Single nano-hole as a new effective nonlinear element for third-harmonic generation

Abstract

In this letter, we report on a particularly strong optical nonlinearity at the nanometer scale in aluminum. A strong optical nonlinearity of the third order was demonstrated on a single nanoslit. Single nanoslits of different aspect ratio were excited by a laser pulse (120 fs) at the wavelength 1.5 µm, leading predominantly to third-harmonic generation (THG). It has been shown that strong surface plasmon resonance in a nanoslit allows the realization of an effective nanolocalized source of third-harmonic radiation. We show also that a nanoslit in a metal film has a significant advantage in nonlinear processes over its Babinet complementary nanostructure (nanorod): the effective abstraction of heat in a film with a slit makes it possible to use much higher laser radiation intensities.

Third harmonic generation in the short-wavelength UV range by a single plasmonic nanostructure

“…4, the THG efficiency of the nanoslits formed in a gold nanofilm exceeds by two orders of magnitude the corresponding efficiency of the nanoslits in the aluminium nanofilm. This fact is surprising, because the coefficient c 3 for aluminium at the fundamental frequency (780 nm) is known to be two orders of magnitude larger than the corresponding value for a gold film [42,43]. Therefore, the THG efficiency of the nanostructures formed in an aluminium nanofilm was expected to exceed greatly that of the nanostructures formed in a gold nanofilm.…”

“…However, recent studies showed that the optical nonlinearity of aluminium greatly exceeds that of gold. In particular, it was shown in [42,43] that aluminium susceptibility c 3 at a wavelength of 1550 nm is three orders of magnitude higher than the corresponding value for gold, while at a wavelength of 780 nm the difference is two orders of magnitude [44]. Thus, one would expect aluminium nanostructures to be more efficient (in comparison with gold nanoparticles) THG sources in the UV range.…”

“…However, a nanohole in a metal screen has a number of advantages for applications in nonlinear nanoplasmonics [34,42]. These are, first, a weak background from the excitation radiation, which is significantly attenuated because of the low nanohole transmittance, and, second, the resistance to high-power radiation due to the efficient heat sink in the metal film where the nanohole is formed [42].…”

“Digitally” addressable and localized on a nanometer-sized scale laser light spot

“…The use of SHRs in nonlinear nanoplasmonics is of special interest for the following reasons [1,2]: (i) the nanohole ensures the absence of a background from the excitation radiation, which is strongly weakened by a low transmission of the nanohole; (ii) the metal screen in which SHR is made ensures an efficient heat removal by the metal film, which, in turn, ensures the stability of the nanostructure to high-intensity radiation, making it possible to realize highly efficient nonlinear optical transformations [2]; (iii) at high intensities of the excitation field, an increase in the temperature of nanostructures does not cause a decrease in the Q factor of the plasmon resonance (resistive heating losses), because the metal film of the SHR efficiently removes heat [2]; (iv) the polarizability of a nanorod is higher than for a nanohole [3], therefore, the use of nanorods ensures a high optical nonlinearity of SHR nanostructures.…”

“…Investigations of SHRs were performed using radiation at a wavelength of 1560 nm, since at this wavelength, aluminum is characterized by strong optical nonlinear properties; thus, the optical nonlinearity coefficient (3) of aluminum is approximately 1000 times higher than that of gold [2]. That is because at 1560 nm wavelength of radiation aluminum has stronger metallic properties than gold: refraction index of Al has higher real part and considerably smaller imaginary part compared to Au.…”