Detection of carbon nanoparticles in suspension by a photothermal technique

In this article, a photothermal technique is presented to detect carbon nanoparticles in suspension and to determine their concentration using the photothermal lens effect and the photothermal beam deflection. Both methods are well researched and described in the corresponding literature. The experimental setup consists of an excitation and a probe laser, and optical devices for beam guidance and signal detection. First, an optical setup to generate both effects in a suspension simultaneously is described. To detect the beam deflection and the beam expansion of the probe beam, different optical detectors were applied; moreover, a graphical CMOS-camera-based method was developed. The dependence of the photothermal effect on the absorption of the pump laser beam is discussed, particularly by varying the concentration of carbon nanoparticles in suspension. It is shown that the absorption of the pump beam and thus the photothermal effects can be modified by changing the concentration of carbon nanoparticles. The measurements with this system are showing that, especially with the graphical method, a determination of the concentration in the low ng⋅ml−1 range is possible.