Fraunhofer-Institut für Optronik, Systemtechnik und Bildauswertung IOSB

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  • Publication
    Confocal fluorescence microscopy with high-NA diffractive lens arrays
    ( 2022)
    Li, Zheng
    ;
    Taphanel, Miro
    ;
    Längle, Thomas
    ;
    Beyerer, Jürgen
    Traditionally, there is a trade-off between the numerical aperture and field of view for a microscope objective. Diffractive lens arrays (DLAs) with overlapping apertures are used to overcome such a problem. A spot array with an NA up to 0.83 and a pitch of 75 m is produced by the proposed DLA at a wavelength of 488 nm. By measurement of the fluorescence beads, the DLA-based confocal setup shows the capability of high-resolution measurement over an area of 3mm 3mm with a 2.5 0.07 NA objective. Further, the proposed fluorescence microscope is insensitive to optical aberrations, which has been demonstrated by imaging with a simple doublet lens.
  • Publication
    3.5 W Broadband PM Hybrid Amplifier at 2051 nm with Holmium- and Thulium-Doped Single-Clad Fibers
    ( 2021)
    Tench, Robert E.
    ;
    Amavigan, Alexandre
    ;
    Romano, Clément
    ;
    Traore, Daniya
    ;
    Delavaux, Jean-Marc
    ;
    Robin, Thierry
    ;
    Cadier, Benoît
    ;
    Laurent, Arnaud
    ;
    Crochet, Patrice
    We report the design and performance of a packaged broadband PM hybrid HDFA/TDFA in the 2000-2100 nm band using all-single-clad doped fibers. Internal small signal G = 49.1 dB, small signal NF = 6.5 dB, and P out = 3.54 W are achieved at l s = 2051 nm. The simulated 3 dB output power bandwidth is 98 nm. Comparisons of experimental data and simulations show good agreement. We investigate through simulations an all-Holmium two stage PM optical amplifier design for comparison to the hybrid PM HDFA/TDFA.
  • Publication
    Fraunhofer Institute of Optronics, System Technologies and Image Exploitation: Introduction to the focus issue
    ( 2021)
    Gladysz, S.
    ;
    Beyerer, J.
    ;
    Eichhorn, M.
    This focus issue offers a glimpse into the breadth and depth of research in optics and image processing at the Fraunhofer Institute of Optronics, System Technologies and Image Exploitation (abbreviated Fraunhofer IOSB). The institute belongs to the Fraunhofer Society, which is Europe's largest organization for applied research. The society comprises 72 institutes spread throughout Germany as well as subsidiaries in several European countries, and the USA, UK, Chile and Singapore, each focusing on different fields of applied science. It is named after the Bavarian physicist Joseph von Fraunhofer (1787-1826), the inventor of the spectrometer, optical lens manufacturer and an entrepreneur who exemplified the goals of the society, i.e.: a focus on research excellence, innovation, and commitment to market and customer-oriented research.
  • Publication
    Mid-infrared optical parametric oscillator pumped by a high-pulse-energy, Q-switched Ho3+:YAG laser
    ( 2021)
    Griesbeck, Michael
    ;
    Büker, Hendrik
    ;
    Eitner, Madeleine
    ;
    Goth, Katharina
    ;
    Braesicke, Peter
    ;
    Eichhorn, Marc
    ;
    Kieleck, Christelle
    A high-pulse-energy mid-infrared light source is presented, based on a zinc-germanium-phosphide optical parametric oscillator (ZGP OPO) pumped by an actively Q-switched high-pulse-energy Ho3+:YAG laser. TheHo3+:YAG pump laser source is capable of generating a pulse energy of 15 mJ from a single Ho3+:YAG rod at room temperature at a pulse repetition frequency (PRF) of 700 Hz. A maximum power of 20.1 W at a central wavelength of 2090 nm can be obtained in continuous operation, with a slope efficiency of 45.1%. A good beam quality with an M2 better than 1.3 was achieved in Q-switched operation. The presented laser architecture was used as a suitable pump source for a ZGP-based OPO. Operated at a PRF of 2 kHz and pumped with a pulse energy of 8 mJ, a low conversion threshold of 1.5 W and a maximum total output power of 6.3 W could be obtained in a linear ZGP based OPO. At maximum power, the peak power of the generated mid-infrared radiation exceeded 120 kW, while the beam quality was affected by the strong gain lens building inside the nonlinear material as a consequence of the high-energy pump pulses.
  • Publication
    Impact of threshold assessment methods in laser-induced damage measurements using the examples of CCD, CMOS, and DMD
    ( 2021)
    Schwarz, Bastian
    ;
    Ritt, Gunnar
    ;
    Eberle, Bernd
    Based on our earlier investigations, we continued and intensified our effort on the assessment of laser-induced damage effects in the visible range on a digital micromirror device (DMD) in comparison to different electro-optical imaging sensors such as complementary metal-oxide-semiconductors (CMOS) and charge-coupled devices (CCD). The main two objectives of our current work are: i) to fill the gap for the damage threshold regarding the time scale of picosecond pulses (527 nm) for CCD and CMOS devices and ii) evaluate the performance of a new device, the DMD, with both nanosecond pulses (532 nm) and picosecond pulses (527 nm) and compare the results with those of the CCD/CMOS. In the course of this research, we improved the experimental setup. Furthermore, we characterized the damage caused by laser pulse energies exceeding the laser-induced damage threshold (LIDT). For both the CMOS and CCD cameras, we received damage thresholds of about 10mJ/cm2 (picosecond pulses). For the DMD, we obtained LIDT values of 130mJ/cm2 (nanosecond laser pulses) and 1500mJ/cm2 (picosecond laser pulses). In case of the CMOS devices, we additionally compared the appearance of the damage obtained from the output signal of the camera under test and the microscope images of the surface of the camera. The first visible changes on the surface of the sensor occurred at energy densities that are an order of magnitude higher than the threshold values related to the output signal.
  • Publication
    Laser safety assessments supported by analyses of reflections from metallic targets irradiated by high-power laser light
    ( 2021)
    Henrichsen, Michael
    ;
    Schwarz, Bastian
    ;
    Ritt, Gunnar
    ;
    Azarian, Adrian
    ;
    Eberle, Bernd
    When using kilowatt-class lasers in outdoor environments, ensuring laser safety turns out to be a complex issue due to the large safety areas that must be respected. For the special cases of collimated or focused laser radiation reflected from ideally flat but naturally rough metallic surfaces, the classical laser hazard analysis is deemed insufficient. In order to investigate the corresponding hazard areas for the aforementioned cases, we performed experiments on laser-matter interactions. Using high-power laser radiation, we studied the spatial and temporal reflection characteristics from four different metallic samples. For the evaluation of total reflection characteristics, we performed curve-fitting methods comprising Gaussian-like specular components, diffuse scattering components according to the ABg-scatter model and Lambertian components. For the investigation of occurring caustics, we developed a dedicated model in order to assess the divergence of the contained structures as a function of distance. Our evaluations have shown that the majority of the reflected power is scattered and based on these findings, that resulting nominal optical hazard distance values, even under worst-case assumptions, are significantly smaller than those of the non-reflected laser beam.
  • Publication
    Detecting vibration features from remote objects based on high-speed imagery
    ( 2021)
    Paunescu, Gabriela
    ;
    Lutzmann, Peter
    ;
    Wegner, Daniel
    ;
    Göhler, Benjamin
    Remote detection of vibrational features from an object is important for many short-range civil applications, but it is also of interest for long-range applications in the defense and security areas. The well-established laser Doppler vibrometry technique is widely used as a high-sensitivity, noncontact method. The development of camera technology in recent years made image-based methods reliable passive alternatives for vibration and dynamic measurements. We investigate and discuss the potential of high-speed imaging technique for medium- and long-range vibration detection. The sensitivity and the limitations of the method are experimentally investigated in comparison to the well-established Doppler vibrometry technique. As atmospheric turbulence is expected to become a limiting factor for long-range applications, imaging in the short-wave IR (SWIR) to mid-wave IR (MWIR) rather than in the visual range is advantageous due to the longer wavelength. We present experiments on the vibration detection from SWIR and MWIR image sequences, as well as additional experiments on the extraction of vibration signature under strong local turbulence conditions.
  • Publication
    Nanosecond pulsed single-frequency two-stage holmium-doped fiber MOPA at 2054 nm and 2090 nm
    ( 2021)
    Lorenz, Dominik
    ;
    Romano, Clément
    ;
    Eichhorn, Marc
    ;
    Kieleck, Christelle
    A single-frequency polarization-maintaining holmium-doped fiber master oscillator power amplifier operating at signal wavelengths of 2054 nm and 2090 nm is presented. The two-stage setup delivers up to 240 W peak power and6.7 µJ pulse energy for a pulse width of 30.2 ns at a repetition rate of 100 kHz. The first amplifier stage is designed by simulation, tailored for high gain at the signal wavelength range, favoring amplification at 2090 nm. The design is discussed, and the measured values are compared with the simulation. The second stage is investigated regarding the efficiency for co- and counter-pumping. Stimulated Brillouin scattering was found to be the limiting factor for pulse peak power scaling in the second stage. The measured output pulse shapes are discussed and compared to pulse shapes derived with the Frantz-Nodvik model.
  • Publication
    High-resolution confocal microscopy with low-NA objectives based on diffractive lens arrays
    ( 2021)
    Li, Zheng
    ;
    Taphanel, Miro
    ;
    Längle, Thomas
    ;
    Beyerer, Jürgen
    High resolution and large fields of view are difficult to achieve simultaneously by microscope objectives. In this work, we develop a reflection confocal microscope based on diffractive lens arrays to solve the problem. We demonstrate a prototype that generates a spot array with a numerical aperture of 0.78. Laterally, experiments show a spatial cutoff frequency of 1024 lp/mm by a 0.15 NA objective, and 912 lp/mm by a 0.07 NA objective with a 785 nm diode laser. Axially, an average height of 961 nm with a standard deviation of 49 nm is measured with a 925.5 nm calibrated step height target.
  • Publication
    High pulse energy ZnGeP2 OPO directly pumped by a Q-switched Tm3+-doped single-oscillator fiber laser
    ( 2021)
    Schneider, Julian
    ;
    Forster, Patrick
    ;
    Romano, Clément
    ;
    Eichhorn, Marc
    ;
    Kieleck, Christelle
    A mid-infrared ZnGeP2 optical parametric oscillator pumped by a Tm3+-doped fiber laser is reported, providing pulse energies of 230µJ, pulse widths of 40 ns, and peak powers of ∼6kW with excellent efficiency and beam quality. The pump source is an actively 𝑄-switched single oscillator optimized to generate high pulse energies.