Abstract
We study theoretically and numerically third-harmonic generation (THG) from model geometries (interfaces, slabs, periodic media) illuminated by Bessel beams produced by focusing an annular intensity profile. Bessel beams exhibit a phase and intensity distribution near focus different from Gaussian beams, resulting in distinct THG phase matching properties and coherent scattering directions. Excitation wave vectors are controlled by adjusting the bounding aperture angles of the Bessel beam. In addition to extended depth-of-field imaging, this opens interesting perspectives for coherent nonlinear microscopy, such as extracting sample spatial frequencies in the λ/8 - λ range in the case of organized media.
Highlights
Coherent nonlinear microscopy techniques such as second-harmonic generation (SHG), thirdharmonic generation (THG) or coherent anti-Stokes Raman scattering (CARS) microscopies are receiving considerable attention
We study theoretically and numerically third-harmonic generation (THG) from model geometries illuminated by Bessel beams produced by focusing an annular intensity profile
These different ranges can be linked to the three phase matching situations as discussed in the previous section: in the absence of dispersion, THG scattering mostly occurs along the longitudinal and lateral phase matching directions
Summary
Coherent nonlinear microscopy techniques such as second-harmonic generation (SHG), thirdharmonic generation (THG) or coherent anti-Stokes Raman scattering (CARS) microscopies are receiving considerable attention These imaging modalities are all compatible with twophoton excited fluorescence (2PEF) microscopy and provide complementary information on sample intrinsic nonlinear optical properties with micrometer three-dimensional (3D) resolution [1,2,3,4]. Bessel beams have received significant attention for microscopy applications Their main characteristic for imaging applications is that they provide an extended depth of field without compromising the lateral resolution of the system, which has been explored in linear microscopy [25, 26], as well as in 2PEF microscopy [27,28,29,30]. Apart from the case of imaging axially periodic media, we will consider THG in the forward direction only (|θTHG| < π/2) since backward THG is in most cases orders of magnitude weaker than forward THG because of larger phase mismatch [42]
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