Pinto Tiago B, Pinto Sara M A, Piedade Ana P, Serpa Carlos
CQC-IMS, Department of Chemistry, University of Coimbra 3004-535 Coimbra Portugal
CEMMPRE, Department of Mechanical Engineering, University of Coimbra 3030-788 Coimbra Portugal.
Nanoscale Adv. 2023 Jul 17;5(16):4191-4202. doi: 10.1039/d3na00451a. eCollection 2023 Aug 8.
Materials that convert the energy of a laser pulse into heat can generate a photoacoustic wave through thermoelastic expansion with characteristics suitable for improved sensing, imaging, or biological membrane permeation. The present work involves the production and characterization of materials composed of an ultrathin layer of titanium dioxide (<5 μm), where a strong absorber molecule capable of very efficiently converting light into heat (5,10,15,20-tetrakis(4-sulfonylphenyl)porphyrin manganese(iii) acetate) is adsorbed. The influence of the thickness of the TiO layer and the duration of the laser pulse on the generation of photoacoustic waves was studied. Strong absorption in a thin layer enables bandwidths of ∼130 MHz at -6 dB with nanosecond pulse laser excitation. Bandwidths of ∼150 MHz at -6 dB were measured with picosecond pulse laser excitation. Absolute pressures reaching 0.9 MPa under very low energy fluences of 10 mJ cm enabled steep stress gradients of 0.19 MPa ns. A wide bandwidth is achieved and upper high-frequency limits of ∼170 MHz (at -6 dB) are reached by combining short laser pulses and ultrathin absorbing layers.
能将激光脉冲能量转化为热量的材料，可通过热弹性膨胀产生光声波，其特性适用于改进传感、成像或生物膜渗透。目前的工作涉及由超薄二氧化钛层（<5μm）组成的材料的制备和表征，其中吸附了一种能够非常有效地将光转化为热量的强吸收分子（5,10,15,20-四（4-磺酰基苯基）卟啉锰（III）乙酸盐）。研究了TiO层厚度和激光脉冲持续时间对光声波产生的影响。在纳秒脉冲激光激发下，薄层中的强吸收可实现-6dB时约130MHz的带宽。在皮秒脉冲激光激发下，测量到-6dB时约150MHz的带宽。在10mJ/cm的极低能量通量下，绝对压力达到0.9MPa，可实现0.19MPa/ns的陡峭应力梯度。通过结合短激光脉冲和超薄吸收层，可实现宽带宽并达到约170MHz（-6dB）的高频上限。
