Nondegenerate two- and three-photon nonlinearities in semiconductors

Abstract

Two-photon absorption, 2PA, in semiconductors is enhanced by two orders of magnitude due to intermediate-state resonance enhancement, ISRE, for very nondegenerate (ND) photon energies. Associated with this enhancement in loss is enhancement of the nonlinear refractive index, n2. Even larger enhancement of three-photon absorption is calculated and observed. These large nonlinearities have implications for applications including ND two-photon gain and twophoton semiconductor lasers. Calculations for enhancement of ND-2PA in quantum wells is also presented showing another order of magnitude increase in 2PA. Potential devices include room temperature gated infrared detectors for LIDAR and all-optical switches.

Three-photon absorption spectra and bandgap scaling in direct-gap semiconductors

“…In organic optoelectronics, 3PA can be used as an excitation to observe efficient stimulated emission and frequency upconversion fluorescence emission [2][3][4]. 3PA can contribute to highharmonic generation in semiconductor materials [9,10] or may compete with two-photon lasing in direct gap semiconductors [11,12]. Additionally, 3PA in semiconductor quantum dots and nanocrystals has attracted major interest for applications in bio-labeling and imaging agents due to the possibility of using longer excitation wavelengths to achieve deeper penetration depths for super-resolution imaging [1, [13][14][15].…”

Dispersion of nondegenerate nonlinear refraction in semiconductors

“…For λ a = 600 and 750 nm, with perpendicularly polarized waves, n 2 (ω a ; ω b ) is measured to be 3.7 × and 2.4 × smaller respectively than the values measured with parallel polarizations. Note that the theoretical model assuming a twoparabolic band structure cannot account for this effect [22], but these ratios may be used to compare to the theory considering a more realistic band structure such as Kane's model [42,50].…”

“…, with two photons from the excitation and one from the probe absorbed [50]. Assuming temporally Gaussian pulses following [37,48,50] and analytically solving for E a at the back surface of the sample, we obtain:…”