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We experimentally demonstrate that a probe beam at one wavelength, although exhibiting a weak nonlinear response on its own, can be modulated and controlled by a pump beam at another wavelength in plasmonic nanosuspensions, leading to ring-shaped pattern generation. In particular, we show that the probe and pump wavelengths can be interchanged, but the hollow beam patterns appear only in the probe beam, thanks to the gold nanosuspensions that exhibit a strong nonlinear response to pump beam illumination at the plasmonic resonant frequencies. Colloidal suspensions consisting of either gold nanospheres or gold nanorods are employed as nonlinear media, which give rise to refractive index changes and cross-phase modulation between the two beams. We perform a series of experiments to examine the dynamics of hollow beam generation at a fixed probe power as the pump power is varied and find that nonlinear beam shaping has a different power threshold in different nanosuspensions. Our results will enhance the understanding of nonlinear light–matter interactions in plasmonic nanosuspensions, which may be useful for applications in controlling light by light and in optical limiting.
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Influence of thermal diffusion on the spatial resolution of photothermal microscopy
Photothermal microscopy is a powerful method for investigating biological systems and solid state materials. Using a modulated pump to excite the sample, a continuous probe beam monitors the change in the refractive index of the sample due to the modulated heating. These experiments are typically performed at high frequencies to reduce the 1/f noise, achieving a higher signal to noise ratio. In this paper, we explore how the resolution and sensitivity of the photothermal experiments change when the modulation frequency is brought down below 100kHz. In the instance that the pump and probe are cofocused at the sample, the resolution is determined by the size of the pump beam. On the other hand, when a widefield pump is used, significant broadening occurs for frequencies under 20kHz. This broadening is attributed to thermal diffusion. However, the amount of broadening is less than that expected from the thermal diffusion length, which is about 1.7μm at 10kHz for nanoparticles in glycerol. We also explore the situation where the point spread functions of the pump and probe beams are smaller than the particle size as well as how the penetration depth depends on the properties of the pump and probe beams.
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- Award ID(s):
- 1902403
- PAR ID:
- 10359582
- Editor(s):
- Kabashin, Andrei V.; Farsari, Maria; Mahjouri-Samani, Masoud
- Date Published:
- Journal Name:
- Proc. SPIE 11990, Nanoscale and Quantum Materials: From Synthesis and Laser Processing to Applications
- Volume:
- SPIE 11990
- Page Range / eLocation ID:
- 1199007
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1117/12.2607795
