Antoncecchi Alessandro, Zhang Hao, Edward Stephen, Verrina Vanessa, Planken Paul C M, Witte Stefan
Opt Express. 2020 Nov 9;28(23):33937-33947. doi: 10.1364/OE.405875.
We present a high-resolution microscope capable of imaging buried structures through optically opaque materials with micrometer transverse resolution and a nanometer-scale depth sensitivity. The ability to image through such materials is made possible by the use of laser ultrasonic techniques, where an ultrafast laser pulse launches acoustic waves inside an opaque layer and subsequent acoustic echoes from buried interfaces are detected optically by a time-delayed probe pulse. We show that the high frequency of the generated ultrasound waves enables imaging with a transverse resolution only limited by the optical detection system. We present the imaging system and signal analysis and demonstrate its imaging capability on complex microstructured objects through 200 nm thick metal layers and gratings through 500 nm thickness. Furthermore, we characterize the obtained imaging performance, achieving a diffraction-limited transverse resolution of 1.2 μm and a depth sensitivity better than 10 nm.
我们展示了一种高分辨率显微镜，它能够通过光学不透明材料对埋藏结构进行成像，具有微米级的横向分辨率和纳米级的深度灵敏度。通过使用激光超声技术，可以实现透过此类材料成像，其中超快激光脉冲在不透明层内激发声波，随后来自埋藏界面的声学回波由延时探测脉冲进行光学检测。我们表明，所产生的超声波的高频使得成像的横向分辨率仅受光学检测系统限制。我们展示了成像系统和信号分析，并通过200纳米厚的金属层以及500纳米厚的光栅，在复杂的微结构物体上展示了其成像能力。此外，我们对所获得的成像性能进行了表征，实现了1.2微米的衍射极限横向分辨率和优于10纳米的深度灵敏度。
