Three-Photon Absorption Spectra and Bandgap Scaling In Direct-Gap Semiconductors

This paper presents three-photon absorption (3PA) measurement results for nine direct-gap semiconductors, including full 3PA spectra for ZnSe, ZnS, and GaAs. These results, along with our theory of 3PA using an eight-band Kane model (four bands with double spin degeneracy), help to explain the significant disagreements between experiments and theory in the literature to date. 3PA in the eight-band model exhibits quantum interference between the various possible pathways that is not observed in previous two-band theories. We present measurements of degenerate 3PA coefficients in InSb, GaAs, CdTe, CdSe, ZnTe, CdS, ZnSe, ZnO, and ZnS. We examine bandgap, Eg, scaling using -band tunneling and perturbation theories that show agreement with the predicted Eg−7 dependence; however, for those semiconductors for which we measured full 3PA spectra, we observe significant discrepancies with both two-band theories. On the other hand, our eight-band model shows excellent agreement with the spectral data. We then use our eight-band theory to predict the 3PA spectra for 15 different semiconductors in their zinc-blende form. These results allow prediction and interpretation of the 3PA coefficients for various narrow to wide bandgap semiconductors

Spectral and temperature dependence of two-photon and free-carrier absorption in InSb

The nonlinear absorption spectrum of InSb was measured using a combination of tunable similar to 160 fs, similar to 10 ps, and similar to 150 ns IR sources along with a cryostat for controlling the sample temperature to vary the band gap energy from 0.17 to 0.23 eV. The measured nonlinear optical properties in InSb are consistent with those predicted by the models which include two-and three-photon absorption (2PA and 3PA), multiphoton generated free-carrier absorption (FCA) and various recombination mechanisms. Temperature-dependent Z-scan and nonlinear transmission measurements yield information on the temperature and spectral dependence of 2PA, FCA, and carrier recombination processes of Shockley-Read-Hall, and Auger mechanisms. We find good agreement between the measured and the modeled nonlinear properties is possible only when the recently predicted temperature dependence of the FCA is considered. The wavelength-and temperature-dependent 2PA and 3PA coefficients in InSb were experimentally obtained. The inferred values of the 2PA and 3PA are consistent with the scaling rules of a simple two-parabolic band model. We further determine recombination rates from nonlinear transmittance of nanosecond pulses of CO2 laser

Femtosecond-To-Nanosecond Nonlinear Spectroscopy Of Polymethine Molecules

The linear and nonlinear optical properties of a series of polymethine molecules are investigated to study the effects of molecular structure and the host environment on overall nonlinear absorption performance. The linear characterization includes measuring the solvatochromic shifts between absorption and fluorescence peaks and studying the excited-state orientational diffusion kinetics. The nonlinear characterization involves measuring the excited-state absorption spectra with a femtosecond white-light-continuum pump-probe technique and performing Z scans and nonlinear transmission measurements from the picosecond to the nanosecond time regimes. The results of these experiments allow us to develop an energy-level structure for the polymethines, which accurately predicts nonlinear absorption properties from the picosecond to the nanosecond time regimes. From this model we are able to identify the key molecular parameters for improved nonlinear absorption. © 2005 Optical Society of America

Large Enhancement Of Two-Photon Absorption In Semiconductors Using Highly Non-Degenerate Photons

We performed frequency non-degenerate pump-probe experiments in several direct-gap semiconductors using femtosecond and picosecond pulses. Tuning the long wavelength photons in the IR region, we observed a 125-fold enhancement of the two-photon absorption coefficient. © 2010 Optical Society of America

Optimization Of The Double Pump-Probe Technique: Decoupling The Triplet Yield And Cross Section

The synthesis, linear photophysical properties, two-photon absorption (2PA), excited-state transient absorption, and gain spectroscopy of a new fluorene derivative tert-butyl 4,4′-(4,4′ (1E,1′E)-2,2′- (9,9-bis(2-(2-ethoxyethoxy)ethyl)-9H-fluorene-2,7-diyl)bis(ethene-2,1-diyl) bis(4,1 phenylene)]dipiperazine-1-carboxylate (1) are reported. The steady-state linear absorption and fluorescence spectra along with excitation anisotropy, fluorescence lifetimes, and photochemical stability of 1 were investigated in a number of organic solvents at room temperature. The 2PA spectra of 1 with a maximum cross section of ∼300 GM were obtained with a 1-kHz femtosecond laser system using open-aperture Z-scan and two-photon-induced fluorescence methods. The transient excited-state absorption (ESA) and gain kinetics of 1 were investigated by a femtosecond pump-probe methodology. Fast relaxation processes (∼1-2 ps) in the gain and ESA spectra of 1 were revealed in ACN solution, attributable to symmetry-breaking effects in the first excited state. Efficient superfluorescence properties of 1 were observed in a nonpolar solvent under femtosecond excitation. One- and two-photon fluorescence microscopy imaging of HCT 116 cells incubated with probe 1 was accomplished, suggesting the potential of this new probe in two-photon fluorescence microscopy bioimaging. © 2012 American Chemical Society

Spectral And Temperature Dependence Of Nonlinear Absorption In Insb

Temperature dependent two-photon and free-carrier absorption spectra of InSb are measured using a tunable picosecond source via temperature controlled Z-scan experiments and show good agreement with theoretical predictions. Three-photon absorption is also observed. © 2009 Optical Society of America

Large Enhancement of Two-Photon Absorption in Semiconductors Using Highly Non-Degenerate Photons

We performed frequency non-degenerate pump-probe experiments in several direct-gap semiconductors using femtosecond and picosecond pulses. Tuning the long wavelength photons in the IR region, we observed a 125-fold enhancement of the two-photon absorption coefficient. © 2010 Optical Society of America

Spectral And Temperature Dependence Of Nonlinear Absorption In Insb

Temperature dependent two-photon and free-carrier absorption spectra of InSb are measured using a tunable picosecond source via temperature controlled Z-scan experiments and show good agreement with theoretical predictions. Three-photon absorption is also observed. © 2009 Optical Society of America

Three-Photon Absorption Of Gaas And Other Semiconductors

A 4-band Kane model gives good agreement for three-photon absorption spectra of GaAs and other semiconductors, showing quantum interference between pathways; however, 2- band scaling rules showing Eg-7 scaling with bandgap give useful estimates. © OSA 2013

Sensitive Mid-Infrared Detection In Wide-Bandgap Semiconductors Using Extreme Non-Degenerate Two-Photon Absorption

Identifying strong and fast nonlinearities for today\u27s photonic applications is an ongoing effort. Materials and devices are typically sought to achieve increasing nonlinear interactions. We report large enhancement of two-photon absorption through intrinsic resonances using extremely non-degenerate photon pairs. We experimentally demonstrate two-photon absorption enhancements by factors of 100-1,000 over degenerate two-photon absorption in direct-bandgap semiconductors. This enables gated detection of sub-bandgap and sub-100 pJ mid-infrared radiation using large-bandgap detectors at room temperature. Detection characteristics are comparable in performance to liquid-nitrogen-cooled HgCdTe (MCT) detectors. The temporal resolution of this gated detection by two-photon absorption is determined by the gating pulse duration. © 2011 Macmillan Publishers Limited. All rights reserved