Relativistic electron bunches circulating in accelerators are subjected to a dynamical instability leading to microstructures at millimeter to centimeter scale. Although this is a well-known fact, direct experimental observations of the structures, or the field that they emit, remained up to now an open problem. Here, we report the direct, shot-by-shot, time-resolved recording of the shapes (including envelope and carrier) of the pulses of coherent synchrotron radiation that are emitted, and that are a "signature" of the electron bunch microstructure. The experiments are performed on the UVSOR-III storage ring, using electrical field sensitive YBa2Cu3O(7-x) thin-film ultrafast detectors. The observed patterns are subjected to permanent drifts, that can be explained from a reasoning in phase space, using macroparticle simulations.

High-Tc thin-film YBa2Cu3O7-x (YBCO) detectors were deployed for the real-time observation of Coherent Synchrotron Radiation (CSR). Due to enhanced fabrication techniques enabling the patterning of sub-μm sized detector areas responsivity values as high as 1V/pJ for pulsed THz excitations have been achieved at the ANKA synchrotron facility at the Karlsruhe Institute of Technology (KIT). Response of the detectors is linear over the whole dynamic range of the IR1 beamline. Combining the picosecond scaled response mechanism of the high-temperature superconductor YBa2Cu3O7-x (YBCO) to THz excitations with broad-band readout a temporal resolution of 15 ps full width at half maximum (FWHM) was reached. Real-time resolution of CSR single shots was observed at ANKA and UVSOR-III, the synchrotron facility of the Institute of Molecular Science in Okazaki, Japan.

We use an ultrafast NbN superconducting detector to investigate dynamic bulk heat-storage effects in a THz QCL. A first-order heat-accumulation model is used to obtain reliable estimates of the thermal resistance and heat capacity from the measured temperature variation.

We present a study of the response to pulsed infrared radiation of Fe layer shunted pnictide thin film microstructures. The thin film multilayer consisting of 20-nm-thick Fe buffer, 50-nm-thick Ba(Fe, Co)2As2 film, and gold protection layer were deposited on heated MgO and MgAl2O4 substrates by pulsed-laser deposition. The multilayers were patterned into 5- to 8-μm-wide and 5-μm-long microbridges by electron-beam lithography and ion-milling technique. The microbridges show Tc ≈ 20 K and a critical current density up to 2.56 MA/cm2 at T = 10 K. The photo-response of Fe-shunted Ba(Fe, Co)2As2 thin film microbridges to infrared radiation was studied in a wide range of incident optical power, operation temperature, and bias current. We have found that the electron energy relaxation in studied multilayers is dependent on substrate material and is 1.75 times faster in the case of MgAl2O4 characterized by lattice matching to the pnictide film in comparison to the MgO substrate.

High-temperature superconducting YBa 2 Cu 3 O 7 - δ (YBCO) thin-film detectors with improved responsivities were developed for fast time-domain measurements in the THz frequency range. YBCO thin films of ≈ 30 nm thickness were patterned to micro- and nanobridges and embedded into planar log-spiral THz antennas. The YBCO thin-film detectors were characterized with continuous wave radiation at 0.65 THz. Responsivity values as high as 710 V/W were found for the YBCO nanobridges. Pulsed measurements in the THz frequency range were performed at the electron storage ring ANKA from the Karlsruhe Institute of Technology (KIT). Due to the high responsivities of the nanobridges no biasing was required for the detection of the coherent synchrotron radiation pulses achieving very good agreement between the measured pulse shapes and simulations.

We report the time-domain analysis of fast pulses emitted by a quantum cascade laser (QCL) operating at ~ 3.1 THz using superconducting THz detectors made from either NbN or YBa 2 Cu 3 O 7-δ (YBCO) thin films. The ultrafast response from these detectors allows resolution of emission features occurring on a nanosecond time-scale, which is not possible with commercially available Ge or InSb bolometers owing to their much larger time constants. We demonstrate that the time-dependent emission can be strongly affected by relatively small variations in the driving pulse. The QCL output power-current relationship was determined, based on correlation of the time-dependent emission of radiation with current flow in the QCL, under different QCL bias conditions. We show that this relationship differs from that obtained using bolometric detectors that respond only to the integrated pulse energy. The linearity of the detectors, and their agreement with measurements using a Ge bolometer, was also established by studying the QCL emission as a function of bias voltage and excitation pulse length. This measurement scheme could be readily applied to the study of ultrafast modulation and mode-locking of THz-QCLs.

In the low-alpha operation mode of the ANKA synchrotron light source, coherent synchrotron radiation (CSR) is emitted from short electron bunches. Depending on the bunch current, the radiation shows bursts of high intensity. These bursts of high intensity THz radiation display a time evolution which can be observed only on long time scales with respect to the revolution period. In addition, long range wake fields can introduce a correlation between the bunches within a bunch train and thus modify the observed behaviour. A novel detection system consisting of an ultra-fast superconducting THz detector and data acquisition system was used to investigate correlations visible on the bursting pattern and to study the interactions of very short pulses in the ANKA storage ring.

Joule heating causes significant degradation in the power emitted from terahertz-frequency quantum-cascade lasers (THz QCLs). However, to date, it has not been possible to characterize the thermal equilibration time of these devices, since THz power degradation over sub-millisecond time-scales cannot be resolved using conventional bolometric or pyroelectric detectors. In this letter, we use a superconducting antenna-coupled niobium nitride detector to measure the emission from a THz QCL with a nanosecond-scale time-resolution. The emitted THz power is shown to decay more rapidly at higher heat-sink temperatures, and in steady-state the power reduces as the repetition rate of the driving pulses increases. The pulse-to-pulse variation in active-region temperature is inferred by comparing the THz signals with those obtained from low duty-cycle measurements. A thermal resistance of 8.2 ± 0.6 K/W is determined, which is in good agreement with earlier measurements, and we calculate a 370 ± 90-μs bulk heat-storage time, which corresponds to the simulated heat capacity of the device substrate.

In order to improve the frequency-division multiplexing (FDM) in transition edge sensor (TES) imaging arrays, it is suggested to replace commonly used SQUID amplifiers with a semiconductor high-frequency cooled amplifier. This would result in a single 10-GHz bandwidth amplifier serving the array of more than 1000 detectors. The basic idea is to implement an antenna-coupled TES as a load for a high-Q resonator, weakly coupled to a microwave transmission line. This high-frequency scheme substitutes the traditional wire connections to the TES. The NEP as low as 2×10-19 W/Hz0.5 is estimated at ambient temperature of 300 mK for submicron-size TES absorber made of Ti; the NEP is limited by 3 K noise temperature of the amplifier. To verify the new concept, prototype TES devices made of Nb are developed and tested above 4 K. The NEP of about 1.5×10-15 W/Hz0.5 is estimated for the experimental micron-size prototype devices made of Nb at 4.5 K. The IV -curves of the TES at different temperatures are recovered using the RF and heat balance models along with the experimental R(T) data; presence of the negative electrothermal feedback is verified.

We report on the development of room temperature THz bolometers made from semiconducting PrBa 2 Cu 3 O 7-δ (PBCO) thin films on MgO substrate. PBCO thin films show a high temperature coefficient of resistance (TCR ≈ 1-2%/K) at low resistivity values (ρ ≈ 2000 μΩcm) in comparison to other semiconducting materials like amorphous silicon or vanadium oxide. A low resistivity enables efficient coupling to an integrated planar antenna required to couple THz radiation to micrometer sized detector elements. A detailed electrical characterization as well as radiation measurements at 0.65 THz of the 70-100 nm thick PBCO film microbridges embedded into log-spiral planar antennas have been performed. An electrical responsivity up to S =33 V/W and a noise equivalent power of NEP=1.52×10 -10 W/√Hz at a modulation frequency of 10 kHz limited by the measurement setup have been achieved.

A high-speed YBa 2 Cu 3 O 7-δ direct detection system was developed to monitor terahertz picosecond pulses in the time domain. High-T C superconducting thin-film YBa 2 Cu 3 O 7-δ microbridges with critical temperatures of T C = 85 K were embedded into a planar log-spiral antenna to couple the broadband terahertz radiation (0.1 -2 THz) of several picosecond pulsed sources. The YBa 2 Cu 3 O 7-δ detectors were installed in a liquid nitrogen cryostat equipped with 18 GHz effective bandwidth readout electronics. THz pulses generated at the electron storage rings ANKA and UVSOR-II have been resolved with a temporal resolution of 30 ps (full width at half maximum) limited by the readout electronics bandwidth. Beam dynamic effects of bursting coherent synchrotron radiation were successfully monitored.

The temporal evolution of picosecond THz pulses generated at ANKA, the electron storage ring of the Karlsruhe Institute of Technology, has been measured in real-time using an ultra-fast YBa2Cu3O7−δ detection system. YBa2Cu3O7−δ thin-film detectors with 30 nm thickness were patterned to microbridges (2 μm long, 4.5 μm wide) and embedded into a planar log-spiral THz antenna. The detectors were glued on a silicon lens and installed in an ultra-fast readout system with a temporal resolution of 15 ps (full width at half maximum). Detector responses as short as 17 ps were recorded showing very good agreement with the expected storage ring bunch lengths.