Real time micro/nano particle detection and tracking with nanosecond resolution

Real-time optical imaging and tracking of particles in a complex environment to understand coordinated events has attracted researchers from various areas such as biomechanics. Here, we report a way for real time detection and tracking of micron size particles in time-space-wavelength mapping technology by using a single detector. Experimentally, we demonstrate real time tracking of micron size glass particles with 50ns temporal resolution and <3μm spatial resolution. Submicron resolution and faster temporal resolution are achievable with further optimization. The proposed technique utilizes the timewavelength technology, which has been proven to be very effective in real time digitization of ultra fast RF signals, and arbitrary waveform generation by random objects. In this work we use a broad band continuum source generated by a 20MHz fiber laser to emit 50nm short pulses at 1550nm. Following a dispersive time wavelength mapping in a chirped fiber grating and space-time-wavelength mapping through a diffraction grating with 600lines/mm, we generate an elliptical beam where each wavelength component corresponds to different time and position in space. Then the generated beam is focused on an image plane by using 20X-40X microscope objectives. The presence of particles on the image plane induces amplitude modulation on each pulse which is captured in real time by a high speed digitizing oscilloscope with 20GS/s sampling rate. The trajectory of the particle is extracted from the dynamic amplitude modulation in a post processing. The same system has also been utilized for imaging of particles by using one dimensional scanning.