Application of flowing thermal lens to flow sensors for microchemical chips

A flowing thermal lens microflow velocimeter, in which a photothermally produced local refractive index change (a thermal lens) was used as a tracer, was developed for microchemical chips made of glass. A laser pulse was focused with a microlens on a liquid flow inside a microchannel, and a thermal lens was produced. The thermal lens drifted downstream and was detected using another beam. The velocity was calculated from the time required for the thermal lens to travel between the two points. The microflow velocimeters enabled non-contact measurement with only slight disturbance to the microfluid possible and were suitable for microchemical systems.