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Two-dimensional (2D) diffraction gratings have been developed rapidly in several growing areas of research, but most of them were polarization sensitive with limitations toward practical applications. We report a 2D diffraction grating solution for achieving polarization-independent high efficiency property. The grating was designed and fabricated based on thin-film coatings, orthogonally lithography, and ion-beam etching technology. The measured average (−1, 0) order reflective diffraction efficiency (DE) is 74.8% (p-polarization) and 68.2% (s-polarization) from 770 nm to 790 nm and the lowest difference of DE between two polarizations is 0.593% at 785.5 nm incident wavelength of our sample. [ABSTRACT FROM AUTHOR]

It is well known that the location of guided-mode resonance (GMR) in grating waveguide structures closely tracks the leaky mode dispersion curves. In this paper, taking Bragg reflection due to periodicity and interaction between different modes into account, we first present a schematic diagram of the dispersion relations of leaky modes in multimode grating waveguide structures, both for s-polarized (TE mode) and p-polarized (TM mode) incident waves. Due to the perturbation of the grating layer, the interaction between different resonance modes (transverse standing waves) is inevitable. This transverse interference will result in the non-Bragg nature resonance band gaps in the dispersion curves. Exploiting the characteristics of leaky mode dispersions over the full range of the first Brillouin zone, we hoped we could gain some insight into the relationship among the mode interactions, band gaps, and their benefits to optical elements utilizing the GMR effect in grating waveguide structures. Finally, a specific structure is analyzed. [ABSTRACT FROM AUTHOR]

In this work, gold films on two different types of substrates were fabricated by electron beam (e-beam) evaporation, and the femtosecond laser-induced damage properties were evaluated. The first sample was gold film deposited on fused silica, whereas the second was gold deposited on photoresist. 1-on-1 damage tests were implemented by an 800 ± 30 nm laser with pulse duration of 30 fs. Different damage thresholds and morphologies were obtained for the two samples. The damage threshold of the gold film on fused silica was 0.64 J/cm 2 , with the typical damage morphology of thermal ablation and melting; the damage threshold of the gold film on photoresist was 0.30 J/cm 2 , with the typical damage morphology of blisters or peeling off. In order to better understand the impact of the substrate on the properties of the whole sample, the normalized electric field intensity, temperature, and thermal stress distributions were calculated. The adhesion between the gold film and substrate were measured and the experimental results well agreed with the theoretical analysis. The results indicate that gold films deposited onto grating-structured fused silica will have more powerful laser damage resistance performance. [ABSTRACT FROM AUTHOR]

Laser induced damage of Au-coated gratings (ACG) and metal multilayer dielectric gratings (MMDG) for pulse compression were measured using 800 ± 35 nm femto-laser with pulse width of 30.2 fs. The -1st order diffraction efficiency of the ACG is over 90% in wavelength range from 700 to 1000 nm. The MMDG has a 148 nm bandwidth (750–897 nm) with -1st order diffraction efficiency greater than 90%. The laser damage experiment on grating samples was performed in air for single-shot damage. The single-shot damage threshold of the ACG and MMDG was determined to be 0.32 ± 0.02 J/cm 2 and 0.31 ± 0.02 J/cm 2 , respectively. The damage morphologies of the ACG revealed that the damage was attributed to the pinholes at the base of the grating pillars and the weak adhesion between metal layer and photoresist gratings layer. The damage feature combined with near field distribution of MMDG indicated that the damage was due to the nonlinear ionization process of the valence electrons in HfO 2 film. According to analysis results, the laser damage resistance of the ACG can be enhanced through avoiding the appearance of pinholes and increasing adhesion between metal layer and photoresist layer. And for the MMDG, good performance of HfO 2 film, low near field enhancement and single HfO 2 grating structures may increase its laser damage resistance. [ABSTRACT FROM AUTHOR]

Au-coated gratings (ACGs) for chirped pulse compression were irradiated using 800 ± 35 nm multiple laser pulses with duration of 30 fs. The laser-induced damage threshold (LIDT) of Au-coated gratings decreases from 0.35 J/cm 2 to 0.10 J/cm 2 with the increased pulse shots. The near threshold damage feature of Au-coated gratings at different pulses shows blisters. It is indicated that the gradually increased blister height with increasing multiple pulses on ACGs is caused by the accumulation effect. The damage morphologies combine with simulated results indicate that the damage of the ACGs can be attributed to the pinholes at the base of grating pillars and the separation of gold coating and photoresist gratings caused by the photoresist absorbed the incident laser energy. Therefore, we consider the damage threshold can be enhanced by optimizing coating deposition technology to reduce pinholes density and increase the adhesion between the gold and the photoresist. [ABSTRACT FROM AUTHOR]

We report on a polarization-independent all-dielectric trapezoidal bilayer grating with broadband and high diffraction efficiency. The bilayer trapezoidal grating ridge on a reflector consists of an HfO 2 layer and a SiO 2 layer. The theoretical −1st order efficiencies of the grating are more than 95% with wavelength range from 1010 nm to 1080 nm for both TE and TM polarizations. The fabrication tolerances depending on the HfO 2 and SiO 2 layer grating ridge depths are enough to obtain the designed grating using current craft. The fabricated grating with exceeding 94% efficiency from 1000 nm to 1085 nm measured by a non-polarization laser has been fabricated and applied in a spectral beam combining external cavity to combine eight beams into one beam output with 10.77 kW. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a reflecting polarizing beam splitter (RPBS) with a metal-multilayer dielectric grating (MMDG) structure is designed by using a genetic algorithm and the Fourier mode method. The proposed RPBS grating can be operated at a central wavelength of 1053nm. Moreover, this grating can reflect the transverse electric wave in the -1st order and the transverse magnetic wave in the 0th order. The optimized RPBS grating has high extinction ratios of over 20dB from 1030nm to 1076nm at angles ranging from 48.6° to 55.1°. At 1053nm, the highest efficiency of over 98%, as well as polarization extinction ratios of the 0th order and -1st order at 62.2dB and 48.8dB, respectively, is obtained. The optimized MMDG structure shows acceptable tolerances for grating fabrication. This MMDG may be a potential RPBS candidate for use in different optical systems. [Copyright &y& Elsevier]

Abstract: The transmittance property and the near-field distribution of subwavelength broadband antireflective grating directly patterned into the wide bandgap dielectric material as a function of the surface period and groove depth are performed by a rigorous Fourier modal method. It is found that the transmittivity is insensitive for TE and TM polarization, but the near-field distribution associated with laser damage resistance ability is strongly dependent on polarization state of incident light. What''s more, the femtosecond pulse laser damage threshold of surface structure taking into account local maximum electric field enhancement was calculated numerically using a theoretical ionization mechanism model. The higher threshold on the surface period, pulse duration and incident wavelength for TM polarization than that for TE wave is demonstrated quantitatively. [Copyright &y& Elsevier]

Abstract: The transmission guided-mode resonance filters are implemented by integration of diffraction grating into classical thin films to produce high efficiency in the central wavelength and arbitrarily low sideband response over a quite large spectral range. Transmission guided-mode resonance filters require considerable fewer thin films to acquire narrow line width and high peak transmission in the central wavelength compared with classical multilayer high-reflectance coatings with a stack of quarter-wave thickness. The properties of transmission filters with single/double waveguide grating in the different layers of high refection stacks are compared each other. It is demonstrated that the narrow line width transmission filters can be abstained with only two different materials. [Copyright &y& Elsevier]

Abstract: In this paper, we design resonant reflection grating filters employing the second diffracted orders as the leaky modes, then analyze the bandwidth of the reflection peak and the electric field distributions inside the waveguide under resonance. The numeric calculation confirms that ultra-narrow resonant reflection peaks can be observed in these structures. At the same time, strong electric field enhancement appears under resonance. It provides a new approach to diversify the resonant reflection filters and may open a new way to the realization of ultra-narrow bandwidth filters. [Copyright &y& Elsevier]

Abstract: We present designs of high-efficiency compression grating based on total internal reflection (TIR) for picosecond pulse laser at 1053nm. The setup is devised by directly etching gratings into the bottom side of a prism so that light can successfully enter (or exit) the compression grating. Dependence of the −1 order diffraction efficiencies on the constructive parameters is analyzed for TE- and TM-polarized incident light at Littrow angle by using Fourier modal method in order to obtain optimal grating structure. The electric field enhancement within the high-efficiency TIR gratings is regarded as another criterion to optimize the structure of the TIR gratings. With the criterion of high diffraction efficiency, low electric field enhancement and sufficient manufacturing latitude, TIR compression gratings with optimized constructive parameters are obtained for TE- and TM-polarized incident light, respectively. The grating for TE-polarized light exhibits diffraction efficiencies higher than 0.95 within 23nm bandwidth and relatively low square of electric field enhancement ratio of 5.7. Regardless of the internal electric field enhancement, the grating for TM-polarized light provides diffraction efficiencies higher than 0.95 within 42nm bandwidth. With compact structure, such TIR compression gratings made solely of fused silica should be of great interest for application to chirped pulse amplification (CPA) systems. [Copyright &y& Elsevier]

Abstract: Progress of ultra-short high peak power laser depends significantly on laser-induced damage threshold (LIDT) of diffraction grating used in chirped-pulse amplification system. Laser-induced damage experiment was conducted by the standard one-on-one modes and the damage morphology was detected under scanning electron microscope. LIDT of the samples, which are masked on hafnia and on Chrome, are 3.15 and 4.14J/cm2, respectively. Damage process corresponding to the two kinds of samples is described in detail by analyzing the relative damage morphology. The explanation of the difference between the two kinds of samples is given with the analysis of the pollution, which was introduced during the manufacturing process. [Copyright &y& Elsevier]

Abstract: Used in chirped-pulse amplification system and based on multi-layer thin film stack, pulse compressor gratings (PCG) are etched by ion-beam and holographic techniques. Diffraction efficiency and laser-induced damage threshold rely on the structural parameters of gratings. On the other hand, they depend greatly on the design of multi-layer. A theoretic design is given for dielectric multi-layer, which is exposed at 413.1nm and used at 1053nm. The influences of coating design on optical characters are described in detail. The analysis shows that a coating stack of H3L (H2L)∧9H0.5L2.01H meets the specifications of PCG well. And there is good agreement of transmission between experimental and the theoretic design. [Copyright &y& Elsevier]