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Spectral emittance is a key topic in the study of new compositions, depositions, and mechanical machining of materials for solar absorption and for renewable energies in general. The present work reports on the realization and testing of a new experimental facility for the measurement of directional spectral emittance in the range of 2.5–20 μm. Our setup provides emittance spectral information in a completely controlled environment at medium-high temperatures up to 1200 K. We describe the layout and first tests on the device, comparing the results obtained for hafnium carbide and tantalum diboride ultrarefractory ceramic samples to previous quasi-monochromatic measurements carried out in the PROMES-CNRS (PROcedes, Materiaux et Energie Solaire- Centre National de la Recherche Scientifique, France) solar furnace, obtaining a good agreement. Finally, to assess the reliability of the widely used approach of estimating the spectral emittance from room-temperature reflectance spectrum, we compared the calculation in the 2.5–17 μm spectral range to the experimental high-temperature spectral emittance, obtaining that the spectral trend of calculated and measured curves is similar but the calculated emittance underestimates the measured value.

Magnetic nanofluids consisting of goethite nanoparticles in aqueous suspensions have been successfully synthesized using two sodium-free routes. Nanoparticle morphology, nanofluid stability and optical properties have been studied and compared with a goethite nanofluid whose nanoparticles are synthesized with a different protocol using NaOH. The synthesis procedure determines the nanoparticle size and morphology, which, in turn, is connected to optical properties and their sensitivity to external magnetic fields. The highest sensitivity is shown by the sample synthesized with NaOH, which is characterized by the largest nanoparticles (261±5 nm hydrodynamic size) and whose absolute transmittance values increase or decrease by about 11% and 20%, respectively, depending on to the mutual directions of magnetic field and electromagnetic wave polarization/wave vector, for an applied magnetic field of 5.60 mT. Nanoparticles in the fluid are therefore able to discriminate both the absolute value and the direction of the magnetic field and, moreover, being their response non-spectrally flat, specific spectral ranges exist where their response is maximized.

Intralipid 20% was recently suggested as a diffusive reference standard for tissue simulating phantoms. In this work, we extend previously obtained results to other fat emulsions, specifically Intralipid 10%, Intralipid 30%, Lipovenoes 10%, Lipovenoes 10% PhosphoLipid Reduced, Lipovenoes 20%, Lipofundin S 10%, and Lipofundin S 20%. Of particular importance for practical applications, our measurements carried out at a wavelength of 751 nm show the following features. First, these products show high stability and small batch-to-batch variations in their diffusive optical properties, similar to Intralipid 20%. Second, the absorption coefficient of Intralipid, Lipovenoes, and Lipofundin S are very similar and their measured values are within the experimental errors; moreover the reduced scattering coefficient of Intralipid 20%, Lipovenoes 20%, and Lipofundin S 20% are similar and their measured values are within 5%. Third, the reduced scattering coefficient of Intralipid 10% and Intralipid 30% can be scaled from that of Intralipid 20% with an error of 9% and 2%, respectively. A similar scaling property is valid for Lipovenoes and Lipofundin S. We have verified that this scaling property depends on the composition of the fat emulsions: If the ingredients exactly scale with the concentration then the reduced scattering coefficient almost exactly scale as well.

An innovative flooded mask allows seeing both in air and underwater, thus overcoming the drawbacks of commercially available masks. The underwater telescope scheme is applied to a new flooded scuba mask obtaining correct eyesight in both underwater and above-water conditions. Optical design analyses and a test campaign on a sample of free divers have demonstrated that the mask is able to provide a well-corrected vision in both conditions. Three prototypes, with increasing optical performances, have been optically and mechanically optimized and then realized.

The use of solar divergence collimators is the key for reliable optical tests that reproduce the on-field collector operating conditions. Aiming to test small (<80 mm diameter/diagonal) and large concentrators (80-240 mm diameter/diagonal range), the collimator geometry should be evaluated because of some optical errors introduced by the need of bending the optical axis. This paper discusses the optical characteristics of the beams obtained with straight and bent collimators with solar divergence. The collimated beams are examined by ray tracing simulations, studying the aberrations as a function of bend angle, and measured in laboratory. Finally characterisation tests for sunlight concentrators of various shapes, dimensions and collection features are presented describing instrumentation, optical set-up and methodology to determine collection efficiency, image plane analysis and spot size.

The use of solar divergence collimators is the key for reliable optical tests that reproduce the on-field collector operating conditions. Aiming to test small (<80 mm diameter/diagonal) and large concentrators (80-240 mm diameter/diagonal range), the collimator geometry should be evaluated because of some optical errors introduced by the need of bending the optical axis. This paper discusses the optical characteristics of the beams obtained with straight and bent collimators with solar divergence. The collimated beams are examined by ray tracing simulations, studying the aberrations as a function of bend angle, and measured in laboratory. Finally characterisation tests for sunlight concentrators of various shapes, dimensions and collection features are presented describing instrumentation, optical set-up and methodology to determine collection efficiency, image plane analysis and spot size.

Two-dimensional laser-induced periodic surface structures with a deep-subwavelength periodicity (80 nm ≈ λ/10) are obtained for the first time on diamond surfaces. The distinctive surface nanotexturing is achieved by employing a single step technique that relies on irradiation with two temporally delayed and cross-polarized femtosecond-laser pulses (100 fs duration, 800 nm wavelength, 1 kHz repetition rate) generated with a Michelson-like interferometer configuration, followed by chemical etching of surface debris. In this Letter, we demonstrate that, if the delay between two consecutive pulses is ≤2 ps, the 2D periodicity of nanostructures can be tuned by controlling the number of pulses irradiating the surface. Under scanning mode, the method is effective in treating uniformly large areas of diamond, so to induce remarkable antireflection properties able to enhance the absorptance in the visible up to 50 times and to pave the route toward the creation of metasurfaces for future diamond-based optoelectronic devices.

Continuous-wave laser action has been demonstrated in a diode-pumped Yb:KYF4crystal. Crystal growth, spectroscopic measurements, and laser results are presented. A maximum output power of 505 mW, a slope efficiency of 43%, and a continuous wavelength tunability range of 65nm, from 1013 to 1078 nm, have been obtained at room temperature.

Continuous-wave laser action has been demonstrated in a diode-pumped Yb:KYF_4 crystal. Crystal growth, spectroscopic measurements, and laser results are presented. A maximum output power of 505 mW, a slope efficiency of 43%, and a continuous wavelength tunability range of 65nm, from 1013 to 1078 nm, have been obtained at room temperature.

Continuous-wave mode locking (CW-ML) of a diode-pumped Nd3+:BaY2F8 laser is reported for the first time to our knowledge. Pulses as short as 4.8 ps were measured with a total output power of almost equal to 1 W at 1049 nm, corresponding to 3.4 W of absorbed power from the pump diode at 806 nm. A novel technique for passive stabilization of CW-ML has been demonstrated.

Continuous-wave mode locking (CW-ML) of a diode-pumped Nd^3+:BaY_2F_8 laser is reported for the first time to our knowledge. Pulses as short as 4.8 ps were measured with a total output power of ≈1 W at 1049 nm, corresponding to 3.4 W of absorbed power from the pump diode at 806 nm. A novel technique for passive stabilization of CW-ML has been demonstrated.

Continuous-wave laser action at ∼2 µm is demonstrated in a Tm–Ho:KYF_4 single crystal at room temperature. Crystal growth, spectroscopic measurements, and laser results are presented. An output power in excess of 250 mW is obtained with a tuning range of 99 nm, the largest ever published, to our knowledge, for Tm–Ho in any crystalline host.

Continuous-wave laser action at ~2 µm is demonstrated in a Tm-Ho:KYF4 single crystal at room temperature. Crystal growth, spectroscopic measurements, and laser results are presented. An output power in excess of 250 mW is obtained with a tuning range of 99 nm, the largest ever published, to our knowledge, for Tm-Ho in any crystalline host.

Continuous-wave laser action at ~2μm is demonstrated in a Tm–Ho: KYF_4 single crystal at room temperature. Crystal growth, spectroscopic measurements, and laser results are presented. An output power in excess of 250 mW is obtained with a tuning range of 99 nm, the largest ever published, to our knowledge, for Tm–Ho in any crystalline host.

Yb‐doped Scheelite‐like molybdate and tungstate single crystals are promising quantum‐cutting materials. The cooperative downconversion from donor centers to Yb ions occurs in heavily Yb‐doped crystals of this family. This phenomenon can substantially raise the efficiency of crystalline silicon photovoltaic cells. However, the nature of donor centers is still unknown. Herein, several versions of this nature are tested and discussed: Yb3+ion (its high‐energy charge transfer states); Yb2+ion; self‐trapped exciton at molybdate/tungstate complex; color centers based on oxygen vacancies; accidental impurities. To test these assumptions, a series of Scheelite‐like molybdate and tungstate single crystals (CaMoO4, CaWO4, NaLa(MoO4)2, NaGd(MoO4)2, NaGd(WO4)2, and NaY1−xGdx(WO4)2) are grown, both undoped and doped with different Yb‐concentrations. The complex spectroscopic investigations of these crystals are performed. As a result of the studies, three versions, self‐trapped excitons at [MoO4]/[WO4] complexes, color centers at oxygen vacancies, and accidental impurities, coming into the crystals with MoO3, are rejected. The applicability of the other versions should be refined. Yb‐doped Scheelite‐like molybdate and tungstate single crystals are promising quantum‐cutting materials, which can raise the efficiency of silicon photovoltaic cells. However, the nature of donor centers, participating in this quantum cutting, is still unknown. Herein, several versions of this nature are experimentally tested. As a result, three of them are rejected. Applicability of the other versions should be refined.