Holographic femtosecond laser processing for biological tissue

飞秒激光加工（FsLP）提供高空间分辨率，并且由于激光脉冲与材料之间的超短相互作用时间而导致对目标的热破坏减少。此外，当飞秒激光脉冲在透明材料中紧密聚焦时，内部形成空隙和折射率变化。为了制造光学器件，需要大量的处理点。因此，处理速度必须足够高以实现期望的吞吐量。我们已经证明了一个全息FLP（H-FsLP）的平行，任意，和可变图案的功能，这是通过使用液晶空间光调制器（LCSLM）显示的计算全息图（CGH）实现的。在这种并行激光加工方法中，衍射峰的均匀性是目前需要解决的关键问题，我们已经展示了具有多相位菲涅耳透镜（MPFL）的H-FsLP，通过调节组成FFL的中心相位和直径，同时考虑LCSLM的性质和照射激光脉冲的空间轮廓，来优化该MPFL。通过优化，光学系统衍射峰的均匀性最大可达95%。为了进一步提高均匀性，采用了一种结合光学估计的优化方法。均匀性提高到最大值98%。提出了一种具有目标跟踪功能的f-FsLP用于生物组织的处理。采用基于平方差和的块匹配方法测量目标的横向运动。表面位置由一个位移传感器检测以测量轴向移动。目标在横向和轴向的最大跟踪速度分别为255 μm/s和125 μm/s。

Femtosecond laser processing (FsLP) provides high spatial resolution and causes reduced thermal destruction to a target as a result of the ultra-short interaction time between the laser pulse and the material. Furthermore, when a femtosecond laser pulse is tightly focused in a transparent material, a void and a refractive index change are formed inside. To fabricate an optical device, a huge number of processing points is required. Therefore, the processing speed must be sufficiently high to enable the desired throughput. We have demonstrated a holographic FLP (H-FsLP) with parallel, arbitrary, and variable patterning features, which were achieved by using a liquid crystal spatial light modulator (LCSLM) displaying a computer-generated hologram (CGH). In such parallel laser processing methods, the uniformity of the diffraction peaks is presently a key issue to be resolved.We have demonstrated the H-FsLP with a multiplexed-phase Fresnel lenses (MPFL), which were optimized by regulating the center phase and the diameter of the constituent PFLs while taking account of the LCSLM properties and the spatial profile of the irradiated laser pulse. By the optimization, the uniformity of the diffraction peaks in optical system was improved to the maximum value of 95%. To realize further improvement of the uniformity, an optimization method with an optical estimation was applied. The uniformity was improved to the maximum value of 98%. A f-FsLP with a target tracking feature was developed for the processing of biological tissues. The block matching method based on a sum-of-squared-difference metric was used to measure the transverse movement of the target. Surface position was detected with an astigmatic sensor to measure the axial movement. The maximum tracking speeds of the target in the transverse and axial directions were 255 μm/s and 125 μm/s, respectively.