Abstract
We present the design, implementation and performance analysis of a compact multi-photon endoscope based on a piezo electric scanning tube. A miniature objective lens with a long working distance and a high numerical aperture (≈ 0.5) is designed to provide a diffraction limited spot size. Furthermore, a 1700 nm wavelength femtosecond fiber laser is used as an excitation source to overcome the scattering of biological tissues and reduce water absorption. Therefore, the novel optical system along with the unique wavelength allows us to increase the imaging depth. We demonstrate that the endoscope is capable of performing third and second harmonic generation (THG/SHG) and three-photon excitation fluorescence (3PEF) imaging over a large field of view (> 400 μm) with high lateral resolution (2.2 μm). The compact and lightweight probe design makes it suitable for minimally-invasive in-vivo imaging as a potential alternative to surgical biopsies.
Highlights
Cancer diagnosis in early stages is critical for determining an effective treatment plan
We demonstrate that the endoscope is capable of performing third and second harmonic generation (THG/SHG) and three-photon excitation fluorescence (3PEF) imaging over a large field of view (> 400 μm) with high lateral resolution (2.2 μm)
Disclosures The authors declare that there are no conflicts of interest related to this article
Summary
Cancer diagnosis in early stages is critical for determining an effective treatment plan. To make a compact and flexible endoscope, we need to miniaturize the scanning mechanism, optical system, signal collection assembly and femtosecond laser. In order to generate nonlinear signal a high intensity excitation is required This is achieved by focusing the femtosecond laser beam coming out of the optical fiber using a compact high numerical aperture (NA) optical system. We present a compact multi-photon endoscope design which employs a customized optics to increase the working distance (> 700 μm in water) as well as FOV (> 400 μm). The 1700 nm laser beam is sent through the core of a double-clad fiber to be focused onto the sample using a customized objective lens (discussed below). We can have shorter laser pulses if we generate the shifted soliton in the double-clad fiber This will require us to increase the input pulse energy. We will discuss the scanning mechanism and optical system design
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