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TWO-PHOTON ABSORPTION IN SEMICONDUCTORS

TWO-PHOTON ABSORPTION IN SEMICONDUCTORS. Fabien BOITIER , Antoine GODARD, Emmanuel ROSENCHER Claude FABRE. ONERA Palaiseau Laboratoire Kastler Brossel Paris. Measuring intensity correlations : Hanbury-Brown Twiss experiment. Photon Bunching effect. D 2. E 2. E 2. D 2. D 1. E 1. E 1.

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TWO-PHOTON ABSORPTION IN SEMICONDUCTORS

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  1. TWO-PHOTON ABSORPTION IN SEMICONDUCTORS Fabien BOITIER, Antoine GODARD, Emmanuel ROSENCHER Claude FABRE ONERA Palaiseau Laboratoire Kastler Brossel Paris

  2. Measuring intensity correlations : Hanbury-Brown Twiss experiment Photon Bunching effect

  3. D2 E2 E2 D2 D1 E1 E1 D1 Understanding Photon bunching - simple explanation in terms of fluctuating waves - more difficult to understand in terms of photons as particles 1 for shot noise, even present when the intensity is constant, 1 due to extreme fluctuations of the mean intensity in chaotic light Fano’s explanation in terms of constructive interference between undistinguishable paths

  4. bunching chaotic Coherent (single-mode laser) anti-bunching Non-classical Full quantum treatment given by Glauber 2 1 g(2)<1 : no classical explanation possible g(2)>1 : classical explanation possible… … but full quantum explanation still possible and interesting

  5. Experiments usually done with « pseudothermal » light sources laser Detectors response time limits observation of narrow features in time or broad in frequency

  6. How to study broadband sources with ultra-short correlation times ? Use fast nonlinear effects I. Abram et al 1986, Silberberg et al Use Hong Ou Mandel interferometer parametric fluorescence Lame semi-réfléchissante

  7. CB VB Another possibility : two-photon absorption in semi-conductors transient state - Broadband - No phase matching

  8. Two photon characterization of a GaAs phototube N2 = f(P) b= f(l) Two photon absorption coefficient: b ≈ 10 cm/GW @1.55 µm • Quadratic response between 0.1 and 100 µW Low efficiency: not yet a two-photon counter

  9. Photocount histograms and detection operator 1 « click » What is the two-photon counter observable ? classical approach for perfect quantum efficiency acceptable for photon numbers <3 limited efficiency accounted by attenuator in front exact quantum theory of two photon counter remains to be done

  10. Two-photon absorption Intensity correlation apparatus High pass filter Pulsecounter ASE Resolution < fs : Asph. Lens Time delay 10

  11. Interferometric recorded signal Intensity correlation function obtained by low pass filtering Source: cw ASE @ 1.55µm , 4dBm Detector: Hamamatsu PMT GaAs

  12. TPA measurement of g(2)() (1): laser, amplified spontaneous emission, blackbody Boitier et al., Nature phys. 5, 267(2009) • Summary table of the main properties  Bunching  of unfiltered blackbody!

  13. TPA measurement of g(2)() (2): high gain parametric fluorescence with N. Dubreuil, P. Delaye

  14. Whole pulse two photon interferogram CW source ↔

  15. Second order correlation function g(2)() without dispersion compensation with dispersion compensation far from degeneracy near degeneracy Evidence of an extrabunchingeffect

  16. Photon correlations in parametric fluorescence(1) : full quantum calculation quantum state produced by parametric fluorescence of gain G quantum calculation of g(2)(0) (in the experiment G>106) nothing prevents g(2)(0) to be very large in weak sources with large noise ( value of 28 observed on squeezed vacuum (Ping Koy Lam)

  17. Photon correlations in parametric fluorescence(2) : fluctuating field approach - The signal and idler fields are classical fields taken as a sum of wavepackets with random phases fs and fi. -the classical equations of parametric mixing imply: fs+fi=fpump vacuum fluctuations are needed to trigger the spontaneous parametric fluorescence

  18. Photon correlations in parametric fluorescence(3) : corpuscular approach three kinds of photon coincidences: - accidental - pairs due to the twin photon source - linked to the chaotic distribution of pairs

  19. in a dispersive medium : • Ideal case without dispersion • Increase of chromatic dispersion dispersion compensation needed !

  20. CONCLUSION TPA : efficient technique to measure g(2)(t) down to femtosecond range not yet a two-photon counter : efficiency can be improved no measurement so far in the full quantum regime g(2)(t) <1 in ideal tool for high flux isolated photon sources classical and/or quantum effects ? -many competing physical pictures - even classical pictures have some quantum flavour - quantum approach often provides more physical insight and simple calculations than semi-classical ones

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