We demonstrate a variable-focus optoacoustic lens (VFOL) by pneumatically controlling a flexible polymer nano-composite membrane, which can produce laser-generated focused ultrasound (LGFU) with a high peak amplitude (>30 MPa) and a tight focal dimension (several hundred μm) over a wide dynamic range of focus variation (>20 mm) together with a long focal length up to 60 mm, each of which is widest and longest among optoacoustic lenses developed so far. Two different designs in lens dimension have been fabricated and characterized: VFOL-L with a 40-mm diameter and VFOL-S with 10 mm. VFOL-L exhibits a wide dynamic range of focal length variation from 38.52 to 60.39 mm with a center frequency near ~ 10 MHz, which is proper for practical long-range applications with several-cm depth. In comparison, VFOL-S covers a focal variation range from 6.75 to 11.1 mm with ~ 14 MHz, producing a relatively higher-pressure amplitude, which allows the inception of acoustic cavitation at an impedance-mismatched boundary. The nano-composite membrane of VFOL is actuated from a planar to deeply curved shape by externally injecting liquid into the VFOL, resulting in a focal gain up to 255 and a positive peak pressure of > 30 MPa in the VFOL-L case. The minimum-geometrical f-number as low as 0.963 is achieved at the shortest focal length (38.52 mm) with 6-dB lateral and axial spot dimensions of 304 μm and 2.86 mm, respectively. We expect that the proposed VFOL-based LGFU with a high peak pressure, a wide dynamic axial range, and a tight focal dimension are suitably applied for depth-dependent characterization of tissues and shockwave treatment, taking advantages of optoacoustic pulses as input with inherent broadband high-frequency characteristics.

我们通过气动控制柔性聚合物纳米复合膜展示了一种可变焦光声透镜 (VFOL)，该膜可以产生具有高峰值振幅 (>30 MPa) 和紧密焦点尺寸 (几个100 μm）在宽动态范围的焦距变化（> 20 mm）以及长达 60 mm 的长焦距，每个焦距都是迄今为止开发的光声透镜中最宽和最长的。已经制造并表征了两种不同的透镜尺寸设计：直径为 40 毫米的 VFOL-L 和直径为 10 毫米的 VFOL-S。VFOL-L 具有从 38.52 到 60.39 mm 的宽动态焦距变化范围，中心频率接近 ~ 10 MHz，适用于具有几厘米深度的实际远程应用。相比之下，VFOL-S 的焦距变化范围为 6。75 到 11.1 mm 和 ~ 14 MHz，产生相对较高的压力振幅，这允许在阻抗不匹配的边界处开始声空化。VFOL 的纳米复合膜通过将液体从外部注入 VFOL 来驱动从平面形状到深弯曲形状，从而在 VFOL-L 情况下产生高达 255 的焦点增益和 > 30 MPa 的正峰值压力。最小几何在最短焦距 (38.52 mm) 下实现了低至 0.963 的f值，横向和轴向光斑尺寸分别为 304 μm 和 2.86 mm。我们期望所提出的基于 VFOL 的 LGFU 具有高峰值压力、宽动态轴向范围和紧密的焦点尺寸，适用于组织的深度相关表征和冲击波治疗，利用光声脉冲作为具有固有宽带的输入高频特性。