RESUMEN
The development and technological applications of molecular spin systems require versatile experimental techniques to characterize and control their static and dynamic magnetic properties. In the latter case, bulk spectroscopic and magnetometric techniques, such as AC magnetometry and pulsed electron paramagnetic resonance, are usually employed, showing high sensitivity, wide dynamic range, and flexibility. They are based on creating a nonequilibrium state either by changing the magnetic field or by applying resonant microwave radiation. Another possible source of perturbation is a laser pulse that rapidly heats the sample. This approach has proven to be one of the most useful techniques for studying the kinetics and mechanism of chemical and biochemical reactions. Inspired by these works, we propose an inductive detection of temperature-induced magnetization dynamics as applied to the study of molecular spin systems and describe the general design and construction of a particular induction probehead, taking into account the constraints imposed by the cryostat and electromagnet. To evaluate the performance, several coordination compounds of VO2+, Co2+, and Dy3+ were investigated using low-energy pulses of a terahertz free electron laser of the Novosibirsk free electron laser facility as a heat source. All measured magnetization dynamics were qualitatively or quantitatively described using a proposed basic theoretical model and compared with the data obtained by alternating current magnetometry. Based on the results of the research, the possible scope of applications of inductive detection and its advantages and disadvantages in comparison with standard methods are discussed.
RESUMEN
The development of efficient and reliable sensors operating at room temperature is essential to advance the application of terahertz (THz) science and technology. Pyroelectric THz detectors are among the best candidates, taking into account their variety, outstanding performance, ease of fabrication, and robustness. In this work, we compare the performance of six different detectors, based on either LaTiO3 crystal or different polymeric films, using monochromatic radiation of the Novosibirsk Free Electron Laser facility (NovoFEL) in the frequency range of 0.9-2.0 THz. The main characteristics, including noise equivalent power and frequency response, were determined for all of them. Possible reasons for the differences in the obtained characteristics are discussed on the basis of the main physicochemical characteristics and optical properties of the sensitive area. At least three detectors showed sufficient sensitivity to monitor the shape and duration of the THz macropulses utilizing only a small fraction of the THz radiation from the primary beam. This capability is crucial for accurate characterization of THz radiation during the main experiment at various specialized endstations at synchrotrons and free electron lasers. As an example of such characterization, the typical stability of the average NovoFEL radiation power at the beamline of the electron paramagnetic resonance endstation was investigated.
RESUMEN
The Novosibirsk Free Electron Laser (NovoFEL) facility is able to produce high-power tunable terahertz (THz) laser radiation in quasi-continuous mode. The ability to control/shape this THz radiation is required in a number of user experiments. In this work we propose a modulation approach suitable for free electron lasers based on recuperation design. It allows for generating THz macropulses of a desirable length, down to several microseconds (limited by a quality factor of FEL optical resonator). Using this approach, macropulses in the time window from several microseconds to several hundred microseconds have been shown for three possible frequency ranges: mid-infrared (~1100 cm-1), far-infrared (~200 cm-1) and THz (~40 cm-1). In each case, the observed rise and decay of the macropulse have been measured and interpreted. The advantage of using short macropulses at the maximum peak power available has been demonstrated with the time-resolved Electron Paramagnetic Resonance (EPR) spectroscopy.
RESUMEN
Electron Paramagnetic Resonance (EPR) station at the Novosibirsk Free Electron Laser (NovoFEL) user facility is described. It is based on X-band (â¼9â¯GHz) EPR spectrometer and operates in both Continuous Wave (CW) and Time-Resolved (TR) modes, each allowing detection of either direct or indirect influence of high-power NovoFEL light (THz and mid-IR) on the spin system under study. The optics components including two parabolic mirrors, shutters, optical chopper and multimodal waveguide allow the light of NovoFEL to be directly fed into the EPR resonator. Characteristics of the NovoFEL radiation, the transmission and polarization-retaining properties of the waveguide used in EPR experiments are presented. The types of proposed experiments accessible using this setup are sketched. In most practical cases the high-power radiation applied to the sample induces its rapid temperature increase (T-jump), which is best visible in TR mode. Although such influence is a by-product of THz radiation, this thermal effect is controllable and can deliberately be used to induce and measure transient signals of arbitrary samples. The advantage of tunable THz radiation is the absence of photo-induced processes in the sample and its high penetration ability, allowing fast heating of a large portion of virtually any sample and inducing intense transients. Such T-jump TR EPR spectroscopy with THz pulses has been previewed for the two test samples, being a useful supplement for the main goals of the created setup.