RESUMO
We have developed a single-shot terahertz time-domain spectrometer to perform optical-pump/terahertz-probe experiments in pulsed, high magnetic fields up to 30 T. The single-shot detection scheme for measuring a terahertz waveform incorporates a reflective echelon to create time-delayed beamlets across the intensity profile of the optical gate beam before it spatially and temporally overlaps with the terahertz radiation in a ZnTe detection crystal. After imaging the gate beam onto a camera, we can retrieve the terahertz time-domain waveform by analyzing the resulting image. To demonstrate the utility of our technique, we measured cyclotron resonance absorption of optically excited carriers in the terahertz frequency range in intrinsic silicon at high magnetic fields, with results that agree well with published values.
RESUMO
We have performed terahertz time-domain magnetospectroscopy by combining a rapid scanning terahertz time-domain spectrometer based on the electronically controlled optical sampling method with a table-top minicoil pulsed magnet capable of producing magnetic fields up to 30 T. We demonstrate the capability of this system by measuring coherent cyclotron resonance oscillations in a high-mobility two-dimensional electron gas in GaAs and interference-induced terahertz transmittance modifications in a magnetoplasma in lightly doped n-InSb.
RESUMO
We have developed a mini-coil pulsed magnet system with direct optical access, ideally suited for nonlinear and ultrafast spectroscopy studies of materials in high magnetic fields up to 30 T. The apparatus consists of a small coil in a liquid nitrogen cryostat coupled with a helium flow cryostat to provide sample temperatures down to below 10 K. Direct optical access to the sample is achieved with the use of easily interchangeable windows separated by a short distance of ~135 mm on either side of the coupled cryostats with numerical apertures of 0.20 and 0.03 for measurements employing the Faraday geometry. As a demonstration, we performed time-resolved and time-integrated photoluminescence measurements as well as transmission measurements on InGaAs quantum wells.
RESUMO
Gender verification of female athletes has long been criticized by geneticists, endocrinologists, and others in the medical community. Problems include invalid screening tests, failure to understand the problems of intersex, the discriminatory singling out of women based only on laboratory results, and the stigmatization and emotional trauma experienced by individuals screened positive. Genuine sex-impostors have not been uncovered by laboratory-based genetic testing; however, gender verification procedures have resulted in substantial harm to a number of women athletes born with relatively rare genetic abnormalities. Individuals with sex-related genetic abnormalities raised as females have no unfair physical advantage and should not be excluded or stigmatized, including those with 5-alpha-steroid-reductase deficiency, partial or complete androgen insensitivity, and chromosomal mosaicism. In 1990, the International Amateur Athletics Federation (IAAF) called for ending genetic screening of female athletes and in 1992 adopted an approach designed to prevent only male impostors from competing. The IAAF recommended that the "medical delegate" have the ultimate authority in all medical matters, including the authority to arrange for the determination of the gender of the competitor if that approach is judged necessary. The new policy advocated by the IAAF, and conditionally adopted by the International Olympic Committee, protects the rights and privacy of athletes while safeguarding fairness of competition, and the American Medical Association recommends that it become the permanent approach.