Abstract
We present the optical design of a 9.6-mm diameter fiber-coupled probe for combined femtosecond laser microsurgery and nonlinear optical imaging. Towards enabling clinical use, we successfully reduced the dimensions of our earlier 18-mm microsurgery probe by half, while improving optical performance. We use analytical and computational models to optimize the miniaturized lens system for off-axis scanning aberrations. The optimization reveals that the optical system can be aberration-corrected using simple aspheric relay lenses to achieve diffraction-limited imaging resolution over a large field of view. Before moving forward with custom lenses, we have constructed the 9.6-mm probe using off-the-shelf spherical relay lenses and a 0.55 NA aspheric objective lens. In addition to reducing the diameter by nearly 50% and the total volume by 5 times, we also demonstrate improved lateral and axial resolutions of 1.27 µm and 13.5 µm, respectively, compared to 1.64 µm and 16.4 µm in our previous work. Using this probe, we can successfully image various tissue samples, such as rat tail tendon that required 2-3 × lower laser power than the current state-of-the-art. With further development, image-guided, femtosecond laser microsurgical probes such as this one can enable physicians to achieve the highest level of surgical precision anywhere inside the body.
Highlights
Ablation with femtosecond laser pulses provides unrivaled microsurgical precision in bulk scattering tissue, with minimal thermal or mechanical side effects [1]
When optimizing the optical system using commercially-available relay lenses, it was not feasible to achieve optimized objective lens designs that maintained diffraction-limited focusing over the entire field of view (FOV) while maintaining surfaces that were practical for manufacturing
The calculations show that spherical relay lenses can provide diffraction-limited performance at the center of the FOV, with predicted lateral and axial resolutions on-axis of 0.74 μm and 7.4 μm, respectively, inside agar
Summary
Ablation with femtosecond laser pulses provides unrivaled microsurgical precision in bulk scattering tissue, with minimal thermal or mechanical side effects [1]. Many other clinical applications have been identified in fields such as dentistry [3,4], otology [5,6,7], and laryngology [8,9], for example Unlike ophthalmic applications, these applications require or would benefit from fiber optic delivery of amplified femtosecond laser pulses to the surgical site through a flexible, miniaturized probe. The lack of fiber delivery and precise guidance present hurdles for developing such applications Towards meeting this need, we have recently developed a fiber-coupled and miniaturized femtosecond laser microsurgery probe [10]. We present the realization of our design in a new 9.6-mm diameter probe using an inexpensive spherical relay lens pair and provide characterization of its performance for nonlinear imaging of various tissue samples
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