We theoretically and experimentally investigate the nonlinear evolution of two optical pulses in a silicon waveguide. We provide an analytic solution for the weak probe wave undergoing non-degenerate two-photon absorption (TPA) from the strong pump. At larger pump intensities, we employ a numerical solution to study the interplay between TPA and photo-generated free carriers. We develop a simple and powerful approach to extract and separate out the distinct loss contributions of TPA and free-carrier absorption from readily available experimental data. Our analysis accounts accurately for experimental results in silicon photonic crystal waveguides.
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http://dx.doi.org/10.1364/OE.23.017101 | DOI Listing |
Biomed Opt Express
September 2024
Department of Eletrical and Computer Engineering, The University of Texas at Austin, 2501 Speedway, Austin, TX 78712, USA.
We present a novel approach for deep vascular imaging in rodent cortex at excitation wavelengths susceptible to water absorption using two-photon microscopy with photons of dissimilar wavelengths. We demonstrate that non-degenerate two-photon excitation (ND-2PE) enables imaging in the water absorption window from 1400-1550 nm using two excitation sources with temporally overlapped pulses at 1300 nm and 1600 nm that straddle the absorption window. We explore the brightness spectra of indocyanine green (ICG) and assess its suitability for imaging in the water absorption window.
View Article and Find Full Text PDFJ Phys Chem A
September 2024
Department of Chemistry, University of Alberta, Edmonton T6G 2G2, Alberta, Canada.
Two-photon absorption (2PA), where a pair of photons are absorbed simultaneously, is recognized as a potent bioimaging technique, which depends on the quantified 2PA probability, defined as cross-section (σ). The absorbed photons either have equivalent (ω = ω) or different frequencies (ω ≠ ω), where the former is degenerate 2PA (D-2PA) and the latter is nondegenerate 2PA (ND-2PA). ND-2PA is of particular interest since it is a promising imaging technology with flexibility of photon frequencies and enhanced cross sections, however, it remains a relatively unexplored area compared to D-2PA.
View Article and Find Full Text PDFbioRxiv
January 2024
Department of Eletrical and Computer Engineering, The University of Texas at Austin, 2501 Speedway, Austin, TX 78712, USA.
We present a novel approach for deep vascular imaging in rodent cortex at excitation wavelengths susceptible to water absorption using two-photon microscopy with photons of dissimilar wavelengths. We demonstrate that non-degenerate two-photon excitation (ND-2PE) enables imaging in the water absorption window from 1400-1550 nm using two synchronized excitation sources at 1300 nm and 1600 nm that straddle the absorption window. We explore the brightness spectra of indocyanine green (ICG) and assess its suitability for imaging in the water absorption window.
View Article and Find Full Text PDFWe demonstrate decoherence-tolerant transmission of a Bell state through a single-mode fiber (SMF) using the photon frequency degree of freedom. To this end, a slightly non-degenerate polarization-entangled singlet, | ⟩=(|HV⟩-|VH⟩)/2, is localized at the SMF as the depolarization channel subject to random noise due to incessant fiber bending. Two-photon beats and quantum state tomography jointly verify the absence of collective decoherence, showing that | ⟩ is the sought-after one-dimensional decoherence-free subspace (DFS) pertaining to SMF.
View Article and Find Full Text PDFPhys Chem Chem Phys
June 2023
Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2G2.
Two-photon absorption (2PA) spectroscopy is a robust bioimaging tool that depends on the determined cross-sections (). The absorption of both photons occurs simultaneously with equivalent (degenerate) or different (non-degenerate) photon energies, D-2PA and ND-2PA, respectively. The former has been investigated experimentally and computationally for many systems, while the latter remains relatively unexplored computationally and limited experimentally.
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