Isotropic diffraction induced by concentration gratings in \alpha-LiO3:Fe

Q. Sun, R.A. Rupp, M. Fally, U. Vietze, F. Laeri

Published in: Opt. Commun., 189, 151-159 (2001)

Iron doped lithium iodate of hexagonal modification is investigated by holographic experiments in a geometry where an electrooptic contribution to the diagonal elements of the dielectric permittivity tensor is forbidden by symmetry. Anisotropic diffraction (electroopticaly allowed) which we expected to observe in that geometry did not occur. Instead, isotropic diffraction (electrooptically forbidden) from light-induced gratings was found. To clarify its origin the properties of these gratings are studied as well as photo-induced transparencyocurring in the ultraviolet. The experiments show that two types of gratings exist, one of them being an absorption grating. The second grating is attributed to originate from concentration changes which arise from the transport of ions triggered by non-uniform illumination.

Nanoporous compound materials for optical applications -- Microlasers and microresonators

F. Laeri, J. U. Nöckel

in Handbook of Advanced Electronic and Photonic Materials and Devices, edited by H. S. Nalwa, Volume 6: Nanostructured Materials (Academic, San Diego, 2001), p. 103--151

Hexagonal Resonators for Molecular Sieve Microlasers

Lhoucine Benmohammadi, Ingo Braun, Franco Laeri, Jens Uwe Nöckel, Günther Schulz-Eckloff, Ferdi Schüth, Uwe Vietze, Özlem Weiss, Dieter Wöhrle

Published in: Opt. and Photonics News, 11(12), 30 (2000)

Hexagonal microlasers based on organic dyes in nanoporous crystals

I. Braun(1), G. Ihlein(2), F. Laeri(3), J. U. Nöckel(4), G. Schulz-Ekloff(1), F. Schüth(2), U. Vietze(3), Özlem Weiß(2), D. Wöhrle(1)
(1): University of Bremen, D-28334 Bremen
(2): Max-Planck-Institut für Kohleforschung, D-45470 Mülheim
(4): Max-Planck-Institut für Physik komplexer Systeme, D-01187 Dresden

Published in: Appl. Phys. B, 70, 335-343 (2000)  (online first),

Molecular sieves, such as nanoporous AlPO$_4$-5, can host a wide variety of laser active dyes. We embedded pyridine 2 molecules as a representative of a commercially available dye which fits into the channel pores of the host matrix. Many efficient dye molecules, such as rhodamines, do not fit into the pores. But modifying the structure of the dyes to appear like the used templates allows to increase the amount of encapsulated dyes. The properties of resulting microlasers depend on size and shape of the microresonators, and we discuss a model for microscopic hexagonal ring resonators. In terms of pump needed to reach lasing threshold molecular sieve microlasers are comparable to VCSELs. For dyes which fit into the pores we observed a partial regeneration of photo-induced damage.

Biomimetic morphogenesis of fluorapatite-gelatin composites: fractal growth, the question of intrinsic electric fields, core/shell assemblies, hollow spheres and reorganization of denatureted collagen

S. Busch(1), H. Dolhaine(2), A. DuChesne(3), S. Heinz(1), O. Hochrein(1), F. Laeri(4),O. Podebrad(3), U. Vietze(4), T. Weiland(3), R. Kniep(1)
(1): Max-Planck-Institut für Chemische Physik fester Stoffe, D-01257 Dresden
(2): Henkel KGaA, D-40191 Düsseldorf
(3): Max-Planck-Institut für Polymerforschung, D-55128 Mainz

Published in: Eur. J. Inorg. Chem., 1643-1653 (1999)

The biomimetic growth of fluorapatite in gelatin matrices at ambient temperature (double-diffusion technique) starts with elongated hexagonal-prismatic seeds followed by self-similar branching (fractal growth) and endsup with anisotropic spherical aggregates. The chemicalsystem Fluorapatite/gelatin is closely related to in vivo conditions for bone or tooth formation and is well suited to a detailed investigation of the formation of an inorganic solid with complex morphology (morphogenesis). The fractal stage of the morphogenesis leads to the formation of closed spheres with diameters of up to 150 um. The self-assembled hierarchical growth thereby shows immediate parallels to the topological bransching criteria of the macromolecular starburst dendrimers. A second growth stage around the closed spheres of the first stage is characterized by the formation of concebtric shells consisting of elongated prismatic fluorapatite units with nearly parallel orientation (maximum diameter of the complete core/shell spheres of 1 mm). The specific structure of the core/shell assembly is similar to the dentin/enamel structure in teeth. Together with the idea of the biological significance of electric fields (pyro-, piezoelectricity) during apatite formation under in vivo or biomimetic conditions the present paper considers the composite caracter of the material and the mechanisms of fractal growth (branching criteria and architecture, the influence of intrinsic electric fields etc.).

Zeolite-dye micro lasers

U. Vietze, O. Krauß, F. Laeri (TUD)
G. Ihlein, F. Schüth (University of Frankfurt)
B. Limburg, M. Abraham (IMM, Mainz)

Published in: Phys. Rev. Lett., Vol. 81, 4628-4631 (1998)

We present a new class of micro lasers based on nanoporous molecular sieve host-guest systems. Organic dye guest molecules of 1-Ethyl-4-(4-(p-Dimethylaminophenyl)-1,3-butadienyl)-pyridinium Perchlorat were inserted into the 0.73~nm wide channel pores of a zeolite AlPO$_4$-5 host. The zeolitic micro crystal compounds where hydrothermally synthesized according to a particular host-guestchemical process. The dye molecules are found not only to be aligned along the host channel axis, but to be oriented as well. Single mode laser emission at 687~nm was obtained from a whispering gallery mode oscillating in a 8~$\mu$m-diameter monolithic micro resonator, in which the field is confined by total internal reflection at the natural hexagonal boundaries inside the zeolitic microcrystals.

Ordered porous materials as media for the organization of matter on the nanoscale

G. Ihlein, B. Junges, U. Junges, F. Schüth (University of Frankfurt)
F. Laeri, U. Vietze (TUD)

Published in: Appl. Organomet. Chem., Vol. 12, 305-314 (1998)

Ordered porous inorganic compounds can now be synthesized with pore sizes between 0.3 nm and several tens of nanometers. The sharp pore size distribution of such materials and the ordered pore arrangement open possibilities for using them to organize matter on the nanometer scale. This overview highlights different aspects of this topic, using four selected examples: the spatial organization of molecules with high molecular hyperpolarizability to create a frequency-doubling element; the encapsulation of a laser dye which results in a new class of solid-state lasers; the encapsulation of small metal clusters in mesoporous ordered oxides; and the encapsulation of semiconductor clusters in such oxides.

Characteristic features of ultraviolet photorefraction in iron-doped alpha-LiIO_3 at low temperatures

Jingjun Xu (Universität Osnabrück),
H. Kabelka, R. A. Rupp (Universität Wien)

Published in: Physical Review B, Vol. 57, pp. 9581--9585 (1998)

The temperature dependence of ultraviolet photorefraction of iron doped alpha-LiO_3 crystals is studied. Within the temperature range of 120-220 K diffraction efficiency and two-wave mixing gain increase dramatically with decreasing temperature and become as high as 36% and 3.1 cm^-1, respectively, below 120 K. The results of holographic recording experiments are compared with measurements of the dieelectric susceptance, electric conductivity, and absorbtion of acoustic waves to establish a relationship between the change in photorefraction and the temperature dependence of the dielectric and ultrasonic behavior. Iron doping of alpha-LiIO_3 enhances the photorefraction considerably.

Laser systems specialized for laser spectroscopy at storage rings

T. Engel(1), M. Würtz(1), S. Borneis(2), St.\ Becker(2), I. Klaft(3), A. Kohl(2), T. Kühl(2), F. Laeri(1), D. Marx(2), K. Meier(1), R.
Neumann(2), F. Schmitt(1), P. Seelig(3), L. Völker(2)

(2): Gesellschaft f\"ur Schwerionenforschung GSI, D-64291 Darmstadt
(3): Universität Mainz, Institut für Physik, D-55099 Mainz

Published in: Hyperfine Interactions, Vol. 108, pp.~251--258 (1997)

Laser spectroscopy at storage rings often suffers from a limited resolution due to Doppler-broadened resonances. Broadening is caused by the velocity spread of the ions stored in the beam. In the following, the present status of our work on laser systems specialized on the specific needs of laser spectroscopy at storage rings is reported.

Two pulsed laser systems were developed. One is a dye laser whose spectral bandwidth can be switched by inserting different Littrow-prisms into the resonator. An increase in bandwidth up to a factor of 45 was achieved. This laser was used for fast qualitative scans and high resolution measurements. The other laser system is a Nd:YAG laser pumped optical parametric oscillator. It is a tunable system covering the spectral range from 410 to 4000 nm. Furthermore, a continuous wave laser with a frequency shifted feedback cavity is described. It shows broadband emission with an adjustable bandwidth of up to 4.5 GHz. This laser can be advantageous for laser cooling of ion beams.

A new detector for laser induced recombination at the ESR

A. Kohl(1), T. Kühl(1), H. Winter(1), C. Bruske(1), A. Dax(1), T. Engel(2), S. Faber(2), M. Gerlach(4), P. Heeg(1), O. Kleppner(1), D. Marx(1), K. Meier(2), F. Schmitt(2), P. Seelig(3), M. Würtz(2)

(1): Gesellschaft für Schwerionenforschung GSI, D-64291 Darmstadt
(3): Universität Mainz, Institut für Physik, D-55099 Mainz,
(4): Johann Wolfgang Goethe-Universität Frankfurt, Institut für Kernphysik, D-60486 Frankfurt am Main

Published in: Hyperfine Interactions, Vol. 108, pp. 319--324 (1997)

For laser induced recombination of heavy ions a new detector was developed that in comparison to a multiwire proportional counter provides better time resolution. It is able to cope with very high rates and gives the possibility for easy online monitoring of the detected beam.

Designing resonators with large mode volume and high mode discrimination

Published in: Optics Letters, Vol. 21, pp. 1324--1326 (1996)

We present a new approach to increase the mode volume of stable resonators based on a simulated annealing optimization algorithm. To a certain extent the method allows to predetermine the stationary field distribution of the oscillating lowest loss mode, and, compared to conventional Hermite-Gaussian modes, to increase its loss discrimination against the remaining ensemble of other modes at the same time. We present results for circular symmetric graded phase mirrors which produce a difference between the diffraction losses of the fundamental mode and the other evaluated higher modes of 30%.

Dielectric Investigation of alpha-LiIO

L. G. Jacobson(1), P. Lunkenheimer(2), F. Laeri, U. Vietze, and A. Loidl(2)
(1): Pontifica Universidade Católica do Rio de Janeiro, Departamento de Cincia dos Materiais e Metalurgia, 22453-900 Rio de Janeiro, R.J., Brazil
(2): Universität Augsburg, Experimentalphysik V, Universitätsstr. 2, D-86135 Augsburg, Germany

Published in: Phys. Stat. Sol. (b), Vol. 198, pp.: 871--880 (1996)

The dieelectric properties of hexagonal lithium iodate (alpha-LiIO_3) single crystals have been studied at frequencies 10^-2 Hz <= nu <= 10^9 Hz and temperatures 100 K <= T <= 500 K. Pure and iron doped crystals were investigated.Below approximately 10 kHz, the electric response of the LiIO_3 crystals is almost entirely dominated by the accumulation of space charges at the electrodes. At least two types of ionic charge carriers seem to contribute to the observed conductivity. In addition, dc measurements revealed that electronic conductivity can not be neglected in (alpha-LiIO_3). At frequencies above some 100 kHz the real part of the conductivity sigma' follows a power law sigma' propto nu^s with relatively small exponents s for both, the doped and the undoped compounds. The temperature dependence of sigma' in this region behaves thermally activated with two energy barriers. The high-frequency limit of the dielectric constant epsilon_infty has been determined. In addition, the data have been evaluated using the modulus formalism.

Spatio-temporal coupling of laser fluctuations --- Observations on a laser with internal frequency conversion

F. G. Laeri, N. Deutsch, G. Angelow, M. Müller, and H. Sakowski(1)
(1): Carl Zeiss, D-73446 Oberkochen, Germany

Published in: Applied Physics B, Vol. 63, pp. 339--347 (1996)

The amplitude of standing wave solid state lasers with frequency conversion inside the resonator can become unstable. We investigated the amplitude fluctuations of an end-pumped Nd:YAG-laser at low pump rates (below 160% threshold pump power) and also above. Detecting the individual mode instabilities separately and comparing them with a theoretical laser model, we can trace the origin of the mechanism leading to observed fluctuations. At certain well defined discrete pump levels above 160% threshold the instabilities disappear. These stable emission states are associated with particular nonconventional mode patterns, some of them exhibiting a helical phase structure. Based on experimental observations and computer simulations of pump induced resonator aberrations we describe a mechanism for the emergence of the peculiar transversal modes and laser fluctuations.

Collinear and noncollinear sum-frequency mixing in beta-BBO for a tunable 195--198 nm all-solid-state laser system

J. Lublinski, M. Müller, F. Laeri, and K. Vogler(1)
(1): Aesculap-Meditec, D-90562 Heroldsberg, Germany

Published in: Applied Physics B, Vol. 61, pp. 529--532 (1995)

We attained tunable UV laser radiation between 195 and 198 nm by sum-frequency-mixing two synchronized flashlamp pumped solid-state Q-switch lasers, a Nd:YAG laser frequency quadrupled to 266 nm and a tunable (730--770 nm) alexandrite laser. UV pulse energies of 0.12 mJ with repetition rates of 10 Hz were attained in collinear, as well as noncollinear sum-frequency interaction in a beta-Barium Borate (BBO) crystal with a conversion efficiency of 2.5%. Theoretical models for the noncollinear phase-matching interaction were investigated at UV wavelengths below 200 nm.

Photorefraction in the ultraviolet: materials and effects

F. G. Laeri, R. Jungen, G. Angelow, U. Vietze, T. Engel, M. Würtz, and D. Hilgenberg

Published in: Applied Physics B, Vol. 61, pp. 351--360 (1995)

Doped as well as nominally pure crystals of lithium niobate (LiNbO_3), L-arginine phosphate (LAP), lithium iodate (LiIO_3), potassium dihydrogen phosphate (KDP), lithium formate (LFM), beta barium borate (BBO), and lithium tetra borate were grown and investigated for photorefractive effects at ultraviolet wavelengths down to 333 nm. In nominally undoped LiNbO_3 crystals strong beam coupling effects were observed. In contrast to the visible we revealed a diffusion dominated charge transport mechanism based on holes, and a low photovoltaic field in the order of 550 V/cm. With such a crystal we investigated the modulation transfer function MTF of a lensless image projection system based on a phase conjugation scheme. A spatial frequency response beyond 2800 line pairs per millimeter was observed. Photorefractive beam coupling was also obtained in LiIO_3. Light induced scattering was detected in iron doped LiIO_3 whereas as-grown LAP-material did not exihbit any observable photorefractive effects. However, 100 kV X-ray irradiation seems to induce material defects which can lead to weak light induced scattering at 351 nm. In all other above mentioned materials, doped as well as undoped, light induced scattering could not be observed. On the other side, this is appreciated in in all the applications where the crystals are used as nonlinear material for optical frequency conversion.

Precision laser spectrocscopy of the ground state hyperfine splitting of hydrogenlike ^209Bi^82+

I. Klaft(1) S. Borneis(2), T. Engel, B. Fricke(3), R. Grieser(1), G. Huber(1), T. Kühl(2), D. Marx(2), R. Neumann(2), S. Schröder(2), P. Seelig(2), and L. Völker
(1): Institut für Physik, Universität Mainz, D-55099 Mainz, Germany
(2): Gesellschaft für Schwerionenforschung GSI, D-64220 Darmstadt, Germany
(3): Institut für Physik, Gesamthochschule Kassel, D-34132-Kassel, Germany

Published in: Phys. Rev. Lett., Vol. 73, pp. 2425--2427 (1994)

The first direct observation of a hyperfine splitting in the optical regime is reported. The wavelength of the M 1 transition between the F = 4 and F = 5 hyperfine levels of the ground state of hydrogenlike ^209Bi^82+ was measured to be lambda_0=243.87(4) nm by detection of laser induced fluorescence at the heavy-ion storage ring ESR at GSI. In addition, the lifetime of the laser excited F = 5 sublevel was determined to be tau_0=0.351(16) ms. The method can be applied to a number of other nuclei and should allow a novel test of QED corrections in the previously unexplored combination of strong magnatic and electric fields in highly charged ions.

Efficient ultraviolet photorefraction in LiNbO

R. Jungen, G. Angelow, F. Laeri, and C. Grabmaier(1)
(1): Siemens AG, Otto-Hahn-Ring 6, D-8000 München 83

Published in: Applied Physics A, Vol. 55, pp. 101--103 (1992)

A nominally undoped LiNbO_3 crystal with a slightly broadened absorption edge is used to study beam coupling effects in the UV at 351 nm. At this wavelength the crystal exhibits a diffusion-dominated charge transport mechanism, which allows steady state beam amplification of up to 700 times, comparable to BaTiO_3 in the visible. The used crystal material was characterized by an absorption coefficient alpha=2.68 cm^-1 at 351 nm and a max. gain coefficient Gamma=13.94 cm^-1. This high gain value in the UV can be attributed to a hole diffusion-dominated charge transport mechanism together with a low bulk photovoltaic effect. We measured photovoltaic fields in the order of 550 V/cm.

Some comments on maximum entropy spectral analysis of time series

Published in: Computers in Physics, Vol. 4, pp. 627--636 (1990)

For spectrum estimation of stationary time series the method of maximum entropy, ME, is compared to the method using fast fourier transforms, FFT. As the maximum entropy method is highly nonlinear such a comparison is done on the basis of a simulation. The ME method is introduced and it is demonstrated that especially for short data sequences the ME method is capable of delivering superior spectral estimates. How the ME method works and why the ME estimation produces such unexpectedly good results is discussed. Further the influence of a digitizing signal acquisition apparatus, of additive white noise and of the initial phase on the variability of the estimated spectra are investigated. Fitting an autoregressive process to the time signal is equivalent to the ME procedure. An autoregressive fit code is presented.

Is a resonator containing a phase conjugate mirror a resonator'' ?

Published in: J. Opt. Soc. Am. B, Vol. 7, pp. 2168--2173 (1990)

Different from conventional resonators which exhibit an Airy's formula like transfer function, a resonator containing a phase conjugate mirror, PCMR, shows a cosine phase dependence. But a cosine phase dependence is the characteristic of two-beam interferometers. Does this mean that a PCMR is a two-beam interference device? We show that in a certain sense this is the case. However for a PCMR this does not necessarily contradict the notion of resonator'', that means multiple-beam interference. Applying the discrete-time technique we demonstrate that a PCMR can be decomposed into a series connection of a feedback loop corresponding to an always tuned resonator and a two-beam interferometer. It is this interferometer causing the cosine phase dependence.

Optical noninvasive and nondestructive sensing of the glass transition temperature of 1m thick polymer films

Dietmar Rüger, Christof Reinhard, Franco Laeri, and Heinz Hilgers(1)
(1) IBM-Germany, P.O. Box 2540, D-6500 Mainz, Germany

Published in: SPIE-Proc., Vol. 1265, pp. 29--34 (1990)

Conditions for the glass transition temperature evaluation of a 1 um thick polymer film on an aluminum substrate using laser induced surface acoustic waves propagating along the aluminum surface have been investigated.

Active coherent optical feedback system with phase-conjugating image amplifier

H. Klumb, A. Herden, T. Kobialka, F. Laeri, T. Tschudi, and J. Albers(1)
(1): Institut für Technische Physik, Universität des Saarlandes, Saarbrücken, Germany

Published in: J. Opt. Soc. Am. B, Vol. 5, pp. 22379--2385, (1988)

We present an image transmitting optical feedback system containing a phase-conjugating mirror (PCM) as an amplifying element. The PCM is based on four-wave mixing in a photorefractive BaTiO3 crystal. The ring structure constitutes a new phase-conjugate resonator configuration with the use of the aberration compensating properties of the phase-conjugating element. Injection of a spatially modulated beam into this active feedback system causes image bearing oscillation. Experimental results concerning image transmission and self oscillation are reported.

Nearly degenerate four-wave mixing in photorefractive crystals, an analytical treatment

J. Goltz, F. Laeri, and T. Tschudi

Published in: Optics Communications, Vol.: 64, 63--66 (1987)

We extend the standard model of four-wave mixing in photorefractive crystals to the case where the Bragg-condition is broken by a slight departure from degeneracy. Our analytical treatment shows that for this conditions an increased phase conjugate reflectivity can be obtained.

Angstrom resolution optical profilometry for microscopic objects

Franco Laeri and Timothy C. Strand(1)
(1): IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120-6099, U.S.A.

Published in: Applied Optics, Vol.: 26, pp. 2245--2249 (1987)

An instrument capable of recording the amplitude and phase of reflected light with a phase resolution of better than lambda/3000 and the lateral resolution of a confocal scanning microscope was built. The instrument is based on a commercial microscope body and uses the regular interference contrast optics. The modifications consisted of adding a coherent (heterodyne) detector and a confocal scanning system. Two-dimensional surface images of amplitude, slope, and profile were taken with a step height resolution of typically 0.5--2Å. The instrument is described, and its characteristics for surface profilometry are discussed.

# Kontakt

Dr. Franco Laeri

Laserphysik
Institut für Angewandte Physik
Fachbereich 05 - Physik