Polarization modulation thermal lens microscopy for imaging the orientation of non-spherical nanoparticles

In this paper a far field optical technique we call polarization modulation thermal lens microscopy (PM-TLM) is used for imaging the orientation and dichroism of non-spherical nanoparticles. In PM-TLM, the polarization state of a pump beam is periodically modulated which in turn causes morphology related intensity fluctuations in a continuous probe beam, thus allowing high signal to noise ratio detection with using lock-in amplification. Since PM-TLM uses nanoparticle absorption as the contrast mechanism, it may be used to detect and image nanoparticles of far smaller dimensions than can be observed by conventional dark field optical microscopy. The technique, its implementation and experiment results are presented.