Graded-index AR surfaces produced by ion implantation on plastic materials

Spiller, Eberhard; Haller, Ivan; Feder, R.; Baglin, J.E.E.; Hammer, W.

doi:10.1364/ao.19.003022

Cited by 35 publications

(13 citation statements)

References 10 publications

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“…However, application of conventional AR coatings usually requires expensive vacuum processes, and recently developed sol-gel-derived AR coatings still require multiple-step processes, including a thermal or chemical curing stage. [144][145][146] For the design and fabrication of multilayer AR coatings, the choice of materials for the high RI layer is very important. Krogman et al first developed a facile procedure for applying antireflective films by spin-coating polymer substrates with metal oxide nanoparticles.…”

Section: Antireflective Coatingsmentioning

confidence: 99%

High refractive index organic–inorganic nanocomposites: design, synthesis and application

2009

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Section: Antireflective Coatingsmentioning

confidence: 99%

High refractive index organic–inorganic nanocomposites: design, synthesis and application

2009

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“…Theoretically these structures are broadband as long as the profile of index is distributed over a sufficiently longer length compared to the maximum emission wavelength [48]. There have been many efforts to achieve an ideal graded index structures experimentally, having various index profiles including Gaussian, Quintic and exponential [49][50][51]. In the following we provide the bestreported techniques for either obtaining a direct gradual change of refractive index or by producing a gradual structural change of the high index material in the direction orthogonal to the interface to effectively suppress the Fresnel reflection.…”

Section: Structures With Gradually Varying Refractive Indexmentioning

confidence: 99%

Efficient luminescence extraction strategies and anti-reflective coatings to enhance optical refrigeration of semiconductors

Nia

Rezaei

Brown

et al. 2016

Journal of Luminescence

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Laser refrigeration of solids has emerged as a viable solution for vibration-free and compact cooling that does not require any moving parts or cryogenic liquid. So far, rare-earth doped glasses are the only bulk materials that have provided efficient laser cooling based on the anti-Stokes process. These materials have low indices of refraction and are suitable for efficient luminescence extraction. However, up until this date, laser cooling of bulk semiconductors has not been achieved. One major challenge that needs to be addressed is the photoluminescence trapping and the consequent photon recycling. In this paper, we explain various methods to enhance light extraction for the purpose of laser cooling. We specifically provide guidelines for design and fabrication of graded index and subwavelength structures to maximize the extraction efficiency. Furthermore we present novel techniques for increasing the external quantum efficiency and enhancing the overall laser cooling efficiency. * . These include Coulomb assisted laser cooling in piezoelectric materials[8], luminescence-up conversion (known as anti-Stokes optical refrigeration[9]) , frequency down-conversion[10] and superradiance[11] to name a few. However, anti-Stokes has been the dominant mechanism used for laser cooling of condensed matter [9,[12][13][14][15][16][17][18] .Although anti-Stokes optical refrigeration is the subject of this study, efficient luminescence extraction is required to increase the cooling efficiency of all of the aforementioned laser cooling methods. The anti-Stokes mechanism is schematically shown in Fig. 1. The laser source, which is tuned slightly below the bandgap, produces electrons at the bottom of conduction band and holes at the top of the valence band. These carriers interact with the phonons and scatter to the empty energy states. After reaching equilibrium, i.e. once they thermalize with the phonons, the average electron energy increases by kT where k is the Boltzmann Constant and T is the temperature. Therefore, at equilibrium the average energy of the emitted photons by radiative recombination is higher than the absorbed laser photons. In this process, if all of the photogenerated carriers undergo radiative recombination and all the luminescence energy transfers out of the material, there will always be a net energy extraction (i.e. net cooling). The energy extraction results in the temperature drop and continues up to point where kT becomes so small that laser cooling power gets balanced by the heating produced due to parasitic absorption of the laser. The first observation of such a phenomenon was not realized experimentally until 1995, in trivalent ytterbium ion doped heavy-metal-fluoride glass [19]. In rare earth ions, the electronic 4f levels are shielded from the surrounding by the filled 5s and 5p shells, leading to suppression of multi-phonon relaxation[20] and a high radiative recombination rate favorable for optical refrigeration. In addition, the refractive index of the host material is close to the refracti...

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“…These coatings with omni-directional and broadband characteristics can potentially satisfy the requirements of many fields, such as solar cells. Many forms of gradient profiles [5][6][7][8][9] have been studied previously. Kuo et al fabricated a seven-layer graded-index coating with quintic profiles.…”

Section: Introductionmentioning

confidence: 99%