A nodule dome removal strategy to improve the laser-induced damage threshold of coatings

Various coatings in high-power laser facilities suffer from laser damage due to nodule defects.We propose a nodule dome removal(NDR)strategy to eliminate unwanted localized electric-field(E-field)enhancement caused by nodule defects,thereby improving the laser-induced damage threshold(LIDT)of laser coatings.It is theoretically demonstrated that the proposed NDR strategy can reduce the localized E-field enhancement of nodules in mirror coatings,polarizer coatings and beam splitter coatings.An ultraviolet(UV)mirror coating is experimentally demonstrated using the NDR strategy.The LIDT is improved to about 1.9 and 2.2 times for the UV mirror coating without artificial nodules and the UV mirror coating with artificial nodule seeds with a diameter of 1000 nm,respectively.The NDR strategy,applicable to coatings prepared by different deposition methods,improves the LIDT of laser coating without affecting other properties,such as the spectrum,stress and surface roughness,indicating its broad applicability in high-LIDT laser coatings.

Nanolaminate-based design for UV laser mirror coatings

With ever-increasing laser power,the requirements for ultraviolet(UV)coatings increase continuously.The fundamental challenge for UV laser-resistant mirror coatings is to simultaneously exhibit a high reflectivity with a large bandwidth and high laser resistance.These characteristics are traditionally achieved by the deposition of laser-resistant layers on highly reflective layers.We propose a“reflectivity and laser resistance in one”design by using tunable nanolaminate layers that serve as an effective layer with a high refractive index and a large optical bandgap.An Al_(2)O_(3)-HfO_(2) nanolaminate-based mirror coating for UV laser applications is experimentally demonstrated using ebeam deposition.The bandwidth,over which the reflectance is >99.5%,is more than twice that of a traditional mirror with a comparable overall thickness.The laser-induced damage threshold is increased by a factor of ~1.3 for 7.6 ns pulses at a wavelength of 355 nm.This tunable,nanolaminate-based new design strategy paves the way toward a new generation of UV coatings for high-power laser applications.

Dichroic laser mirrors with mixture layers and sandwich-like-structure interfaces

The requirements for dichroic laser mirrors continue to increase with the development of laser technology. The challenge of a dichroic laser mirror coating is to simultaneously obtain spectral performance with significantly different reflection or transmission properties as well as a high laser-induced damage threshold(LIDT) at two different wavelengths. Traditional dichroic laser mirrors composed of alternating high-and low-refractive-index pure materials often has difficulty achieving excellent spectral performance and high LIDTs at two wavelengths simultaneously. We propose to use a new design with mixture layers and sandwich-like-structure interfaces to meet the challenging requirements. An Al_(2) O_(3)-HfO_(2) mixture-based dichroic laser mirror, which can be used as a harmonic separator in a fusion-class laser or a pump/signal beam separator in a petawatt-class Ti-sapphire laser system, is experimentally demonstrated using e-beam deposition. The mixture-based dichroic mirror coating shows good spectral performance, fine mechanical property, low absorption, and high LIDT. For the s-polarized 7.7 ns pulses at a wavelength of 532 nm and the p-polarized 12 ns pulses at a wavelength of 1064 nm, the LIDTs are almost doubled. The excellent performance of this new design strategy with mixture layers and sandwich-like-structure interfaces suggests its wide applicability in high-performance laser coating.

Luminescence interference-free lifetime nanothermometry pinpoints in vivo temperature

Luminescence nanothermometry makes non-invasive and real-time temperature readings possible in living animals.However,the spectral fluctuation in tissues and fluids,as well as the interaction between fluorophores and environment hinders accuracy of the thermometry.Here,we report a luminescence lifetime-based nanothermometry which specifically addresses this problem.A temporal based calibration(lifetime sensing)in the NIR range,an endogenous thermal response as well as a polymer encapsulation evading environmental factors,altogether help to pinpoint temperature in vivo.Thanks to the highly condensed NdYb ions in a well-protected tiny core-shell nanocrystal(overall 11 nm),a temperature sensitivity about 2.07%K^(-1)(with 5%Yb^(3+)doped nanoparticles)and an accuracy of 0.27 K(with 25%Yb^(3+)doped nanoparticles)in biological fluids are achieved.Hopefully,combining thermally activated energy transfer nanothermometer with anti-interference lifetime thermometry would provide a more accurate temperature measurement for biological and preclinical studies.