Grating is a very useful diffraction optical element. Highly efficient and broadband gratings are required in current ultrafast femtosecond pulsed lasers. This paper mainly focused on gold-plated reflective gratings. We proposed a rectangular grating with high efficiency and broadband under Littrow incidence at the center wavelength of 800nm for TM polarization. Under Littrow incidence, the duty cycle and the groove depth of the grating determine the diffraction efficiency and bandwidth of the gratings. By the Rigorous Coupled Wave Analysis(RCWA) and simulated annealing algorithm, we analyzed the effects of different grating parameters on grating diffraction efficiency and bandwidth. In this paper, we designed a rectangular grating with duty cycle 0.324, groove depth 1466nm and thickness of connection layer 2146nm, respectively. Its diffraction efficiency of the -1 order approached 98% in broadband. And we analyzed the tolerance of our grating to improve the efficiency of the grating. This kind of grating has very important value in the future application of high power laser.
In this paper, we propose a two-dimensional metal-dielectric grating with dielectric nanodisks on a thin gold film structure for refractive index sensing due to its near unity absorption at 1050 nm wavelength. The perfect absorption mainly originates from excitation of the horizontal magnetic dipole mode in the metal-dielectric structure. The results show that the sensitivity and full width half maximum are 560 nm/RIU and 11.13 nm over the sensing range of 1.33 to 1.38, respectively. Obviously, the corresponding figure of merit is calculated to be 50.3 RIU-1, which shows a high sensing performance. Moreover, it also shows excellent performance by measuring the light intensity change in the reflected light at a certain wavelength. The proposed structure has great potential application in biological sensing, integrated photodetectors, chemical applications and so on.
With the rapid development of precision manufacturing, the optical non-contact three-dimensional measurement method for detecting the morphology of tiny objects has gradually become a hot topic with the advantages of high speed, high precision, large measuring range and high repeatability. When the depth of the microgroove reaches a certain range, the general three-dimensional measurement method cannot be used since the depth of focus is usually not deep enough. In this paper, we proposed a new method of detecting based on the grating projection for detecting phase, which introduced a novel diffractive optical device called Dammann zone plate for measuring three-dimensional shape of tiny objects with an extend of focal length. Dammann grating can produce a finite array of uniform intensity spots in the Fourier transforming plane by modulating the transverse position of the transition points of the binary optical phase. Using this feature, the Dammann zone plate takes advantage of the periodic coding details of the Dammann grating for producing an axial multi-focus system with equal intensity in the focusing system when combined with a focusing lens. This experiment, the depth of focus is greatly extended due to the introduction of Dammann zone plate, which can measure deeper grooves. Therefore, we can collect more three-dimensional information of the tiny object with a CCD camera, and then we can obtain more accurate three-dimensional morphologic profile. This method is simple, accurate and robust for practical applications, so it is highly interesting for detecting deeper grooves of tiny objects.
As an important means to obtain three-dimensional depth information of target, optical measurement has been widely used in face recognition, machine manufacturing, aerospace and other related fields in the past decades. Optical three-dimensional imaging and depth measurement is a fast and non-contact method for reconstructing three-dimensional imaging and depth measurement of objects based on optical means and digital image processing analysis. In this paper, a three-dimensional measurement module of transversely rotating combined Dammann grating is proposed, which generates interleaved high-density dot-matrix structured light for three-dimensional imaging and measurement. The measurement module consists of integrated components of laser and beam expander, collimating lens, four transversely rotating combined Dammann gratings with different beam splitting ratios, and objective lens. The laser emits a laser beam which is collimated by a collimating lens. Four Dammann gratings are used to generate four non-staggered dot-matrix by splitting them, and then the high-density staggered projection dot-matrix for three-dimensional measurement and imaging are projected by the objective lens. The measurement module has the advantages of simple structure, high output dot-matrix density, staggered projection dot-matrix edges, and easy integration into mobile devices. This technology may reduce the complexity, number of optical elements, power consumption and cost of structured light projectors in mobile and fixed 3D sensors.