Abstract:We present the development of a 5 mm, piezo-actuated, ultrafast laser scalpel for fast tissue microsurgery. Delivery of micro-Joules level energies to the tissue was made possible by a large, 31 μm, air-cored inhibited-coupling Kagome fiber. We overcome the fiber's low NA by using lenses made of high refractive index ZnS, which produced an optimal focusing condition with 0.23 NA objective. The optical design achieved a focused laser spot size of 4.5 μm diameter covering a 75 × 75 μm 2 scan area in a miniaturized setting. The probe could deliver the maximum available laser power, achieving an average fluence of 7.8 J/cm 2 on the tissue surface at 62% transmission efficiency. Such fluences could produce uninterrupted, 40 μm deep cuts at translational speeds of up to 5 mm/s along the tissue. We predicted that the best combination of speed and coverage exists at 8 mm/s for our conditions. The onset of nonlinear absorption in ZnS, however, limited the probe's energy delivery capabilities to 1.4 μJ for linear operation at 1.5 picosecond pulse-widths of our fiber laser. Alternatives like broadband CaF 2 crystals should mitigate such nonlinear limiting behavior. Improved opto-mechanical design and appropriate material selection should allow substantially higher fluence delivery and propel such Kagome fiber-based scalpels towards clinical translation.

By mimicking the variable resolution of the human eye, a newly designed foveated endomicroscopic objective shows the potential to improve current endoscopic based techniques of identifying abnormal tissue in the esophagus and colon. The prototype miniature foveated objective is imaged with a confocal microscope to provide large field of view images combined with a high resolution central region to rapidly observe morphological structures associated with cancer development in a mouse model.

A multimodal endomicroscope was developed for cancer detection that combines hyperspectral and confocal imaging through a single foveated objective and a vibrating optical fiber bundle. Standard clinical examination has a limited ability to identify early stage oral cancer. Optical detection methods are typically restricted by either achievable resolution or a small field-of-view. By combining high resolution and widefield spectral imaging into a single probe, a device was developed that provides spectral and spatial information over a 5 mm field to locate suspicious lesions that can then be inspected in high resolution mode. The device was evaluated on ex vivo biopsies of human oral tumors. M. Gillenwater, "Accuracy of in vivo multimodal optical imaging for detection of oral neoplasia," Cancer Prev.

A miniature laser ablation probe relying on an optical fiber to deliver light requires a high coupling efficiency objective with sufficient magnification in order to provide adequate power and field for surgery. A diffraction-limited optical design is presented that utilizes high refractive index zinc sulfide to meet specifications while reducing the miniature objective down to two lenses. The design has a hypercentric conjugate plane on the fiber side and is telecentric on the tissue end. Two versions of the objective were built on a diamond lathe—a traditional cylindrical design and a custom-tapered mount. Both received an antireflective coating. The objectives performed as designed in terms of observable resolution and field of view as measured by imaging a 1951 USAF resolution target. The slanted edge technique was used to find Strehl ratios of 0.75 and 0.78, respectively, indicating nearly diffraction-limited performance. Finally, preliminary ablation experiments indicated threshold fluence of gold film was comparable to similar reported probes.

A prototype miniature objective was designed and fabricated for use in a laser ablation probe utilizing a piezo scanned fiber to rapidly produce a large cutting region, improving functionality and speed for laser ablation surgery.