FUNFACS Kick-off meeting Nice 1 USTRAT-Exp. FUNFACS T. Ackemann Department of Physics University of Strathclyde Glasgow, Scotland, UK Institut für Angewandte Physik Westfälische Wilhelms-Universität Münster, Germany

FUNFACS2 Experimental activities at Strathclyde  Photonics group 6 permanent academic staff (including me) solid-state laser semiconductor lasers ( m) fiber lasers quantum optics, laser cooling, Bose-Einstein condensation  Semiconductor spectroscopy and devices 4 permanent academic staff semiconductor characterization nitrides II-VI semiconductors  Institute of Photonics 5 researchers high power mode-locking tunable ultra-stable laser spectroscopy biophotonics photonics at the edge of commercialization

FUNFACS3 Facilities of the lab laser sources (shared with other groups): mode-locked TiSa (ps); cw TiSa high-frequency measurements: 20 GHz sampling oscilloscopes 20 GHz electrical spectrum analyzer background of the photonics group/department/Institute of Photonics: operation of high-power lasers, mode-locking, tunable lasers (solid state and semiconductor) semiconductor processing, characterization and mounting SESAMs, heat sinking (diamond heat spreaders)

FUNFACS4 Personal composition group needs to be build up: in „background“ (Münster): one PhD student working on spatio-temporal dynamics of broad-area VCSELs one undergraduate student working on feedback phenomena in VCSELs principal investigator (May) Postdoc: at least one good applicant available (May/June) PhD student: suitable applicants from EU/overseas

FUNFACS5 Latest results coexistence between different states  optical bistability between homogeneous states or  bistability between pattern and homogeneous state prerequisite for cavity solitons  look for bistable nonlinear optical systems

FUNFACS6 Check in small-area devices abrupt turn-on hysteresis indicates subcritical bifurcation and bistability feedback favors stronger polarisation comp.feedback favors weaker polarisation comp. solitary feed- back

FUNFACS7 Theory group of N. A. Loiko (Minsk): spin-flip model + delayed feedback terms single round-trip (Lang-Kobayashi approximation) birefringence and dichroism of solitary laser anisotropic feedback strength in external cavity thermal shift of solitary laser frequency 100 GHz/mA A. Naumenko, N. A. Loiko, M. Sondermann, K. Jentsch, T. A. Abrupt turn-on and hysteresis in a VCSEL with frequency-selective optical feedback submitted to J. Opt. Soc. Am. B K(  ) transfer function of external resonator

FUNFACS8 Results green/black main pol. red/blue weaker pol. feedback favoring weaker pol. mode bistability between lasing states and off-states; abrupt turn-on; small hysteresis stronger pol. feedback influenced essentially solitary laser

FUNFACS9 Interpretation laser originally blue detuned with respect to grating feedback induced red-shift (increase of power, decrease of carriers)  resonance green/black main pol. red/blue weaker pol.

FUNFACS10 Broad-area lasers: Setup external cavity with holografic grating (1800 lines/mm) Littman configuration asymmetric cavity: cylindrical lens necessary for efficient feedback, “beam capture” near field power optical spectrum M. Sondermann, F. Marino, T.A., R. Jäger: NLGW 2004 devices: 150 µm (U Ulm,  2000)

FUNFACS11 Bistability scan current up and down  hysteresis rather large hysteresis loop robust phenomenon  intense spot in inner part of laser localized structure !?

FUNFACS12 Shape and size  width: 9 µm (FWHM)  rotationally symmetric (ellipticity x-y 2%) in spite of anisotropic cavity  indicates intrinsic mechanism of localization

FUNFACS13 Several localized states ? “normal”invers several LS ? independent ? some indication for independence: tendency for two slightly different frequencies different parameters:

FUNFACS14 Switch-on of LS no addressing beamaddressing beam onaddressing beam blocked focus spontaneous emission back in laser

FUNFACS15 Setup: Littrow grating in Littrow configuration beam collimated on grating (2 lenses, exact configuration unclear) laser (U Ulm 2001/2002) „homogeneous“ cavity resonance, „Nature“ laser (150 µm) another 200 µm laser, but with „hole“ in emission pattern large f addressing beam from master laser third experiment (INLN, Dec. 2004) M. Schulz-Ruthenberg, X. Hachair, M. Giudici (+T.A., J. Tredicce)

FUNFACS16 Results for Littrow Tuning of feedback frequency for constant current tendency for bistability, if „stripes“

FUNFACS17 Bistability...but not very stable local detection

FUNFACS18 Results for Littrow Only result, where WB could ignite a stable LS Switching off was not accomplished external laser No writing beamWriting beam ignites LSWriting beam off, LS stays

FUNFACS19 Previous experiment: Littrow second experiment (INLN, summer 2004) X. Hachair Littrow setup addressing beam obtained by reinjecting the output beam (1:1 image) spontaneous appearance of localized spots switch-down possible for certain phases switch-on not achieved, presumingly because spontaneous emission was not focused

FUNFACS20 Status VEGSEL still promising approach  switch-on and off achieved, though in different experiments unclear: no success with 40 µm VCSELs operating at 780 nm optimize  coupling to external cavity, beam parameters, geometry  intra-cavity losses A. Naumenko, N. A. Loiko, M. Sondermann, T. A. PRA (2003) experiment (8µm laser) single-round trip approx. exact (assuming „typical“ VCSEL parameters)

FUNFACS21 Properties of external cavity works only in geometrical optics beam broadening due to diffraction  f 1  focus on mirror L Gaussian beam optics: beam waist on mirror obvious solution: B=C=0 (telescope d 1 = f 1 = d 2 =L/2 ) other solutions with d 1  f 1 (but d 1  f 1 for large L) exist, but not necessarily for a given combination of spot size (respectively z r ), focal length f 1 and cavity length L  cavity design d1d1 d2d2

FUNFACS22 Properties of external cavity II on-axis soliton ok, but off-axis  inversion ff telescope with 1 lens telescope with 2 lenses f 1 + f 2 additional constraint: rays need to be parallel at grating incidence angle different for on-axis and off- axis solitons  different feedback conditions ? 2 lens telescope  column of CS orthogonal to grating plane in laser center (possibly astigmatic telescopes with odd/even number of lenses in orthogonal directions) first experiment:

FUNFACS23 Objectives  WP1, Task 2: VEGSEL (VCSEL with frequency-selective feedback) optimization of cavity design minimization of losses demonstration of up- and down-switching of independent CS focus in first 9 month  WP2, Task 1: 3D light localization in VECSEL with intracavity saturable absorber design of cavity and SESAM test experiments with small-area laser transfer to broad-area technology problem: matching of wavelengths of SESAMs and VCSELs 980/850 nm QD SESAMs ?  WP2, Task 2: 3D light localization in VEGSEL with a long cavity add second cavity ? possibly enhance regularity transiently by perturbation with ps pulse (analogous to synchronous pumping) rather low priority  WP3: only administrative in first 18 month