U. Mizrahi

Picoseconds time resolved photoinduced absorption by infrared active vibrations as a probe for charge photogeneration in MEH-PPV/C60 composites

Abstract We have applied a visible pump mid-infrared probe picosecond time resolved technique, in order to study the photogeneration of charges in MEH-PPV/C 60 composites. The photoinduced infrared active vibrations on the polymer chains have been used as a direct measure for the photogenerated charges. We have found that, within our time resolution of ⋍60 ps, polarons are photogenerated on the MEH-PPV chains with a quantum yield of the order of 5%.

Polaron photogeneration probed by picosecond infrared active vibrations in MEH-PPV

We report picosecond time resolved photoinduced absorption from infrared active vibrations in thin films (≃ 0.1 μm thickness) of MEH-PPV. With an overall spectral resolution of 1 meV and temporal resolution of ≃ 4 psec both in the pump and probe channels, we followed the spectral evolution with time using 565 nm pulsed excitation applied at 80 MHz repetition rate with ≃ 2 x 10 13 photons/cm 2 per pulse. Under these experimental conditions, we found evidence for photogenerated polarons at times <4 psec. The origin of these polarons is briefly discussed.

Dynamics of carriers in resonantly excited quantum-well lasers studied by intersubband absorption

Using infrared picosecond pulses to probe the intersubband absorption of GaAs/AlGaAs quantum-well lasers following their optical excitation, we directly measure the dynamics of carriers in these devices. We find no evidence for excitonic gain even at cryogenic temperatures and resonant excitonic excitation.

Time-resolved spectroscopy of infrared active vibrations in 2,5-dioctyloxy poly(phenylene vinylene) films

Abstract We report on picosecond time resolved spectroscopy of photogenerated infrared active vibrations in thin films of 2,5-dioctyloxy poly(phenylene vinylene). We excited the films by ≃4xa0ps long pulses of 565xa0nm laser light with 2×1013 photons/cm2 per pulse and repetition rate of 76xa0MHz. We then followed the temporal evolution of the infrared active vibrational (IRAV) spectrum using a subsequent, variably delayed, weak tunable IR probe pulses of similar temporal duration. Under these conditions, we show clear spectroscopic evidence for photogenerated infrared active vibrations at times which are shorter than our temporal resolution (

Time-resolved intersubband optical transitions in resonantly optically pumped semiconductor lasers

Abstract Using picosecond visible-pump mid-infrared-probe technique, we directly measured the photoexcited electron dynamics in the first conduction subband of a GaAs/AlGaAs quantum well laser, below and above its threshold. Our results clearly show that even at low temperatures, under optical excitation into the lowest heavy hole exciton resonance, GaAs/GaAlAs quantum well lasers lase in accordance with the common two-plasma model and not from an excitonic phase.

Polarization correlations between single photons emitted by quantum dots in planar microcavities

We measured the second order correlation function between single photons emitted from optically excited single self‐assembled quantum dots embedded in planar microcavities. We clearly distinguish between radiative recombination processes in the presence of a charge in the dot to recombination in its absence. We observed strong correlations of the linear polarization states of photons emitted by the recombining neutral biexcitons and the polarization states of consecutive recombining neutral excitons.

Intensity and circular polarization correlations of single photons from optically excited semiconductor quantum dots

We measure experimentally and discuss theoretically the intensity temporal correlations between photons from two different spectral lines that an optically excited single, self-assembled semiconductor quantum dot, emits. Surprisingly, consecutive photons are preferably emitted with the same circular polarization.

Non-classical light generated by a quantum dot: multi-color photons with tunable statistics

We report the intensity and polarization correlations of two consecutively emitted photons from an optically excited single semiconductor quantum dot (SCQD). We show that a quantum dot is a source of non-classically correlated photons of various wavelengths, emitted due to the recombination of electron–hole (e–h) pairs from different collective many-carrier quantum states confined in the dot. We show that there are excitation power dependent intensity and polarization correlations among photons emitted at the same (“auto-correlations”), and at different wavelengths (“cross-correlations”). We observed a preferentially co-circularly-polarized cross-correlation at low excitation power, which is tentatively explained in terms of long electronic spin memory.

Tunable statistics of multicolor photons emitted from semiconducting quantum dots

We report the intensity auto- and cross-correlation functions of two consecutively emitted photons from an optically excited single semiconductor quantum dot. We show that a quantum dot is not only a source of non-classically correlated monochromatic photons but is also a source of multicolor photons with excitation power dependent correlation properties. We found that the emitted photon statistics is evolving, as the excitation power is increased, from a sub-Poissonian statistics, where the photons are temporally antibunched, to a super-Poissonian one, where they are temporally bunched.