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A 300 mm×500 mm large-area echelle grating with groove density of 79 grooves/mm is fabricated for the spectrometer of the fiber array solar optical telescope (FASOT). This paper focusses on measurement methods of the grating performance. We present a method to evaluate the grating’s stray light intensity, which is measured to a level of 10−4. The directly measured grating efficiency is approximately 90% of the designed value, and an indirect measurement method based on the grating groove profile is proposed. Based on the Rayleigh criterion and the grating diffraction wavefront, a physical optics method and a geometric grating method are proposed and are used to calculate the actual grating resolving power; the calculated results exceed 95% of the grating’s theoretical resolving power. These results show that the CIOMP-6 ruling engine has sufficient precision to fabricate high-quality, large-area echelle gratings.

A mosaicking method for echelles is proposed. The “zero-order” and diffraction-order interference fringes of the echelle can be imaged simultaneously on the detector using a mirror–echelle structure designed. The five-dimensional mosaicking errors are divided into two categories for elimination using the “zero order” and the diffraction order. During the experiments, adjustment devices for the mosaicking errors are installed on two echelles for these two categories to avoid mechanical coupling. As theoretical analysis, we follow the experimental steps to obtain a mosaicked echelle.

Measuring mirror requirements and their impact on groove errors are related to the error compensation strategy for a ruling engine. We analyze why the measuring mirror of the CIOMP-6 engine affects the groove straightness and the grating diffraction wavefront. We study a theoretical model of the relationship between the measuring mirror’s surface shape error and the grating wavefront, propose a requirement for the measuring mirror surface shape error, and reprocess the measuring mirror. Comparative ruling experiments prove that the grating’s wavefront quality at the diffraction order along the groove direction improved significantly after reprocessing of the measuring mirror.

A method for echelle gratings tiling based on lateral shearing interferometry is proposed. Fringe patterns of the grating assembly are generated by a wedge plate. Mosaic errors can be calculated and corrected by observing the working order and its adjacent order. An experimental mosaic of two 50 mm × 50 mm , 79 grooves / mm echelles is aligned to verify the theory. The rms wavefront is better than 0.04 wavelength. Angular and translation sensitivities of less than 1 arcsec and 10 nm are achieved respectively.

In order to provide the guidance for the design and application of echelle gratings, the reason why the diffraction efficiency of the echelle grating can be improved by increasing the groove depth or reducing the apex angle is given. The polarization behaviors of gratings with different groove depths were simulated and analyzed via integral theory. To further demonstrate the polarization behavior, gratings with right and acute apex angles for classical and conical-Littrow incidence were simulated. Experimental polarization behaviors of gratings with 5.1-μm and 6.7-μm groove depths for classical incidence were obtained. The polarization degree of the echelle grating with the 6.7-μm groove depth was 6.5% at 405 nm and 2.52% at 632.8 nm, which smaller than 7.89% at 405 nm and 35.74% at 632.8 nm for the grating with a 5.1-μm groove depth. Therefore, the diffraction efficiency of an echelle grating can be improved by increasing the groove depth or reducing the apex angle, mainly because the polarization degree is restrained.

A measuring method was studied to further improve the manufacturing accuracy of the lead screw. Firstly, factors that can axially displace the screw shaft were analyzed and a relationship between factors and axial displacement was given. The axial displacement of the screw shaft was measured using a laser interferometer, and results show that the variation amplitude of the screw-shaft axial displacement was about 80 nm while the variation period was consistent with the rotation period of the screw shaft. Next, two methods of measuring the manufacturing accuracy of the lead screw were considered: a traditional method that measures the absolute position of the nut and an improved method that measures the displacement between the nut and screw shaft. A No. 4 screw shaft was manufactured under the guidance of results obtained using the improved measuring method. Experimental measurements were then made; results show that the pitch displacement errors obtained using the traditional and improved measuring methods were 0.6 and 0.4 μm, respectively, indicating that the improved measuring method is more exact. Finally, an echelle grating ruled by a grating ruling engine that used the No. 4 screw shaft as a macro-positioning element was introduced. Its excellent parameters indirectly show that the improved measuring method has better accuracy.

The groove shape characteristics of echelle gratings with high diffraction efficiency are investigated. Using the coordinate transformation method (C method), an r-2 aluminum echelle with 79 grooves/mm is optimized through rigorous numerical simulations and shows high diffraction efficiency of 76–81% in the high Littrow orders. A grating is found to be essentially an echelle if it contains a series of reflective facets with a specific tilt angle that are located far from the nonworking facet of the grating and have a deep groove depth; any groove shape that meets these conditions can be called an echelle grating. The underlying mechanism is analyzed phenomenologically using electromagnetic theory. The universal model proposed here, which represents a new cognitive understanding of the concept of the echelle, is ready for use in manufacturing applications and offers a new perspective for the fabrication of these gratings.

A concept for position adjustment of the diamond in a ruling engine to enable nanoscale groove positioning is proposed. Based on this concept, we fabricate a diamond carriage, design an optical path, and propose an appropriate control method. Several high-quality gratings are ruled for spectrometer or interferometer applications. After implementation of the improvements, the maximum intensity of ghosts and scattered light of the echelle grating with 79 grooves/mm is reduced to half of that before the improvement, and the highest achievable groove density is increased from 6000 grooves/mm to 8000 grooves/mm. The grating ruling results indicate that the proposed concept and the related improvements to the engine significantly improve the accuracy of the CIOMP-6 ruling engine.

Combining the mathematical relationships between the grating wavefront and surfaces with the spatial relationships between the two grating wavefront, a mathematical model of the mosaicking errors is established to mosaic gratings. The five-dimensional mosaicking errors will respectively be calculated and then removed by the adjustment mechanisms. Mosaicking experiments are performed by using two gratings. First, by using zeroth order, the longitudinal offset is calculated and removed. Second, by using the diffraction order, the in-plane angle and grating spacing are calculated and removed, while the tip and tilt angles are calculated and removed. And then a mosaic grating is obtained.

The influence of the removal depth of a silicon modification layer on grating structures and mirrors is studied. The removal depth 6-14 μm is the optimization result for Si-modified reaction-sintered silicon carbide (RS-SiC) used as mirror substrates, but the removal depth 9-12 μm is the optimization result for Si-modified RS-SiC used as grating substrates. The diffraction efficiency and stray light of the gratings fabricated in the Si-modified RS-SiC substrates with removal depth 9-12 μm is 90.5%-94% and 5.30×10-7-5.45×10-7, respectively. Additionally, the number and scale of high-reflection points can be used as the basis for judging the removal depth of the Si-modified RS-SiC used as grating substrates. These results and the regularity have guiding significance for the application of Si-modified RS-SiC as a microstructural substrate.

A swing ion-beam etching method to fabricate convex blazed gratings used in shortwave infrared hyperspectral imaging spectrometers is presented. This method solves the consistency problem of blaze angles by swing etching through the meridian direction of the gratings. The mathematical relationship of the curvature, aperture, and diffraction efficiency of convex gratings is studied to demonstrate the limitation of conventional translational lithography and the necessity of swing etching. A geometric model is built to analyze the influence of swinging speed and beam slit width on groove evolution. Convex gratings with a 45.5 gr/mm groove density, 67 mm aperture, 156.88 mm radius of curvature, and 2.2° blaze angle have been fabricated and measured where the peak and average diffraction efficiency in the shortwave infrared band reach 90% and 70%, respectively. Experimental results validate that high-efficiency convex gratings of small blaze angle and high groove consistency can be produced by swing etching, which satisfy the requirements for high spectral resolution and miniaturization of imaging spectrometers.

A field-widened spatial heterodyne Raman spectrometer with a mosaic grating structure is developed for the simultaneous sensitivity enhancement and broadband transmission Raman measurements. We optimize the etendue to maximize the signals collected from the samples by using field-widening prisms and employ two mosaic gratings to achieve broadband operation, covering 5638 cm-1 with 2.865 cm-1 spectral resolution. The signal-to-noise ratios are improved by a factor of more than 11 and show a good stability and fair repeatability. We investigate the effects of the sample thickness and outer layer depth and observe liquids, solids, mixed targets, and anti-Stokes shifts. The instrument exhibits good performance for wide-field, high-resolution broadband transmission Raman measurements.

Grating tiling is an important fabrication technology for large-size gratings. However, when using grating tiling technology to form large-size echelle gratings, the interferometer cannot detect the grating's zero-order diffraction wavefront because the zero-order diffraction light of the echelle grating is weak. This prevents use of the zero-order and non-zero-order diffraction light of the grating to realize separation detection and correction of mosaic errors. To solve this problem, a new method for separation detection and correction of mosaic errors in mosaic gratings based on two detection lights with the same diffraction order but different incident angles is proposed and a mosaic error detection system is designed. Then, the correction steps for mosaic errors are summarized and the error in mosaic error detection system is analyzed. Finally, the measurement uncertainty in detecting the wavefront of the mosaic grating and the mosaic accuracy of the grating wavefront are analyzed. The uncertainty is 0.008λ (λ=632.8 nm) and the mosaic accuracy of the peak-to-valley wavefront is 0.069λ, which shows that high-precision measurements of the wavefront and high-precision mosaic of the wavefront were successfully achieved. The proposed method can be used for the mosaic of all blazed gratings.

The theoretical calculation model for a mosaic error was established based on the plane equation for a grating surface and the relationship equation for a mosaic grating surface. A mosaic grating was obtained based on this model. In the experiment, the mosaic error was calculated based on the diffraction wavefronts of two groups of mosaic gratings that were obtained simultaneously with a Zygo interferometer. The difference between the wavefront of the mosaic grating and the average wavefront of the mosaic grating element was 0 . 031 λ . The maximum far-field intensity of the mosaic grating was 90% of that without an error. This model provides a theoretical basis for the numerical mosaic between gratings. In addition, the mosaic error can be calculated with this model, and the quality of the mosaic grating can be evaluated.

Reduction of groove errors on the grating wavefront caused by the refractive index of air is a critical issue in ruling grating fabrication when using an interferometer to provide position feedback. We establish a mathematical model of the relationship between the grating wavefront and the refractive index of air. We then introduce two methods to measure the air’s refractive index, analyze the effects of temperature, pressure and humidity on the grating wavefront, and use the advantages of the two methods to obtain the groove error compensation value. Comparative ruling experiments prove that grating wavefront quality is significantly improved after compensation of the groove errors caused by the refractive index of air.

As the grating area increases, the non-uniformity of the metal film thickness becomes one of the main factors affecting both the grating surface error and the wavefront of the grating diffraction order. We study the theoretical model of the relationship between the metal film thickness non-uniformity and the grating diffraction wavefront error, analyze the effects of the relevant factors on the thickness of the metal films, and determine the values of these factors using theoretical and experimental methods. We also perform a ruling experiment to verify that the wavefront quality of the grating increases with improvement in the film thickness uniformity.

Groove error is one of the most important factors affecting grating quality and spectral performance. To reduce groove error, we propose a new ruling-tool carriage system based on aerostatic guideways. We design a new blank carriage system with double piezoelectric actuators. We also propose a completely closed-loop servo-control system with a new optical measurement system that can control the position of the diamond relative to the blank. To evaluate our proposed methods, we produced several gratings, including an echelle grating with 79 grooves/mm, a grating with 768 grooves/mm, and a high-density grating with 6000 grooves/mm. The results show that our methods effectively reduce groove error in ruled gratings.

Line curvature error greatly influences the quality of the diffraction wave fronts of machine-ruling gratings. To reduce the line curvature error, we propose a correction method that uses interferometric control. This method uses diffraction wave fronts of symmetrical orders to compute the mean line curvature error of the ruled grating, taking the mean line curvature error as the system line curvature error. To minimize the line curvature error of the grating, a dual-frequency laser interferometer is used as a real-time position feedback for the grating ruling stage, along with using a piezoelectric actuator to adjust the stage positioning to compensate the line curvature error. Our experiments show that the proposed method effectively reduced the peak-to-valley value of the line curvature error, improving the quality of the grating diffraction wave front.

A method to calculate the weight of grating mosaic errors is proposed based on an analytical hierarchy process. An accurate mosaic error tolerance calculation formula is also presented that is useful for large-size grating fabrication by the mosaic method. The grating mosaic error weights and tolerances are analyzed for mosaic echelle gratings. The analytical error weight and tolerance results agree well with the experimental results. The mosaic grating's far-field intensity is 95.8%, which is higher than the 94% value from the simulation results.

Spatial heterodyne Raman spectrometry (SHRS) is a spectral analysis technique used to study material structures and compositions. We propose a multi-grating SHRS system that uses a multi-grating module rather than the single grating used to terminate each arm in traditional spatial heterodyne spectrometry (SHS). The proposed system not only retains the advantages of traditional SHS but also resolves the mutual limitation between system spectral range and resolution. The increased spectral range and resolution that can be achieved in detection are dependent on the number of sub-gratings used in the module. A verification system was built using 130 gr/mm and 150 gr/mm sub-gratings and calibrated. Under different experimental conditions (including laser power, integration time, container material and thickness, pure and mixed samples, and standoff experiments), the backscattered Raman spectra of different types of targets (including organic solutions, inorganic powders, and minerals) were tested. The multi-grating SHRS shows good performance for broad spectral range and high-resolution Raman detection.

Gratings with stray light of 4.99 × 10−7-5.67 × 10−7 and efficiency of 93%-95% in a wavelength range of 1592 nm-1632 nm on Si-surface-modification SiC, fused silica and BK7 have been fabricated by the method of ICP etching-polishing. The CHF3 and SF6 plasma were used to etch a preliminary grating profile. Ar and O2 plasma with low energy were then used to polish the grating to acquire low surface roughness and groove profiles closer to the ideal profiles. The morphologies of the gratings were characterized by AFM. The efficiencies and stray light were measured quantitatively by self-developed equipment. These results show that the ICP etching-polishing method is a promising candidate for production of good quality gratings into common optical materials.

A traditional double monochromatic measurement instrument of diffraction efficiency for a plane grating involves two major problems: one is the differences of output spectrum bandwidths during measurement of a standard reflection mirror and the tested grating; the other is overlapping of diffracted spectra, which influence testing accuracy of diffraction efficiency. In this paper, a new measuring method of diffraction efficiency based on Fourier spectral technology is presented. The mathematical model of diffraction efficiency is first deduced and then verified by ray tracing and Fourier optics simulation. The influences of the moving cube corner's tilt error, lateral shift error, and maximal moving distance error on the measurement accuracy are analyzed in detail. The analyses provide theoretical references for designing diffraction efficiency instruments. Compared with the traditional diffraction efficiency measurement instrument with double monochromator structure, our method not only improves the measurement accuracy of diffraction efficiency but also has the advantage of high luminous flux, high spectral resolution, multiwavelength measurement in mean time, and high wavenumber accuracy.

A new broadband Raman spectrometer has been developed, to the best of our knowledge, using a double-echelle spatial heterodyne Raman spectrometer (DESHRS). The instrument is constructed by using two echelle gratings. Masks are used to remove the shadow ghosts caused by the different orders of the two echelle gratings. Raman spectra of inorganic solid targets and methanol are given, and Raman shifts of up to 3000 cm−1 are obtained by the DESHRS. The instrument has shown that a broadband coverage and high resolution can be achieved simultaneously to meet the requirements of Raman measurements, covering 3590 cm−1 with 1.21 cm−1 spectral resolution.

A method of eliminating echelle mosaicking errors using a single-interferometer system combined with a mirror-echelle structure and double-angle incident light is proposed. Coplanar and in-plane mosaicking errors are, respectively, removed using interference fringes at zero order and diffraction order, and double-angle incidence light is exploited to erase the longitudinal offset. Two mirror-echelle structures, both with aluminum reserved for a mirror on the echelle plane to receive the double-angle incident light, are designed. The relationship between mosaicking error and the optical path difference is established. The evolution of the interference fringe pattern of mosaicking process is simulated, and a mosaicking experiment is then conducted following the simulation.

Spatial heterodyne Raman spectroscopy is a spectroscopic detection technique that is particularly suitable for Raman measurements. The spectral range of traditional spatial heterodyne Raman spectrometer (SHRS) is limited by its spectral resolution and the number of detector elements. We propose an SHRS with an echelle-mirror structure that employs multiple diffraction orders to achieve a broad spectral coverage and high spectral resolution simultaneously. This SHRS is used to obtain the Raman spectra of organic liquids, inorganic solid targets, and mixed targets. Observations of aqueous solutions, and minerals are presented. In addition, anti-Stokes Raman shifts are also presented. The proposed SHRS technique shows good performance for broadband, high-resolution Raman measurements.

A novel technology to manufacture holographic ion beam etched diffraction gratings based on surface thermokinematics is presented. The surface roughness of photoresist gratings is solved by this technology. According to this technology, a holographic ion beam etched blazed grating of 1200 l/mm for use in the ultraviolet region is manufactured. The experimental results show that the grating has good surface quality, low stray light and high diffraction efficiency. In addition, the performance of thes gratings satisfies the operating requirements of ultraviolet spectrograph.

The inductively coupled plasma atomic emission spectrometry (ICP-AES) has always attracted great interest and is widely used for routine elemental analysis. While one drawback of this technique is the fact that conventional Czerny- Turner spectrographs in combination with CCD cameras are very limited either in terms of spectral resolution or in terms of simultaneously detectable spectral range. A cross-dispersion system with echelle grating and prism has therefore been developed, and the spectral image is directed by large area charge coupled device (CCD). This configuration meets the needs of atomic emission spectroscopy well, since it has many benefits including high resolving power, spectral coverage, high sensitivity, and high optical throughput. While, because the limitation of the development of detectors, it is difficult to complete wide spectral coverage measurement. Due to the improvements in optical design, this system can detect the wide spectral coverage from 180nm to 900nm simply by rotating the prism, and these two ranges are 180nm- 260nm and 210nm-900nm, with a high resolution 0.009nm@200nm. The detection of different elements only needs to choose appropriate wavelength coverage, thus lots of elements can be analyzed within quite short time. The novel optical design of this instrument is presented in this paper and its merits are discussed. The optical spectral resolution and the precision of wavelength calibration are found to be satisfactory and within design goals. Experiments show that the ICPAES with echelle spectrometer is available to detect multiple elements within a short time correctly, and the wavelength precision is better than 0.01nm.

Ruling of echelles and gratings by the torque equilibrium method is proposed to eliminate corrugated grating lines, rough blazed grating surfaces, and complex fabrication work such as step-by-step diamond tool deflection. A mathematical model of the torque equilibrium between the diamond tool and the metallic film during the ruling process is deduced to realize optimized diamond tool geometrical parameter design. Then, two echelles with identical areas of 80 mm×100 mm are separately ruled using the traditional deflecting tool ruling method and the proposed method, and the scatter light results for the two echelles are 9.6×10−4 and 3.1×10−4, respectively.

An interference method to remove all mosaic grating errors using a phase-difference reference window without compensation for coupled mosaic errors or analyzing the far-field diffraction intensity patterns is proposed. The reference window is achieved by adding a small-aperture prism; therefore, the incident light on the mosaic gratings contains two different angles of incidence and optical paths, eliminating the uncertainty of longitudinal mosaic error in the interferometer. The mathematical model of the method is established and optical arrangement is presented. Interference fringes with the reference window and alignment process are simulated and the accuracy of mosaic errors are analyzed. The experimental and simulation results show that our method can eliminate longitudinal mosaic error and all other mosaic grating errors. The accuracy of angle mosaic errors can be less than 1 μrad and position mosaic errors can be to the nanometer level. Compared with the far-field diffraction intensity patterns method, our method reduces the complexity of the optical structure and ensures measurement accuracy.

The designs of 300 mm ruling engine producing gratings and echelles under interferometric control (CIOMP-2) are presented. A new ruling-tool carriage system and its driving mechanism—which are easy to manufacture—are proposed. A new blank carriage system, controlled by a dual-frequency laser interferometer and a piezoelectric actuator, is designed. The CIOMP-2 ruling engine can now rule grating blanks with dimensions up to 300 mm×300 mm, and mainly rules gratings with grating constants between 10 and 2400 lines/mm. The wavelength range of CIOMP-2 gratings is from ultraviolet to mid-infrared wavelengths. Experiments show that the new ruling-tool carriage system works well and stability of motion is improved with the help of a flexure-hinge structure, and the threefold standard deviation values of the blank carriage positioning errors are less than ∼5 nm. For 600 line/mm gratings (diffraction order m=−1), the scatter intensities and ghosts reach 10−5 of the maximum intensity. The scatter intensities and ghost of gratings ruled with CIOMP-2 are low, and no Rowland ghosts are visible. The gratings ruled by CIOMP-2 have high diffraction efficiency and resolving power. CIOMP-2 can also produce varied-line-space, bend-line, and aberration-reducing gratings and echelles.

In order to solve the problem that the grating quality cannot be monitored directly in real time, we provided a method based on Rayleigh criterion with our designing optical measurement structure to measure yaw and displacement errors of a grating ruling machine feeding system. Gratings are ruled with or without errors correction by the real-time monitoring system . It shows that the resolution obtained without errors correction is reduced from 99.97% to 87.47% of theoretical value, while the resolution obtained with errors correction is stable, remaining at 99.99%–97.21%. The experimental result is that the grating quality can be guaranteed by monitoring grating resolution in real time.