Thermoelastic generation of continuous Lamb waves for microfluidic devices

We use the thermoelastic effect as non-contact method to generate Lamb waves for applications in microfluidics. Our system uses a regeneratively amplified ultrafast Ti:Sapphire laser producing 150 fs pulses at a 250 kHz repetition rate. These pulses are focused onto a commercially available 2 μm thick nitrocellulose membrane coated with gold. Strongly chirped Lamb waves are generated using a cylindrical lens to produce a single line focus. We measure extremely slow phase velocities ranging from 80 to 150 m/s within a frequency range from 250 kHz to 2 MHz. Adjusting the spacing of a multiple line source produces CW Lamb waves at frequencies of 250 kHz, 500 kHz, and 750 kHz. These results show that the thermoelastic effect is a promising non-contact method to generate CW Lamb waves for microfluidic devices.