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This study presents the concept of high-damage-threshold chirped mirrors (HDTCMs) for ultrafast high-power laser systems. We describe a novel design method for the fabrication of HDTCMs to simultaneously achieve high reflectivity and high laser-induced damage threshold (LIDT) over a broad bandwidth. In the proposed novel structure, the squared electric field distribution oscillations of the laser pulse stagger each other, leading to a low average squared E-field distribution and effectively enhancing the LIDT. As a proof-of-concept study, an HDTCM is designed based on our simulation. The LIDT of the HDTCM increases by a factor of ~2.3. Moreover, a HDTCM pair is successfully applied in a cross-polarized-wave (XPW) filter, supporting a near Fourier transform limit (FLT) 17.7-fs pulse generation. This concept can be generalized to virtually any optical coating design, thus advancing high damage resistant mirror fabrication to a level well suited to high-power laser applications. [ABSTRACT FROM AUTHOR]

We design and numerically investigate a wide angle and broadband perfect absorber with compact multilayer structures. The proposed structure is composed of three stacks of semiconductor films and one metal layer. The absorber presents a broadband absorption between 450 nm and 700 nm with an average absorption above 99.2%. For oblique incidence, the absorber shows an average absorption about 90% for a wide range of incident angles from 0 to 60 with p polarization and s polarization. The electrical field intensity distributions are also studied to disclose the broadband absorption mechanism. This designed broadband absorber appears to have very promising applications in solar thermal energy harvesting, thermal emitters and detection. [ABSTRACT FROM AUTHOR]

Indium tin oxide (ITO) has important application in photoelectronic and photonic devices, demanding effective approach and appropriate parameters to modulate the ITO properties. The effects of laser annealing at 1064 nm with different pulse width (875 ps, 10 ns, and 300 ns) on optical and nonlinear optical properties of ITO films were investigated. Compared with 875 ps and 10 ns, laser annealing at 300 ns significantly improved the near-infrared transmittance of ITO films. The change arises from the elimination of oxygen vacancies and reduction of tin oxides, resulting in the decrease of carrier concentration. Finite element simulations indicate that laser annealing with pulse width of 875 ps and 10 ns have high instantaneous peak temperatures of 1128.5 K and 783 K, respectively, while the temperature accumulation between pulses is negligible. On the contrary, the laser annealing with a pulse width of 300 nshas lower peak transient temperature of 343 K but high static residence temperature of 973 K. The results reveal that the modification of ITO films depends more on the static average temperature rather than the instantaneous peak temperature. The modulation of carrier dynamics in both amplitude and temporal domain was demonstrated after 300 ns laser annealing, achieving ultrafast transient response approximately 150 fs. This work provides theoretical and experimental basis for us to select suitable laser conditions for directional annealing of ITO film to make it suitable for the applications of broad optical spectrum photovoltaic devices or ultrafast optical exchange for high-speed data processing. • Laser annealing (LA) is shown for three pulse widths at approximately 0.2 J/cm2. • LA at 300 ns significantly improves the near-infrared transparency due to the reduction of carrier absorption. • Tailorable amplitude and time scale of carrier transient response are achieved by LA, with ultrafast response time 150 fs. • The modification of ITO properties depends on the static temperature rather than transient peak temperature. [ABSTRACT FROM AUTHOR]

Different laser damage testing protocols, including 1-on-1, S-on-1, and Raster Scan, were conducted on 532 nm polarizers to evaluate the damage resistance and mechanisms. A comparison of the laser-induced damage thresholds (LIDTs) revealed different damage characteristics and major contributions to film failure for different polarizations. For P polarization, the LIDTs for the three test protocols were nearly the same because of the stabilization of two typical damage morphologies of flat-bottomed pits and mussel damage pits. For S polarization, the LIDTs for multiple pulses were lowest, where absorptive defect-induced damage was revealed. The damage characteristics of 532 nm polarizers and 1064 nm polarizers have been also compared. The mussel damage pits, which are similar to the typical damage morphologies of ultraviolet (UV) laser damage to fused silica, were observed for the first time in coatings of 532 nm polarizers. This suggests that, the polishing-induced subsurface damage of fused silica substrates may tend to be excited by a short-wavelength laser rather than the fundamental wavelength. • The damage resistance and damage characteristics of 532 nm polarizers in different laser damage test protocols, including 1-on-1, S-on-1, and Raster Scan, have been summarized, as a reference for thin-film optics in high-power laser applications. • The damage characteristics of 532 nm polarizers and 1064 nm polarizers were compared. The subsurface damage of fused silica substrates is easily excited by short-wavelength lasers. • Mussel pits, associated with the ultraviolet laser damage of fused silica, were observed in the coatings for the first time. [ABSTRACT FROM AUTHOR]

WO 3 thin films fabricated by glancing angle deposition (GLAD) are proposed as excellent electrochromic coatings with favorable ion diffusion. A ∼ 500-nm film prepared by GLAD had a relatively large transmittance modulation. The crystallization structure, surface morphology, chemical state, optical and electrochromic properties of WO 3 thin films were systematically characterized upon annealing treatment. Compared with annealed WO 3 porous nanostructured films, the amorphous as-deposited films exhibited a high coloration efficiency and stable reversibility. Furthermore, the GLAD WO 3 films exhibit the tunable angular selectivity under illumination with p-polarized light because of the birefringence, which could extend the application range of nanostructured films in the electrochromic field. [ABSTRACT FROM AUTHOR]

Damage behavior of HfO 2 and SiO 2 films under subpicosecond irradiation is investigated experimentally and theoretically in this work. The typical damage phenomenon is the transition from isolated submicrometer pits to integral ablation at transitive threshold. The experimental damage thresholds for both coatings are consistent with the theoretical calculation. The rate equation considering the feedback effect of electron number density is applied to calculate the deposited energy density, which illustrates the evolution of damage morphology. [ABSTRACT FROM AUTHOR]

The present work reports the nonlinear optical susceptibility of nanocrystalline ZnSe thin films with different thicknesses, measured using third-order harmonic technology at irradiation wavelengths λ of 1200–1900 nm. The results show that the third-order nonlinear susceptibility χ(3) of ZnSe thin films is a function of the pump wavelength and film thickness. The χ(3) values for the thinner 202-nm film generally decreased with the redshift of the wavelength and were approximately 10−20 m2/V2 at λ ≤ 1500 nm and 10−21 m2/V2 at λ > 1500 nm. The χ(3) values for the thicker 1021-nm film did not follow a decreasing trend, but instead exhibited local peaks at 1350, 1500 and 1750 nm, with a maximum value of approximately 2.4 × 10−19 m2/V2 at λ = 1750 nm. Within 1200–1900 nm, the χ(3) of the thicker film was always greater than that of the thinner film. In addition, a weak second-order harmonic at wavelengths within 1100–1300 nm was observed for the 1021 nm ZnSe thin film. The large difference in the nonlinear optical properties between the thinner and thicker film samples is conjectured to be caused by the increased density of geometric defects and the gradual formation of local anisotropy with increasing film thickness. Nonlinear optical coefficient measurements of ZnSe thin films with different thicknesses over a broad spectrum are important for the application of these films in nonlinear thin-film optoelectronic devices. • The third-order nonlinear susceptibility χ(3) of nanocrystalline ZnSe thin film is a function of irradiation wavelength and film thickness. • Within the spectra for 1200–1900 nm, χ(3) of the thinner 202-nm film generally decreased with the redshift of the wavelength. However, χ(3) of the thicker 1021-nm film exhibited local peaks at 1350, 1500 and 1750 nm. • The χ(3) values of the thicker film were generally greater than those of the thinner film. • An unexpected second-order harmonic was generated behind the thicker film at an incident wavelength of 1100–1300 nm. • The trends for increased density of geometric defects and gradual formation of local anisotropy with increasing film thickness were found. [ABSTRACT FROM AUTHOR]

Titanium dioxide (TiO 2 ) nanostructured thin film (TNF), as an important semiconductor exhibiting large surface-to-volume ratio and unique property, has attracted more and more researches. As an important versatile nanofabrication technique, the glancing angle deposition technique (GLAD) is used to fabricate the TNF, frequently. However, little is known about the influence of GLAD on microstructure, crystalline structure, Ti/O chemical state and photoluminescence (PL) properties of TiO 2 thin films. In this paper, pure anatase TNF and traditional TiO 2 thin film (TTF) were deposited by combining GLAD system with the annealing treatment. All of the prepared TNFs keep discrete nanoscale columnar structures characterized by SEM. The evolution of morphology, crystallization structure, Ti/O chemical state and PL properties of TNFs and TTFs under annealing treatment have been investigated in detail. Simultaneously, comparing with TTFs, the influence of GLAD on TNFs material properties has been analyzed further. With the optimum annealing temperature (400 °C), one can obtain fine nanostructures and pure anatase precipitation of TNFs. The GLAD technique can adjust the preferred crystal orientation of TiO 2 thin films, which can be used as a method of material structural design. Both TNFs and TTFs exhibit broad band (380–700 nm) photoluminescence. Nevertheless, the TNFs exhibit much weaker and smoother PL spectra than that of TTFs, due to the large surface-to-volume ratio. The results indicate the potential good catalytic applications of TNFs deposited by GLAD. [ABSTRACT FROM AUTHOR]

Laser coatings designed for space applications not only encounter harsh space environments, but also suffer from laser irradiation. High-energy radiation in space, such as Gamma rays, can cause defects and other damage to materials, which could contribute to laser damage induced by defect absorption. In this work, we studied the optical properties and structural composition of three groups of 1064 nm multilayer antireflection (AR) coatings irradiated by Gamma rays (345 Gy), and the effect of Gamma ray radiation on the laser-induced damage properties of thin films. Experimental results revealed that after exposure to Gamma ray, the absorption and surface roughness of the AR coating increased while the transmittance decreased. X-ray photoelectron spectroscopy (XPS) analysis confirmed that SiO 2 is more fragile under Gamma radiation compared to Ta 2 O 5 and HfO 2. It was also demonstrated that the Gamma ray damage of AR coatings mainly occurred in the SiO 2 layers, and consist of generation of oxygen vacancies and charging defects. The defects generated by Gamma rays increased the absorption of the laser power by the film, hence increasing the probability of laser-induced damage and reducing the laser-induced damage threshold of the film. The coatings prepared by sputtering deposition technique showed lower probability of damage by Gamma ray radiation compared to electron-beam evaporated coatings. • The optical properties and structural composition of the 1064 nm AR coating after Gamma ray irradiation are studied. • The stability of different oxide materials prepared by different processes after Gamma irradiation is compared. • The damage of the film irradiated by Gamma rays under high-energy laser is studied. • This work provides an important reference for the development of space laser coatings. [ABSTRACT FROM AUTHOR]