Design and calibration of an experimental ns-pulsed-laser cavity for aerosol ultrafine particle internal structure, morphology, and size control

Aerosol metal or metal-oxide nanoparticles can be systematically produced in reacting flows including flame spray pyrolysis or plasma reactors. Their physical and chemical properties, critical for nanotechnology development, are influenced by internal structure, morphology, and size distribution. Controlling these properties during synthesis, however, remains challenging. Consequently, previous studies have used tube furnaces to induce aggregate sintering and morphological restructuring. While effective, these methods operate over timescales of minutes to hours and require significant energy input, limiting their suitability for rapid and controllable nanoparticle processing.

Nanosecond laser irradiation offers a fundamentally different pathway for aerosol nanoparticle modification. Laser pulses transfer energy directly to particles with nanosecond temporal resolution, producing rapid heating and cooling rates. Laser-induced incandescence (LII) studies have suggested several laser-driven transformations of soot nanoparticles, including graphitization [1] and annealing [2]. For metal nanoparticles, time-resolved LII measurements [4] suggest that aggregates may undergo sintering during a single laser pulse, altering absorption cross-sections and peak particle temperatures [5]. Aerosol gold nanoparticles have also been shown to experience similar transformations under repeated nanosecond laser irradiation pulses, likely associated with laser-induced sintering [6]. Through single or multiple laser pulses, metal nanoparticles may be modified and in the gas phase. However, the effect of laser fluence, number of pulses, and particle properties such as size and polydispersity remains poorly understood.

To address this gap, we designed and experimentally implemented an aerosol metal and metal-oxide nanoparticle processing cavity integrated with a nanosecond Nd:YAG laser (1064 nm). The design considerations and calibration of the system are presented, including particle penetration efficiency measurements as a function of particle size ranging from 10 nm to 100 nm in mobility diameter.
This provides a controlled platform to investigate the interaction of aerosol nanoparticles with repeated nanosecond laser pulses and quantify changes in aggregate morphology, internal structure, and size distribution.
 
References

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[3] Liu, F., Sipkens, T. A., and Corbin, J. C. Applied Physics B 2025, 131, 206.
[4] Sipkens, T.A., Menser, J., Dreier, T. et al. Laser-induced incandescence for non-soot nanoparticles: recent trends and current challenges. Appl. Phys. B 128, 72 (2022). https://doi.org/10.1007/s00340-022-07769-z [GJS1.1][JM1.2]
[5] Robinson-Enebeli, S., Schulz, C., and Daun, K. J. Applied Physics B 2025, 131, 135.
[6] Khabarov, K., Nouraldeen, M., Tikhonov, S., Lizunova, A., Efimov, A., and Ivanov, V. Nanomaterials 2021, 11, 2701.