Who are we? 

The Laser Spectroscopy group is devoted to fundamental studies in the field of (nano)-photonics, applying the results obtained from basic research to the design and demonstration of novel photonic devices with advanced/extended functionalities. The research activity of the group is framed in several disciplines, which includes Optics, Applied Physics and Material Science. 

Currently, the activity of the group is focused on the study of the interaction between metallic nanostructures sustaining localized surface plasmon resonances and nonlinear solid-state lasers to obtain improved operation of the latter systems in the nanoscale with the possibility of self-controlling their spectral and modal properties for a broad range of applications.

The group has a recognized position in the field of optical properties of materials and holds experience in solid-state lasers, optical spectroscopy, nonlinear optics and ferroelectric domain engineering. The group maintains a number of international collaborations and it is regularly funded by competitive research projects. Some examples of their main recent achievements include the demonstration of a plasmon assisted Nd³⁺-based solid-state nanolaser (Nano Letters 16, 895, 2016), or the giant SHG enhancement by two dimensional arrays of hexagonal necklaces prepared on LiNbO₃ ferroelectric crystal (Advanced Materials 2017, in press). It is also worth to mention its active participation in international conferences with 23 invited talks and 16 oral presentations in the last 5 years. The group also holds a recent patent on “Multi-wavelength emitting solid state nanolasers” (Spanish REF. 201631319).

What do we do?

Resarch on multifunctional coherent sources at the nanoscale focusing the attention in three main research lines:

• Control of the optical properties of luminescent ions at the nanoscale
• Development of plasmon assisted solid state nanolasers
• Enhancement of frequency conversion processes at sub-wavelength scales

New optical systems by assembling two dimensional structures on alternate polarity surfaces

We use alternate ferroelectric domain patterns as templates on which plasmonic nanostructures can be assembled. Those elements can be selectively assembled on domain walls or domain surfaces with a specific polarization, in such a way that new 1D and 2D structures, with sizes and geometries defined by the ferroelectric patterning, are going to be obtained onto the configurable patterned polar surfaces.

SEM images of the selectively formed Ag NPs nanostructures formed on the domain boundary surfaces in LiNbO₃ after a photochemical procedure based on ferroelectric lithography.

Spontaneous emission and nonlinear response enhancement by silver nanoparticles in a Nd³⁺-doped periodically poled LiNbO₃ laser crystal

Periodic distributions of silver nanoparticles are self-assembled on a Nd-doped periodicallypoled ferroelectric laser crystal. The plasmonic resonances supported by the metallic arrays produce an enhancement of the Nd³⁺ luminescence, and a remarkable intensification of the second harmonic generated signal. Advanced Materials, 25, 910 (2013).

Plasmon-Assisted Nd³⁺-Based Solid-State Nanolaser

Solid-state lasers constitute essential tools in a variety of scientific and technological areas, being available in many different designs. However, although nanolasing has been successfully achieved for dyes and semiconductor gain media associated with plasmonic structures, the operation of solid-state lasers beyond the diffraction limit has not been reported yet. Here, we demonstrate room temperature laser action with subwavelength confinement in a Nd³⁺-based solid-state laser by means of the localized surface plasmon resonances supported by chains of metallic nanoparticles. We show a 50% reduction of the pump power at threshold and a remarkable 15-fold improvement of the slope efficiency with respect to the bulk laser operation. The results can be extended to the large diversity of solid-state lasers with the subsequent impact on their applications. Nano Letters, 16, 895 (2016).

Selective Plasmon Enhancement of the 1.08 μm Nd³⁺ Laser Stark Transition by Tailoring Ag Nanoparticles Chains on a PPLN Y-cut

Selective photoluminescence enhancement of the specific Nd³⁺ Stark transition for which laser gain has been obtained in Nd³⁺/LiNbO₃ is demonstrated by means of plasmonic resonances with the appropriate symmetry configuration. By using the nonpolar Y-cut of a periodically poled LiNbO₃ crystal as platform for photoreduction of metallic nanostructures, periodically distributed chains of Ag nanoparticles oriented parallel to the ferroelectric c-axis are obtained. This alternative metallic nanostructure configuration supports the resonance between the localized surface plasmon and exclusively the π-polarized Stark laser line of Nd³⁺ ions at 1.08 μm, while maintaining the remaining crystal field transitions unchanged. The work provides the experimental proof on how plasmonic-based optical antennas can be used to influence selectively rare earth optical Stark transitions to improve the performance of solid state laser gain media. Nano Letters, 13, 4391 (2013).

2D Arrays of Hexagonal Plasmonic Necklaces for Enhanced Second Harmonic Generation

Hexagonal plasmonic necklaces of silver nanoparticles organized in 2D superlattices on functional ferroelectric templates are fabricated in large-scale spatial regions by using a surfactant-free photo-deposition process. The plasmonic necklaces support broad radiative plasmonic resonances allowing the enhancement of second harmonic generation (SHG) at the ferroelectric domain boundaries. A 400-fold SHG enhancement is achieved at the near-UV spectral region with subsequent interest for technological applications. Advanced Materials, 29, 1605267 (2017).