On-line thickness monitor of thin film deposition by thermal evaporation is demonstrated using femtosecond pump-probe photoacoustics. A Ti:sapphire femtosecond laser (wavelength 800 nm, pulse width ~110 fs, pulse energy ~1.3 nJ) is split into a pump and a probe beams. The pump beam is used to instantaneously heat the illuminated area of an aluminum thin film during its deposition on a silicon substrate, whereas the probe beam is used to investigate the change in the transient thermoreflectance ΔR/R. The thermal expansion, by the laser heating, creates stress in the aluminum surface region that generates an acoustic wave of ultrasonic frequency. The travel time of the optically-induced acoustic wave normal to the surface of the thin film is measured to evaluate the thickness of the aluminum in the range of ~32 to 388 nm during the film deposition.

使用飞秒泵浦探针光声技术演示了通过热蒸发沉积薄膜的在线厚度监控器。Ti：蓝宝石飞秒激光器（波长800 nm，脉冲宽度〜110 fs，脉冲能量〜1.3 nJ）被分成泵浦和探测光束。泵浦光束用于在铝薄膜沉积到硅基板的过程中瞬间加热铝薄膜的照明区域，而探测光束用于研究瞬态热反射率ΔR/ R的变化。通过激光加热的热膨胀在铝表面区域产生应力，从而产生超声波频率的声波。测量在薄膜沉积过程中垂直于薄膜表面的光致声波的传播时间，以评估铝的厚度在〜32至388 nm范围内。