<p>As a novel layered noble metal dichalcogenide material, palladium
diselenide (PdSe<sub>2</sub>) has attracted wide interest due to its excellent
optical and electronic properties. In this work, a strong third-order nonlinear optical
response of 2D PdSe<sub>2</sub> films is reported. We conduct both open-aperture
(OA) and closed-aperture (CA) Z-scan measurements with a femtosecond pulsed
laser at 800 nm to investigate the nonlinear absorption and nonlinear
refraction, respectively. In the OA experiment, we observe optical limiting
behaviour originating from large two photo absorption (TPA) in the PdSe<sub>2</sub>
film of <i>β =</i> 3.26 ×10<sup>-8</sup>
m/W. In the CA experiment, we measure a peak-valley response corresponding to a
large and negative Kerr nonlinearity of <i>n</i><sub>2</sub>
= -1.33×10<sup>-15</sup> m<sup>2</sup>/W – two orders of magnitude larger than
bulk silicon. In addition, the variation of <i>n</i><sub>2</sub> as a function
of laser intensity is also characterized, with <i>n</i><sub>2</sub> decreasing in magnitude when increasing incident
laser intensity, becoming saturated at <i>n</i><sub>2</sub>
= -9.96×10<sup>-16</sup> m<sup>2</sup>/W at high intensities. Our results show
that the extraordinary third-order nonlinear optical properties of PdSe<sub>2</sub>
have strong potential for high-performance nonlinear photonic devices.</p>
All-optical light storage in bound states in the continuum and release by demand