate over astrology were. They concerned not only the crucial problem of predestination and God's interventionalism (hence also the possibility of miracles), but also the idea of science, the concept of the human mind, and ultimately the humanist ideal of the virtuous, rational, and responsible citizen.

Uniformly scalable lithium niobate THz pulse source in transmission geometry.

A novel THz source, based on optical rectification in LiNbO3 using the tilted-pulse-front technique, is proposed and experimentally demonstrated. The pulse-front tilt is introduced by a volume phase holographic grating, efficiently used at perpendicular incidence in transmission, and the THz pulses are produced in a LiNbO3 plane-parallel nonlinear echelon slab, arranged parallel to the grating. As a unique feature, the entire setup has a plane-parallel, transmission-type configuration, which straightforwardly enables distortion-free scaling to large sizes, high pulse energies and high THz field strengths. The possibility of operating the setup at cryogenic temperature for increased THz generation efficiency is also investigated. Calculations predict efficiencies of 95% for diffraction and 2% for THz generation at room temperature with a refractive-index-matching liquid between the grating and the echelon slab.

Comparison of the Cardiovascular Effects of Extreme Psychological and Physical Stress Tests in Male Soccer Players.

BACKGROUND: The purpose of our study was to compare the physiological effects of extreme physical and psychological stress tests in male soccer players, since these two types of stress apply to athletes with high performance requirements. METHODS: A total of 63 healthy male soccer players participated in this study, all of whom underwent both of the tests. A physical stress test was carried out in an exercise physiology laboratory, where subjects completed an incremental treadmill running test to full exhaustion, and a psychological test was performed in a military tactical room, where subjects met a street offence situation. Heart rate variability (HRV) and blood pressure (BP) were recorded directly before, immediately after, and 30 min after the stress tests. RESULTS: The majority of HRV indices changed significantly in both stress protocols. Inverse, significant changes (positive for the physical test, negative for the psychological test, p < 0.001) were found when comparing the alterations of HRV indices between the tests. Significant differences were found in the changes in systolic (p = 0.003) and diastolic (p < 0.001) BP between the test protocols, and also between the baseline and post-test measurements (p < 0.001). CONCLUSION: Both HRV and BP are sensitive physiological parameters to measure the impact of extreme physical and/or psychological stress.

Bone characteristics and physical fitness in children and adolescents with visual impairment.

BACKGROUND: Lower habitual physical activity in adolescents with visual impairment (VI) have detrimental effect on their general health such as bone quality and physical fitness. The aim of this study was to demonstrate the bone quality in children with VI and to analyze the correlations of their bone characteristics with anthropometric and physical fitness tests. METHODS: The participants (N.=38) were adolescents (14.85±2.79 yrs) with low vision (N.=18) or blindness (N.=20). Dual-energy X-ray absorptiometry (DEXA) was used to measure bone mineral density (BMD), bone mineral content (BMC) of the total body and L1-L4 of the lumbar spinal region. After anthropometry physical fitness was examined by laboratory test (V̇O2peak) and field tests (strength and running). RESULTS: Height, weight, Body Mass Index (BMI), V̇O2peak were similar in the two groups. Blind boys showed significant higher handgrip strength. Estimated V̇O2peak (from 20-m shuttle running test) was significantly lower in blind children (43.84±4.42 mL/kg/min) than in children with low vision (35.08±5.23 mL/kg/min; P<0.001). BMD and BMC did not differ in subgroups, Z-score of total body BMD was significantly lower in blind children. Means of Z-score in L1-L4 lumbal spinal region were negative values and similar in blind and low vision adolescents' subgroups. A linear regression model in the collective group revealed significant associations of BMD (r2=0.538; P=0.0001) and BMC (r2=0.698; P=0.048) with BMI and handgrip strength test. CONCLUSIONS: Adolescents with VI have generally decreased bone health and physical fitness level. BMI and handgrip strength are predictors of total body BMD and BMC; suggesting that these measures may be adequate to estimate bone health.

The MCT1 gene Glu490Asp polymorphism (rs1049434) is associated with endurance athlete status, lower blood lactate accumulation and higher maximum oxygen uptake.

The purpose of this study was to explore the association of the MCT1 gene Glu490Asp polymorphism (rs1049434) with athletic status and performance of endurance athletes. A total of 1,208 Brazilians (318 endurance athletes and 890 non-athletes) and 867 Europeans (315 endurance athletes and 552 non-athletes) were evaluated in a case-control approach. Brazilian participants were classified based on self-declared ethnicity to test whether the polymorphism was different between Caucasians and Afro-descendants. Moreover, 66 Hungarian athletes underwent an incremental test until exhaustion to assess blood lactate levels, while 46 Russian athletes had their maximum oxygen uptake ( V ⋅ O 2 max ) compared between genotypes. In the Brazilian cohort, the major T-allele was more frequent in Caucasian top-level competitors compared to their counterparts of lower competitive level (P = 0.039), and in Afro-descendant athletes compared to non-athletes (P = 0.015). Similarly, the T-allele was more frequent in European athletes (P = 0.029). Meta-analysis of the Brazilian and European cohorts confirmed that the T-allele is over-represented in endurance athletes (OR: 1.48, P = 0.03), especially when Afro-descendant athletes were included in the meta-analysis (OR: 1.58, P = 0.005). Furthermore, carriers of the T/T genotype accumulated less blood lactate in response to intense effort (P < 0.01) and exhibited higher V ⋅ O 2 max (P = 0.04). In conclusion, the Glu490Asp polymorphism was associated with endurance athletic status and performance. Our findings suggest that, although ethnic differences may exist, the presence of the major T-allele (i.e., the Glu-490 allele) favours endurance performance more than the mutant A-allele (i.e., the 490-Asp allele).

Physiological and Psychological Responses to a Maximal Swimming Exercise Test in Adolescent Elite Athletes.

BACKGROUND: Continuously rising performances in elite adolescent athletes requires increasing training loads. This training overload without professional monitoring, could lead to overtraining in these adolescents. METHODS: 31 elite adolescent athletes (boys: n = 19, 16 yrs; girls: n = 12, 15 yrs) participated in a field-test which contained a unified warm-up and a 200 m maximal freestyle swimming test. Saliva samples for testosterone (T) in boys, estradiol (E) in girls and cortisol (C) in both genders were collected pre-, post- and 30 min post-exercise. Lactate levels were obtained pre- and post-exercise. Brunel Mood Scale, Perceived Stress Scale and psychosomatic symptoms questionnaires were filled out post-exercise. RESULTS: Lactate levels differed between genders (boys: pre: 1.01 ± 0.26; post: 8.19 ± 3.24; girls: pre: 0.74 ± 0.23; post: 5.83 ± 2.48 mmol/L). C levels increased significantly in boys: pre- vs. post- (p = 0.009), pre- vs. 30 min post-exercise (p = 0.003). The T level (p = 0.0164) and T/C ratio (p = 0.0004) decreased after field test which draws attention to the possibility of overtraining. Maximal and resting heart rates did not differ between genders; however, heart rate recovery did (boys: 29.22 ± 7.4; girls: 40.58 ± 14.50 beats/min; p = 0.008). CONCLUSIONS: Our models can be used to explain the hormonal ratio changes (37.5-89.8%). Based on the results this method can induce hormonal response in elite adolescent athletes and can be used to notice irregularities with repeated measurements.

Lithium niobate and lithium tantalate based scalable terahertz pulse sources in reflection geometry.

A new type of THz source, working in reflection geometry, is proposed, where the pulse-front-tilt is introduced by a periodically micro-structured metal profile. For optical coupling, high refractive index nanocomposite fluid is used between the nonlinear optical material and the structured metal surface. Numerical simulations predict ∼87 and ∼85% optimized diffraction efficiencies for lithium niobate and lithium tantalate at 1030 and 800 nm pump wavelengths. The largest diffraction efficiencies can be achieved for a larger refractive index of the nanocomposite fluid than the index of the nonlinear material, for both cases. THz generation efficiencies of ∼3 and ∼1% are predicted for lithium niobate and lithium tantalate, respectively.

Single-cycle scalable terahertz pulse source in reflection geometry.

A tilted-pulse-front pumped terahertz pulse source is proposed for the generation of extremely high field single-cycle terahertz pulses. The very simple and compact source consists of a single crystal slab having a blazed reflection grating grooved in its back surface. Its further important advantages are the energy scalability and the symmetric THz beam profile. Generation of ∼50 MV/cm focused field with 10.8 mJ terahertz pulse energy is predicted for a 7 cm diameter LiNbO 3 crystal, if the pump pulse is of 870 mJ energy, 1030 nm central wavelength and 1 ps pulse duration. Such sources can decisively promote the realization of THz driven electron and proton accelerators and open the way for a new generation concept of terahertz pulses having extreme high field.

Numerical investigation of imaging-free terahertz generation setup using segmented tilted-pulse-front excitation.

Recently a hybrid-type terahertz (THz) pulse source was proposed for high energy terahertz pulse generation. It is the combination of the conventional tilted-pulse-front setup and a nonlinear crystal with a transmission stair-step echelon of period in the hundred-micrometer range etched into the front face. The tilt angle introduced by the conventional tilted-pulse-front setup (pre-tilt) was chosen to be equal to the tilt-angle needed inside the nonlinear crystal (62° for lithium niobate (LN)) in order to fulfill velocity-matching. In this case, plane-parallel nonlinear optical crystals can be used. The possibility of using a plane-parallel nonlinear optical crystal for producing good-quality, symmetric THz beams was considered the most important advantage of this setup. In the present paper, a thorough numerical investigation of a modified version of that setup is presented. In the new version, the tilted pulse-front is created by a transmission grating without any imaging optics, and a wedged nonlinear optical crystal with a small wedge angle is supposed. According to a 1D numerical code, significantly higher THz generation efficiency can be achieved with a transmission stair-step echelon-faced nonlinear crystal having a 5 - 15-degree wedge angle than with a plane-parallel one or with the conventional tilted-pulse-front setup. Because of the spatially-dependent group-delay dispersion introduced by the transmission grating, a small wedge in the nonlinear crystal improves the spatial homogeneity of the THz-generation process, resulting in higher efficiencies and better beam profiles. At 100 K temperature, and by using 800 nm pump pulses with 20 mJ pulse energy, 100 fs pulse length and 8 mm beam spot radius, approximately 4.5% conversion efficiency and close to 1 mJ terahertz pulse energy can be reached with the newly-proposed setup.

Demonstration of a tilted-pulse-front pumped plane-parallel slab terahertz source.

A new type of tilted-pulse-front pumped terahertz (THz) source has been demonstrated, which is based on a LiNbO3plane-parallel slab with an echelon structure on its input surface. Single-cycle pulses of 1 µJ energy and 0.30 THz central frequency have been generated with 5×10-4 efficiency from such a source. One order-of-magnitude increase in efficiency is expected by pumping a cryogenically cooled echelon of increased size and thickness with a Ti:sapphire laser. The use of a plane-parallel nonlinear optical crystal slab enables straightforward scaling to high THz pulse energies and the production of a symmetric THz beam with a uniform pulse shape for good focusability and high field strength.

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 hundred-micrometer 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 stair-step 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.

Velocity matching by pulse front tilting for large area THz-pulse generation.

We propose a generally applicable velocity matching method for THz-pulse generation by optical rectification in the range below the phonon frequency of the nonlinear material. Velocity matching is based on pulse front tilting of the ultrashort excitation pulse and is able to produce a large area THz beam. Tuning of the THz radiation by changing the tilt angle is experimentally demonstrated for a narrow line in the range between 0.8- 0.97 times the phonon frequency. According to model calculations broadband THz radiation can be generated at lower frequencies. Advantages of the new velocity matching technique in comparison to the electro-optic Cherenkov effect and non-collinear beam mixing are discussed.