Speaker:
Tian Li
Location:
Address:
Mitchell Physics Building
College Station, Texas 77843-4242
Axicons are lenses that feature one conical and one plano surface and are commonly used to create beams with Bessel intensity profiles. These lenses have a variety of applications such as biomedical imaging with optical coherence tomography, optical trapping, and optical drilling. Traditional axicon fabrication techniques include diamond turning or grinding and polishing of glass or epoxy, and two-photon laser writing. However, these methods generally only allow for single-lens fabrication, and the lenses are characterized by surface roughness with lower achievable efficiencies and angles than for refractive components that are fabricated using the same methods. Recently, researchers from France have developed a technique that allows for parallel fabrication capabilities as well as high surface quality of axicons utilizing microblowing. For the OSA News, I will present their recent publication on their method of microfabrication of axicons by glass blowing.
Two-photon excitation microscopy (TPEM) is the most widely used technique for optically imaging tissues at depths up to several cell layers below the surface. However, since two-photon absorption is such a weak effect, and scattering in biological tissues is so strong, TPEM requires excitation with high-power lasers that can damage or disrupt biological function. That's where entangled photons come in [1]. There have been reports of that two-photon absorption in some molecules can be significantly enhanced when the two incident photons are energy-time entangled with one another [2-4]. However, if one takes a close look at those results, one would not be fully convinced they aren't observing some artifacts due to incomplete filtering of pump light or fluorescence in the BBO crystal. And none of the molecules they studied would be particularly useful as fluorescent markers in two-photon microscopy. In this talk I'll talk about our current observation of the squeezed light induced two-photon absorption enhancement from Fluorescein and DCM in DMSO. To the best of our knowledge, this is the first experimental demonstration of an enhanced two-photon absorption from biomarkers using quantum light. Our experiment has paved the way for a two-photon fluorescence microscope using light intensities more suited to sensitive biological samples. Moreover, since in our experiment we use a CW laser instead of a pulsed one, our entangled-photon beams are extremely monochromatic. It therefore further results in a substantial reduction of damaging effects associated with the dispersive broadening of short pulses through optical components in a classical two-photon microscope, and in an improved beam control in the sample as well.
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