Updated Nomarski interferometer sets benchmarks for spatial resolution of laser plasmas

In certain circumstances, laser-induced plasmas can lead to unwanted effects in many high-power laser applications, such as laser processing. Plasma generation from lasers has been a stubbornly difficult topic to predict owing to its highly nonlinear nature. New work with Nomarski interferometers looks to boost the spatial resolution in imaging such plasmas.

Researchers have developed a new form of Nomarski interferometer that outperforms in spatial resolution for imaging laser-induced plasmas. Traditional Nomarski interferometry uses a low-separation angle Wollaston prism to split and recombine light by polarization. By swapping out this prism with one with a large separation angle, the device from Kimura et al. achieved agreement with plasma propagation models that was orders of magnitude better than similar devices over a wide range of input energies.

“The most innovative aspect is that using a Wollaston prism with a large separation angle allows high spatial resolution and phase accuracy, without losing the simplicity of the Nomarski interferometer,” said author Kuniaki Konishi. “As a result, we succeeded in constructing [a] compact and alignment-friendly experimental setup while reaching sub-micrometer spatial resolution and quantitative accuracy, which could previously only be realized by more complex digital holographic setups.”

Researchers have long used Nomarski interferometers to study plasma densities in part because they’re simple and robust. The drawback had been that they could not deliver detail on the order of micrometers to capture the intricacies of the plasmas.

The group’s time-resolved interferometer was able to capture plasmas with a resolution of 0.87 micrometers.

The group next hopes to use it to further characterize plasma temperature by incorporating amplitude information into their analyses.

Source: “Sub-micrometer spatial resolution Nomarski interferometer for time-resolved complex-amplitude imaging of femtosecond laser-induced air plasma,” by Wataru Kimura, Shotaro Kawano, Ryohei Yamada, Haruyuki Sakurai, Kuniaki Konishi, Norikatsu Mio, Physics of Plasmas (2025). The article can be accessed at https://doi.org/10.1063/5.0270824 .