Ultrafast High-Field THz beamline at X-ray FEL

THz sources at FLASH utilize spent electron beam from a soft X-ray FEL to generate very intense (up to 150µJ), tunable frequency (1-300THz) and ultrafast narrowband (~10%) THz pulses, which are naturally synchronized to soft X-ray pulses [1]. This unique combination allows for wide range of element specific pump-probe experiments in physics, material science and biology. Here we discuss the unique features of the FLASH THz pulses and the accelerator source that bring along a set of challenges in the diagnostics of their key parameters: pulse energy, spectral, temporal and spatial profiles.VII International School and Conference on Photonics : PHOTONICA2019 : Abstracts of Tutorial, Keynote, Invited Lectures, Progress Reports and Contributed Papers; August 26-30; Belgrad

Femtosecond laser spectroscopy for exploration of space

Space agencies around the world have the exploration of solar system bodies in the focus of their activities for decades already. The search for traces of life and to a better understanding of the geology of planets, moons and asteroids motivates these explorations. Our (DLR institute for Optical Sensor Systems (DLR-OS)) contribution to this topic is the development of spectroscopic sensors for material identification. DLR-OS is developing a wide range of spectroscopic sensors that reach from passive infrared spectrometers for remote sensing employed on orbiters to active laser spectroscopies such as NIR spectroscopy, Raman spectroscopy or Laser-Induced Breakdown Spectroscopy that are employed on robotic lander missions. Space, weight and power restrictions as well as robustness against harsh environmental conditions are inherent prerequisites for space missions and lead to specific design solutions for these instruments. Driven by emerging technology of space ready short-pulsed (femtosecond) lasers [1,2], we are introducing the new topic of time domain spectroscopies to space exploration. In this work, we present our first results on coherent phonon and THz time domain spectroscopies on space relevant minerals.IX International School and Conference on Photonics : PHOTONICA2023 : book of abstracts; August 28 - September 1, 2023; Belgrad

Electron-impact excitation of the (5s(2)5p) P-2(1/2) -> (5s(2)6s) S-2(1/2) transition in indium: Theory and experiment

We present angle-integrated and angle-differential cross sections for electron-impact excitation of the (5s(2)5p) P-2(1/2) -> (5s(2)6s) S-2(1/2) transition in atomic indium. Experimental data for six incident electron energies between 10 and 100 eV are compared with predictions from semirelativistic and fully relativistic B-spline R-matrix calculations, as well as a fully relativistic convergent close-coupling model. Agreement between our measured and calculated data is, with a few exceptions, found to be typically very good. Additionally, the agreement between the present theoretical predictions is generally excellent, with the remaining small deviations being associated with the slightly different, although still very accurate, descriptions of the target structure. Agreement between the present results and an earlier relativistic distorted-wave computation [T. Das, R. Srivastava, and A. D. Stauffer, Phys. Lett. A 375, 568 (2011)] was, however, found to be marginal, particularly at 10 and 20 eV

Electron-impact excitation of the (5s25p) P1/2 2 (5s26s) S1/2 2 transition in indium: Theory and experiment

We present angle-integrated and angle-differential cross sections for electron-impact excitation of the (5s25p) 2 P1/2 -> (5s26s) 2 S1/2 transition in atomic indium. Experimental data for six incident electron energies between 10 and 100 eV are compared with predictions from semirelativistic and fully relativistic B-spline R-matrix calculations, as well as a fully relativistic convergent close-coupling model. Agreement between our measured and calculated data is, with a few exceptions, found to be typically very good. Additionally, the agreement between the present theoretical predictions is generally excellent, with the remaining small deviations being associated with the slightly different, although still very accurate, descriptions of the target structure. Agreement between the present results and an earlier relativistic distorted-wave computation.The work of K.R.H., O.Z., and K.B. was supported by the U.S. National Science Foundation under Grants No. OAC1834740 and No. PHY-1803844, and by the XSEDE supercomputer allocation Grant No. PHY-090031. The (D)BSR calculations were carried out on Stampede2 at the Texas Advanced Computing Center. The work of D.V.F. and I.B. was supported by the Australian Research Council and resources provided by the Pawsey Supercomputing Centre with funding from the Australian Government and the Government of Western Australia. F.B. and G.G. acknowledge partial financial support from the Spanish Ministry MICIU (Project No. PID2019-104727RB-C21) and CSIC (Project No. LINKA20085). This work was also financially supported, in part, by the Australian Research Council (Project No. DP180101655), the Ministry of Education, Science and Technological Development of the Republic of Serbia, and the Institute of Physics (Belgrade

Time-resolved luminescence spectra of greater celandine plant extract (

In this work, we analyze optical characteristics of greater celandine (Chelidonium majus L.) ethanol solution extracts and fresh leaf samples. Optical emission of samples was measured using a pulsed laser excitation of tunable wavelengths (320–470 nm) and time-resolved detection system. Results of our analysis reveal two distinct alkaloid optical emission bands with different excitation characteristics. Chlorophyll fluorescence emission band was also detected. Time-resolved analysis of luminescent spectra shows that lifetimes of both alkaloid fluorescence bands and chlorophyll band are in nanosecond domai

Orange-Reddish Light Emitting Phosphor GdVO4:Sm3+ Prepared by Solution Combustion Synthesis

The gadolinium vanadate doped with samarium (GdVO4:Sm3+) nanopowder was prepared by the solution combustion synthesis (SCS) method. After synthesis, in order to achieve the full crystallinity, the material was annealed in air atmosphere at 900°C. Phase identification in the postannealed powder samples was performed by X-ray diffraction, and morphology was investigated by high-resolution scanning electron microscopy (SEM). Photoluminescence characterization of the emission spectrum and time-resolved analysis have been performed using the tunable laser optical parametric oscillator excitation and the streak camera. Several strong emission bands in the Sm3+ emission spectrum were observed, located at 567 nm (4G5/2–6H5/2), 604 nm (4G5/2–6H7/2), and 646 (654) nm (4G5/2–6H9/2), respectively. The weak emission bands at 533 nm (4F3/2–6H5/2) and 706 nm (4G5/2–6H11/2) and a weak broad luminescence emission band of VO43− were also observed by the detection system. We analyzed the possibility of using the host luminescence for two-color temperature sensing. The proposed method is improved by introducing the temporal dependence in the line intensity ratio measurements

Photoacoustic elastic bending in thin film-substrate system: Experimental determination of the thin film parameters

The aim of this work is the development of photoacoustic (PA) method for the measurement and determination of parametres of thin films (with a thickness of less than 1 mu m). Experimental study of the optical, thermal, and elastic characteristics of the thin film on Si substrate by PA elastic bending method was given. Thin film-semiconductor (Si) sample is modeled by simultaneous analysis of the plasma, thermal, and elastic wave equations. Two normalization procedures of the PA elastic bending signal in function of the modulation frequency of the optical excitation were established. The experimental PA elastic bending signals were measured and analysed. Without loss of generality, the TiO2 thin film (with a thickness of 0.5 mu m) on Si substrate (circular plate) was experimentaly studied. We have studied the PA elastic bending signals in order to obtain the values of optical, thermal, and elastic parameters of TiO2 film. The analysis shows that it is possible to develop noncontact and nondestructive experimental method-PA elastic bending method for thin film study, with possibility to obtain the optical, thermal, and elastic parameters of the film thinner than 1 mu m

Study of Silicon Cantilevers by the Photoacoustic Elastic Bending Method

Rectangular silicon cantilevers are studied by the photoacoustic (PA) elastic bending method. Experimental signals versus modulation frequency of the excitation optical beam are measured and analyzed in a frequency range from 20 Hz to 50 000 Hz. The procedure for experimental signal correction to eliminate the frequency characteristics of the measuring system is given. The corrected experimental signal shows a good correlation with theoretically calculated PA signal at frequencies below 32 000 Hz. The corrected experimental PA elastic bending signals for cantilevers with different thicknesses are analyzed. The experimental results allow identifying the resonant frequency (the first resonant mode) of the cantilever vibrations. These values are in good agreement with the theoretically computed values. A theoretical model of the optically excited Si cantilever is derived, taking into account plasmaelastic, thermoelastic, and thermodiffusion mechanisms. Dynamic relations for the amplitude and phase of electronic and thermal elastic vibrations in optically excited cantilevers are derived. The theoretical model is compared to the experimental results

Investigation of Micromechanical Structures by Photoacoustic Elastic Bending Method

Photoacoustic (PA) and photothermal (PT) science and technology extensively developed new methods for the investigation of micro (nano)-mechanical structures. PA and PT effects can be important also as driven mechanisms for optically excited micromechanical structures. The photoacoustic elastic bending method (PA-EBM) is based on the optical excitation of the micromechanical structure and detection of the acoustic response (PA signal) with a very sensitive PA detection system. The experimental PA elastic bending signals of the whole micromechanical structure were measured by using a special constructed PA cell (the gas-microphone detection technique with transmission configuration). The PA amplitude and phase spectra were measured, as a function of the modulation frequency in a frequency range from 20 Hz to 20 000 Hz, for different samples (Si chip with square membrane). The electronic and thermal elastic PA effects (electronic deformation and thermoelastic mechanisms of elastic wave generation) in a Si simply supported rectangular plate (3D geometry), photogenerated by a uniform and intensity-modulated optical beam, were studied. The theoretical model for the PA elastic bending frequency distribution by using the Green function method was given. The amplitude and phase PA signals were calculated and analyzed, including the thermalization and surface and volume recombination heat sources. The theoretical results were compared with experimental data