“…If we suppose that the hardly probable case of full freezing of the jet in Fig. 5 c will nevertheless takes place, then this will contradict to the experimental observations [ 1,7,9,17,23,24] where never such large ratios of a length of a jet to a bump separation radius r sep have been obtained. Development of the very long jet in the case # 31 presented in Table 1 and in Fig.…”
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AbstractLaser-produced surface nanostructures show considerable promise for many applications while fundamental questions concerning the corresponding mechanisms of structuring are still debated. Here, we present a simple physical model describing those mechanisms happened in a thin metal film on dielectric substrate irradiated by a tightly focused ultrashort laser pulse. The main ingredients included into the model are (i) the film-substrate hydrodynamic interaction, melting and separation of the film from substrate with velocity increasing with increase of absorbed fluence; (ii) the capillary forces decelerating expansion of the expanding flying film; and (iii) rapid freezing into a solid state if the rate of solidification is comparable or larger than hydrodynamic velocities. The developed model and performed simulations explain appearance of microbump inside the focal spot on the film surface. The model follows experimental findings about gradual transformation of the bump from small parabolic to a conical shape and to the bump with a jet on its tip with increasing fluence. Disruption of the bump as a result of thinning down the liquid film to a few interatomic distances or due to mechanical break-off of solid film is described together with the jetting and formation of one or many droplets. Developed theory opens door for optimizing laser parameters for intended nanostructuring in applications.
“…If we suppose that the hardly probable case of full freezing of the jet in Fig. 5 c will nevertheless takes place, then this will contradict to the experimental observations [ 1,7,9,17,23,24] where never such large ratios of a length of a jet to a bump separation radius r sep have been obtained. Development of the very long jet in the case # 31 presented in Table 1 and in Fig.…”
which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
AbstractLaser-produced surface nanostructures show considerable promise for many applications while fundamental questions concerning the corresponding mechanisms of structuring are still debated. Here, we present a simple physical model describing those mechanisms happened in a thin metal film on dielectric substrate irradiated by a tightly focused ultrashort laser pulse. The main ingredients included into the model are (i) the film-substrate hydrodynamic interaction, melting and separation of the film from substrate with velocity increasing with increase of absorbed fluence; (ii) the capillary forces decelerating expansion of the expanding flying film; and (iii) rapid freezing into a solid state if the rate of solidification is comparable or larger than hydrodynamic velocities. The developed model and performed simulations explain appearance of microbump inside the focal spot on the film surface. The model follows experimental findings about gradual transformation of the bump from small parabolic to a conical shape and to the bump with a jet on its tip with increasing fluence. Disruption of the bump as a result of thinning down the liquid film to a few interatomic distances or due to mechanical break-off of solid film is described together with the jetting and formation of one or many droplets. Developed theory opens door for optimizing laser parameters for intended nanostructuring in applications.
“…Compared to our previous SEIRA-studies using the same microhole-array platform, in this work better plasmonic material-clean silver (99.99% purity) versus the gold-palladium alloy (80:20%) [12]-was used in the sensor fabrication. This expectedly provided much higher analytical-455 versus 5 [12]-and physical-76 versus 20 [12]-enhancement factors for this higher figure-of-merit clean metal. Meanwhile, there are additional ways to increase SEIRA(R) sensitivity for the non-polarized IR sources, using this platform-e.g.…”
Section: Discussionmentioning
confidence: 99%
“…Meanwhile, this nonlinear-optical method relying upon nanoscale near-field enhancement of intense electromagnetic (EM) fields of localized plasmons in the UV-near-IR range [5], in general, has its intrinsic drawbacks, such as critical nanocontamination (poisoning) of sensing nanostructured surfaces, luminescence background, degradation of sensing nanoelements under elevated thermal loads in CW laser fields. As a result, alternative sensing principles-surface-enhanced IR absoprtion/reflection (SEIRA/R)-were previously developed [6], invoking nanoscale enhancement of IR-range fields by localized surface plasmons in metallic surface nanoislands and nanoshells [6][7][8][9][10], or their micro-scale enhancement by delocalized surface plasmon-polaritons (SPP) in diverse regular micropatterns [11,12]. These micro-structured sensing platforms provide an opportunity for luminescence background-free, broadband or spectrally selective IR-range sensing of functional groups-fingerprints of explosives, narcotics.…”
Selective IR absorption at 1261 cm −1 enhanced by 455 times, was demonstrated for rhodamine 6G molecules, covering a 2D-photonic crystal, represented by a regular array of 4-micron wide holes in a 30 nm thick silver film on a CaF 2 substrate. The reference absorption lines were taken near 2900 cm −1 , where the IR radiation is freely channeling through the microholes, indicating the reference substrate coverage by the dye molecules for its relative internal calibration. The limit of background-free detection for the analyte was determined at the level ~10 −2 monolayer.
“…If we suppose that the hardly probable case of full freezing of the jet in Fig. 5 c will nevertheless takes place, then this will contradict to the experimental observations [ 1 , 7 , 9 , 17 , 23 , 24 ] where never such large ratios of a length of a jet to a bump separation radius r sep have been obtained. Fig.…”
Section: Resultsmentioning
confidence: 80%
“…Using UV laser pulse (second harmonics of femtosecond laser 785 nm), the lattice spacing between neighboring nanobumps on the thin gold film may be done less than a micrometer (spatial period of a lattice is 760 nm in [ 6 ]); exactly this type of bumps are considered in this paper. These plane two-dimensional “crystals” enhance absorption of light by dye [ 7 ]. This is important for the super sensor technique like the surface-enhanced infrared absorption (SEIRA) solving similar problems as SERS.…”
Laser-produced surface nanostructures show considerable promise for many applications while fundamental questions concerning the corresponding mechanisms of structuring are still debated. Here, we present a simple physical model describing those mechanisms happened in a thin metal film on dielectric substrate irradiated by a tightly focused ultrashort laser pulse. The main ingredients included into the model are (i) the film–substrate hydrodynamic interaction, melting and separation of the film from substrate with velocity increasing with increase of absorbed fluence; (ii) the capillary forces decelerating expansion of the expanding flying film; and (iii) rapid freezing into a solid state if the rate of solidification is comparable or larger than hydrodynamic velocities. The developed model and performed simulations explain appearance of microbump inside the focal spot on the film surface. The model follows experimental findings about gradual transformation of the bump from small parabolic to a conical shape and to the bump with a jet on its tip with increasing fluence. Disruption of the bump as a result of thinning down the liquid film to a few interatomic distances or due to mechanical break-off of solid film is described together with the jetting and formation of one or many droplets. Developed theory opens door for optimizing laser parameters for intended nanostructuring in applications.
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