CTS-SGER: Thermo-Mechanical Interactions of Ultrashort Laser Pulses with Subsurface Targets of Tissue Models

摘要：超短激光脉冲与组织模型亚表面靶的热机械相互作用利用脉冲宽度大于~1 ns的激光精确地消融生物组织，同时避免对周围组织造成附带的热损伤，往往是一个相当大的挑战，有时在物理上是不可能的。这是因为光能通过其波长相关的吸收系数耦合到生物组织，并几乎完全转化为热，热以由组织热扩散时间决定的速率扩散到光学限制的体积之外。相反，当激光脉冲比组织的特征扩散时间短得多时，激光与组织的非线性相互作用就会出现，如产生等离子体、冲击波和空化气泡。这些物理现象消耗了很大一部分光能并将其转化为动能，从而实现了更精确的消融，同时减少甚至消除了对周围组织的附带热损害。此外，由于光能与生物组织的耦合不再依赖于激光波长，因此有可能消除不必要的表面加热并将相互作用体积聚焦到深层亚表面目标上。该工作的主要智力优点在于建议使用低能量(MJ)高功率(GW)超短激光脉冲(USLP)来诱导更精确的机械驱动的亚表面组织结构的消融，附带的热损伤最小。这是USLP首次用于组织治疗。其目的是量化激光脉冲持续时间从毫秒到飞秒、重复频率从赫兹到兆赫的重复频率对亚表面组织模型目标产生的热(温度、热通量)和机械(应力、应变)影响的大小。具体地说，我们打算将光消融和损伤程度与各种激光的幅度、脉冲持续时间和重复率联系起来，特别是那些USLP。此外，还将建立一个能准确描述实验证据的热力学数学模型。这项拟议的工作将为目前激光治疗血管病变的创新替代方案奠定基础，也可能是消融小血管和其他组织发色团(如良性和恶性色素病变)的唯一解决方案。关于这项工作的更广泛影响，短期影响包括产生实验方法和更好地了解超激光脉冲与各种组织靶标的相互作用。长期影响包括新技术的发展，在这种技术中，地下结构的精确热机械损害得以实现，而附带的热损害被降至最低。

ABSTRACT: Thermo-mechanical interactions of ultrashort laser pulses with subsurface targets of tissue modelsThe precise ablation of biological tissues using lasers with pulse durations longer than ~ 1 ns, while avoiding collateral thermal damage of the surrounding tissue is often quite a challenge and sometimes physically impossible. This is because the optical energy is coupled to the biological tissue through its wavelength-dependent absorption coefficient and transformed almost entirely into heat, which diffuses beyond the optically confined volume at a rate dictated by the tissue thermal diffusion time. In contrast, when laser pulses are much shorter than the characteristic diffusion time of tissue, non-linear laser-tissue interactions arise, such as the generation of plasma, shockwaves and cavitation bubbles. These physical phenomena consume a large portion of the optical energy and transform it into kinetic energy, allowing a more precise ablation while reducing and even eliminating collateral thermal damage to the surrounding tissue. Furthermore, since the coupling of the optical energy to the biological tissue does no longer depend on laser wavelength, it is possible to eliminate unwanted superficial heating and focus the interaction volume onto deep subsurface targets.The primary intellectual merit of the work lies in the proposed used of low energy (mJ) high power (GW) ultra short laser pulses (USLP) to induce a more precise mechanically-driven ablation of subsurface tissue structures with minimal collateral thermal damage. This is the first such use of USLP for tissue treatment. The objectives are to quantify the magnitude of the thermal (temperatures, heat fluxes) and mechanical (stress, strain) effects on subsurface tissue model targets induced by laser pulse durations ranging from the milli- to the femto-second time scale, with repetition rates between the Hz to the MHz frequency domain. Specifically, we intend to correlate the photoablation and extent of damage with the magnitude, pulse duration and repetition rates of a wide variety of lasers, particularly those of USLP. Furthermore, a thermo-mechanical mathematical model that accurately describes the experimental evidence will be developed. The proposed work will set the foundation for an innovative alternative to current laser therapy of vascular lesions and perhaps the only solution for the ablation of small vasculature and other tissue chromophores, such as benign and malignant pigmented lesions. With respect to the broader impacts of the work, the short-term impacts include the generation of experimental methods and better understanding of the interactions of USLP pulses with various tissue targets. The long-term impacts include the development of new technology where precise thermo-mechanical damage of subsurface structures is achieved while collateral thermal damage is minimized.