A bottleneck for the investigation of electron beam dynamics in ring accelerators is a fast detection scheme coping with their high repetition rates in the MHz range. For example, at KARA (KArlsruhe Research Accelerator), the electron storage ring at the Karlsruhe Institute of Technology (KIT) in Germany, we showed that electro-optical methods enable single-shot detection of longitudinal electron bunch profiles by imprinting them onto chirped laser pulses. However, commercial cameras required to detect the spectra are typically limited to hundreds of kHz in readout speed. To tackle these challenges, we developed KALYPSO (KArlsruhe Linear array detector for MHz-rePetition rate SpectrOscopy), a linear detector array with a data acquisition system (DAQ) allowing high data-rates over long time scales. Due to a modular approach, various sensors (InGaAs and Si) can be used, so that KALYPSO can be adapted to different experiments with spectral regimes ranging from near-ultraviolet (NUV) to near-infrared (NIR). In this talk, we present recent results on studies of longitudinal and horizontal bunch profiles using KALYPSO. As an outlook, we give another example for MHz-range readout using KALYPSO, namely horizontal bunch profile diagnostics measuring the radiation emitted from a dispersive section in a storage ring. At the KARA visible light diagnostics (VLD) port the emitted radiation above 400 nm was previously recorded with a fast-gated camera. Here, limitations are the repetition rate in combination with the huge number of cycles during continuous measurements. To overcome these limitations, KALYPSO can repleace the fast-gated camera. Furthermore, due to the easy implementation of KALYPSO, we envision numerous applications for table-top experiments as well as for large-scale facilies.
KALYPSO is a novel detector operating at line rates above 10 Mfps. The detector board holds a silicon or InGaAs linear array sensor with spectral sensitivity ranging from 400 nm to 2600 nm. The sensor is connected to a cutting-edge, custom designed, ASIC readout chip, which is responsible for the remarkable frame rate. The FPGA readout architecture enables continuous data acquisition and processing in real time. This detector is currently employed in many synchrotron facilities for beam diagnostics and for the characterization of self-built Ytterbium-doped fiber laser emitting around 1050 nm with a bandwidth of 40 nm.
KALYPSO is a novel detector operating at line rates above 10 Mfps. It consists of a detector board connected to FPGA based readout card for real time data processing. The detector board holds a Si or InGaAs linear array sensor, with spectral sensitivity ranging from 400 nm to 2600 nm, which is connected to a custom made front-end ASIC. A FPGA readout framework performs the real time data processing. In this contribution, we present the detector system, the readout electronics and the heterogeneous infrastructure for machine learning processing. The detector is currently in use at several synchrotron facilities for beam diagnostics as well as for single-pulse laser characterizations. Thanks to the shot-to-shot capability over long time scale, new attractive applications are open up for imaging in biological and medical research.
We have set-up a scanning near-field infrared microscope (SNIM) with widely tunable lasers for label-free molecule
identification by infrared spectral fingerprints. The lateral resolution is as low as 30 nm corresponding to the
nanotip curvature radius. We obtained infrared spectra from nanoscale sections of self-assembled monolayers
(SAM) with volumes as small as 0.01 attoliter corresponding to less than 30000 molecules. Spectroscopy of
lipid bilayer stacks on mica revealed nanoscale near-field depth resolution of 80 to 120 nm. We discuss combined
systems of membrane proteins and lipids on SAM supports approaching cell like membrane structures. We report
on the progress of the set-up of an infrared and terahertz near-field microscope for the new synchrotron beam
line at ANKA for full spectral nanoscale information retrieval.
Liquid water is a very strong absorber in the THz frequency range. We have set-up a unique germanium
laser spectrometer consisting of a Ge:Be laser, tunable from 1 to 4 THz, and a sensitive Ge photoconductor
detector. The spectrometer uses a measurement scheme alternating sample and reference signal while placed in
an environmentally controlled housing for high stability of temperature and humidity. The laser system leads to a
very small statistical error in the absolute absorption coefficient (400-500 cm-1) of less than 0.1% corresponding
to 0.3 cm-1 while systematic errors due to filling of the sample cells become dominant. The high accuracy allows
us to systematically investigate the effects of different solvates on water dynamics. Even a single point mutation
in a protein can be measured in the THz absorption coefficient in the spectral range from 2 to 3 THz. The system
has been recently used to study various solvates in liquid water like sugars and prototype proteins in aqueous
buffer solutions in dependence of temperature, pH values, and denaturants. These studies are now augmented
by time-resolved measurements using THz time-domain spectroscopy to analyze the kinetics of protein folding.
We also discuss other THz sources and detection methods including the investigation of coherent synchrotron
radiation at the synchrotron ANKA in Karlsruhe.
Semiconductor based terahertz sources and lasers allow applications in biomolecular spectroscopy and imaging.
We present typical experimental set-ups to study liquid and water samples. Water has a very high absorption
coefficient in the THz spectral range. It can be measured in transmission if a high signal-to-noise ratio is available
otherwise by reflection measurements. We show THz imaging examples of dried lactalbumin drops and a THz
spectrum of a thin film of the nucleobase guanine.
Germanium terahertz (THz) lasers based on a heavy hole-light hole population inversion within the valence bands show strong promise for widespread applications due to their unparalleled frequency tuning range and high output power up to several Watts. Germanium lasers have attractive laser properties: tunability from 1 to 4 THz, high finesse of 106 with line widths below 1 MHz and linear polarization. Laser operation is possible with small mm- sized permanent magnets and closed-cycle refrigeration. Since 1995 we have increased the duty cycle (laser on-time) of such lasers from 10-5 up to 2.5 X 10-2 (2.5%). We report on our current research efforts aimed at achieving continuous wave emission. These efforts include a reduction of the active laser crystal volume from typical values of 30 - 60 mm3 to and perhaps below 1 mm3 and materials and electric field homogeneity improvements to enhance the conversion efficiency. A planar contact geometry is suggested to allow improved heat sinking. Our planned applications include but are not limited to airborne and satellite based research for the study of molecules in the upper atmosphere or in star-forming regions of the universe.
The Institute of Space Sensor Technology of the German Aerospace Center (DLR) is developing a heterodyne array receiver for the frequency range 2 to 6 THz for the Stratospheric Observatory for Infrared Astronomy (SOFIA). Key science issues in that frequency range are the observation of lines of atoms [e.g. (OI)], ions [e.g. (CII), (NII)], and molecules (e.g. OH, HD, CO) with high spectral resolution to study the dynamics and evolution of galactic and extragalactic objects. Long term goal is the development of an integrated array heterodyne receiver with superconducting hot electron bolometric (HEB) mixers and p-type Ge or Si lasers as local oscillators. The first generation receiver will be composed of HEB mixers in a 2 pixel 2 polarization array which will be pumped by a gas laser local oscillator. Improved Schottky diode mixers are the backup solution for the HEBs. The state of the art of HEB mixer and p-type Ge laser technology are described as well as possible improvements in the 'conventional' optically pumped far-infrared laser and Schottky diode mixer technology. Finally, the frequency coverage of the first generation heterodyne receiver for some important astronomical transitions is discussed. The expected sensitivity is compared to line fluxes measured by the ISO satellite.
Heterodyne mixing of the p-Ge laser and a FIR ring laser at 117.7 pm (CH2F2) and 118.8 pm (CH3OH) revealed the mode structure, the absolute linewidth and a frequency tunability of 25 MHz during the p-Ge laser pulse.