Reflection Gratings Research Articles

A geostationary orbit microwave multi-channel radiometer

The geostationary orbit microwave multi-channel radiometer has the advantages of high real-time performance and large coverage, which plays an important role in typhoon, strong precipitation detection, and medium-to-short-term meteorological/oceanic forecasting. However, due to the difficulty in engineering development of the payload, its application on-orbit has not yet been achieved at present. To satisfy the requirements of fine and quantitative application of satellite observation data, a geostationary orbit microwave multi-channel radiometer with a 10-m-caliber is developed, in which the spatial resolution at horizontal polarization is better than 24 km at 54 GHz. In geostationary orbit microwave multi-channel radiometer, a quasi-optical feed network covering nearly 28 frequency octave bands and ranging from 23.8 to 664 GHz is proposed to solve the technical problem of multi-frequency sharing in the system. Meanwhile, a high-precision reflector preparation method and a high-precision unfolding scheme are proposed, which are considered as a solution for the large-diameter reflector with a high maintaining surface accuracy. A high-precision antenna prototype with 0.54-m is developed, and the tests are performed to verify the key technologies, such as the preparation of high-precision grating reflectors at the micron level, high surface accuracy detection, and sub-millimeter wave antenna electrical performance testing. The results indicate that measured main beam efficiency of the 664 GHz antenna is better than 95.5%. In addition, the system sensitivity is greater than 1.5 K, and the calibration accuracy is better than 1.8 K, according to the results of an analysis of the multi-channel radiometer’s essential parameters and calibration errors.

Portable Raman Spectrometers: How Small Can They Get?

Portable Raman spectrometers have become smaller over the last 20 years, while their performance has increased. This has been made possible by closer coupling of all the components, use of transmission gratings rather than reflection gratings, and general advances in electronics, displays, and battery technologies. An obvious question to ask is whether this trend can continue. This paper describes the technologies and evolution of these instruments, existing limitations, the current landscape of miniature Raman spectrometers, and the state of the art. Finally, the paper also looks at what emerging technologies could be applied in this area, and how those could lead to new applications

Experimental and Modeled Output Characteristics of a Compact, Passively Q-Switched Tm:YLF Laser

We measure the output characteristics of a compact, laser diode end-pumped Tm:YLF laser, operated in continuous wave (CW) mode, or passively Q-switched (PQS) using various Cr2+:ZnS saturable absorbers. A numerical Finite-Difference Beam Propagation Method (FD-BPM) is developed and used to model the laser CW and pulsed performance. Good agreement between the experiment and simulated output is demonstrated. The 39 mm-long laser resonator utilizes a 20.2 mm-long Tm:YLF crystal, a 1908 nm volume Bragg grating (VBG) reflector to restrict the emission wavelength, and an intra-cavity negative lens to reduce the energy fluence in the saturable absorber. A laser utilizing a Cr2+:ZnS saturable absorber with 91.9% unsaturated transmission generates 9.8 mJ PQS pulses with 8.7 ns full-width-half-maximum (FWHM) pulse duration. Maximum average output powers of 6.1 W and 6.5 W are generated in PQS and CW operation, respectively.

Progenitor Constraint with Circumstellar Material for the Magnetar-hosting Supernova Remnant RCW 103

Stellar winds blown out from massive stars (≳10 M ⊙) contain precious information on the progenitor itself, and in this context the most important elements are carbon (C), nitrogen (N), and oxygen (O), which are produced by the CNO cycle in the H-burning layer. Although their X-ray fluorescence lines are expected to be detected in swept-up shock-heated circumstellar materials in supernova remnants, those of C and N have been particularly difficult to detect so far. Here, we present high-resolution spectroscopy of the young magnetar-hosting supernova remnant RCW 103 with the Reflection Grating Spectrometer on board XMM-Newton and report on the detection of the N vii Lyα (0.50 keV) line for the first time. By comparing the obtained abundance ratio of N to O (N/O = 3.8 ± 0.1) with various stellar evolution models, we show that the progenitor of RCW 103 is likely to have a low mass (10–12 M ⊙) and medium rotation velocity (≲100 km s−1). The results also rule out the possibility of dynamo effects in massive (≥35 M ⊙) stars as a mechanism for forming the associated magnetar 1E 161348−5055. Our method is useful for estimating various progenitor parameters for future missions with microcalorimeters such as XRISM and Athena.

Recovery of a highly reflective Bragg grating in DPDS-doped polymer optical fiber by thermal annealing.

We report fiber Bragg grating manufacturing in poly(methyl methacrylate) (PMMA)-based polymer optical fibers (POFs) with a diphenyl disulfide (DPDS)-doped core by means of a 266 nm pulsed laser and the phase mask technique. Gratings were inscribed with different pulse energies ranging from 2.2 mJ to 2.7 mJ. For the latter, the grating reflectivity reached 91% upon 18-pulse illumination. Though the as-fabricated gratings decayed, they were recovered by post-annealing at 80°C for 1 day, after which they showed an even higher reflectivity of up to 98%. This methodology for the fabrication of highly reflective gratings could be applied for the production of high-quality tilted fiber Bragg gratings (TFBGs) in POFs for biochemical applications.

Improving the Angular Visibility of Photopolymer-Based Reflection Holograms for Sensing Applications.

Volume reflection hologram-based sensors are designed to visibly change colour in response to a target stressor or analyte. However, reflection holograms fabricated in thick photopolymer films are highly angularly selective, making these sensors challenging to view and interpret by non-experts. Here, the use of speckle holography to improve the visibility of reflection holograms is presented. A novel recording approach combining speckle recording techniques with Denisyuk reflection recording geometry is described. The recorded speckle reflection grating operates as a series of multiplexed reflection gratings with a range of spatial frequencies, capable of reflecting light at a wider range of angles. A comparative study of the angular and wavelength selectivity of speckle and standard reflection gratings was conducted. The FWHM of the angular selectivity curves of the speckle reflection gratings is doubled (4°) in comparison to standard 4500 lines/mm reflection gratings (2°). The wavelength selectivity FWHM is also doubled from 4.2 to 8.6 nm. The comparative ability of the speckle and standard reflection gratings to act as colour-changing compressional pressure sensors in the 0.88-5.31 MPa range is described. Finally, we present a prototype reflection hologram viewer which enables the easy observation of angularly specific reflection holograms by non-experts.

Advantages of out-of-plane pulse compression gratings.

Diffraction gratings for pulse compression generally perform best at the Littrow angle, but reflection gratings require a nonzero deviation angle to separate the incident and diffracted beams, so they cannot be used at the Littrow angle. In this paper, we show both theoretically and experimentally that most practical multilayer dielectric (MLD) and gold reflection grating designs can be used with quite substantial beam-deviation angles-as large as even 30°-by mounting the grating out-of-plane and choosing the optimal polarization. The impact of polarization when mounting out-of-plane is explained and quantified.

Volumetric thermochemical laser writing of nanostructured reflective diffraction gratings on a dual-layer Zr/SiO2 material

Volumetric thermochemical laser writing of nanostructured reflective diffraction gratings on a dual-layer Zr/SiO₂ material

Stable single-mode operation of distributed feedback quantum cascade laser under high current via a grating reflector

Abstract We report on an index-coupled distributed feedback (DFB) quantum cascade lasers (QCLs) of high single-mode stability by using of a grating reflector (GR) to reflect effectively light of a specific wavelength. Fabrications of the QCLs were performed with λ∕4 equivalent phase shift (EPS) or sampled Moiré grating (SMG) structure, which regulates the light intensity distribution in the cavity and coupling strength. Both EPS-GR and SMG-GR QCLs demonstrate a high emission wavelength precision and a side-mode-suppression-ratio (SMSR) of 24.5 dB at the injection current of 5 A and the pulse width of 5 μs, offering considerable output power even at the edge of the gain spectrum. Furthermore, we investigated the arrays of EPS-GR and SMG-GR QCLs with lower threshold current and higher output power by introducing semi-insulated InP (Fe) ranging from 8.25 to 8.67 μm and 8.16–8.63 μm, respectively. The present QCLs via a GR are prospective for applications requiring single-mode stability and wide tunability.

Searching for the warm-hot intergalactic medium usingXMM–Newtonhigh-resolution X-ray spectra

ABSTRACTThe problem of missing baryons in the local universe remains an open question. One proposed alternative is that at low redshifts missing baryons are in the form of the warm-hot intergalactic medium (WHIM). In order to test this idea, we present a detailed analysis of X-ray high-resolution spectra of six extragalactic sources, Mrk 421, 1ES 1028+511, 1ES 1553+113, H2356−309, PKS 0558−504, and PG 1116+215, obtained with the XMM–Newton Reflection Grating Spectrometer to search for signals of WHIM and/or circumgalactic medium X-ray-absorbing gas. We fit the X-ray absorption with the IONeq model, allowing us to take into account the presence of X-ray spectral features due to the multiphase component of the local interstellar medium (ISM). An additional IONeq component is included to model the WHIM absorption, instead of the traditional Gaussian absorption line modelling. We found no statistical improvement in the fits when including such component in any of the sources, concluding that we can safely reject a successful detection of WHIM absorbers towards these lines of sights. Our simulation shows that the presence of the multiphase ISM absorption features prevents the detection of low-redshift WHIM absorption features in the >17 Å spectral region for moderate exposures using high-resolution spectra.

Hidden Cooling Flows in clusters of Galaxies II: a wider sample

ABSTRACT We have recently uncovered Hidden Cooling Flows (HCFs) in the XMM Reflection Grating Spectrometer spectra of three clusters of galaxies; Centaurus, Perseus, and A1835. Here, we search for them in a wider sample of objects: the X-ray brightest group NGC 5044; four moderate X-ray luminosity clusters Sersic 159, A262, A2052, and RX J0821; and three high X-ray luminosity clusters RX J1532, MACS 1931, and the Phoenix cluster. Finally, we examine two Virgo elliptical galaxies, M49 and M84. All statistically allow the addition of an HCF. We find a significant detection of an HCF in six clusters and two elliptical galaxies. The hidden mass cooling rates are $5{\!-\!}40\hbox{$\hbox{$\rm \, {\rm M}_{\odot }$}{\rm \, yr}^{-1}\, $}$ for the normal clusters, $1000\hbox{$\hbox{$\rm \, {\rm M}_{\odot }$}{\rm \, yr}^{-1}\, $}$ or more for the extreme clusters, and $1{\!-\!}2\hbox{$\hbox{$\rm \, {\rm M}_{\odot }$}{\rm \, yr}^{-1}\, $}$ for the elliptical galaxies. We discuss the implications of the results for the composition of the innermost parts of the massive host galaxies and look forward to future observations.

An ultrahigh-resolution spectrometer using parallel double gratings

This paper describes a Parallel-Double-Grating Spectrometer (PDGS) with ultrahigh resolution. Two plane reflection gratings are placed in parallel and staggered to form a dispersive component, through which the light passes multiple times, which greatly improves the dispersion capability of the spectrometer, and therefore the resolution. The diffraction characteristics of the dispersive component and the mathematical model of the PDGS are studied. The results of simulation show that using two reflection gratings with a groove density of 168 gr/mm, combined with spectral splicing technology, the PDGS can achieve a measurement waveband from 450 nm to 610 nm with a resolution better than 30.88 pm. Modifying the structural parameters of the PDGS extends the applicability of the optical path structure to spectral bands from ultraviolet to infrared.

Reflective structure for phase-shifted fiber Bragg grating.

A novel, to the best of our kowledge, reflective phase-shifted fiber Bragg grating (R-PS-FBG) structure composed of a conventional fiber Bragg grating (FBG) and a micromirror with an air gap between them is proposed. The R-PS-FBG may be regarded as consisting of a Fabry-Perot interferometer and a phase-shifted fiber Bragg grating (PS-FBG), and its reflection and transmission spectra are investigated numerically and experimentally for different mirror reflectances and gap widths. The R-PS-FBG can be implemented easily and could be used in optical spectrum filtering, wavelength tuning, and multiparameter sensing with better sensitivity and resolution.

A broadband picometer resolution visible CCD spectrometer based on virtually imaged phased array technology.

Coincidental realization of broadband spectral coverage and high resolution in one spectrometer system has always been a challenge. Here, we report the development of a high-resolution visible CCD spectrometer based on the virtually imaged phase array (VIPA) technique. By using a thin glass plate and a reflective grating, a two-dimensional cross-dispersion was realized. A broadband coverage of ∼14.94 THz and a high resolution of ∼1 GHz at 632.996 nm were achieved with a simple structure. The effects of the surface quality of VIPA etalon, the pixel size of the CCD camera, the pinhole size of the input beam, and the focal length of the imaging lens on the resolution of the spectrometer and the transverse spot size on the detector plane were considered. A comparison between the experimental results by changing the imaging lens and the theoretical calculation results proved a better simulation of these two parameters, which is a helpful contribution to the design and construction of a VIPA spectrometer. The developed spectrometer will provide a useful tool for the study of high-resolution spectroscopy and for simultaneous multi-species trace detection.

Wide band UV/Vis/NIR blazed-binary reflective gratings for spectro-imagers: two lithographic technologies investigation

We report on subwavelength reflective gratings for hyperspectral applications operating in a very large spectral band (340–1040 nm). Our study concerns a blazed-binary grating having a period of 30 μm and composed of 2D subwavelength structures with size from 120 nm to 350 nm. We demonstrate the manufacturing of the gratings on 3″ wafers by two lithography technologies (e-beam and nanoimprint) followed by classical dry etching process. Optical measurements show that the subwavelength grating approach enables a broadband efficiency, polarization behaviour and wavefront quality improvement with respect to the requirements for the next generation of spectro-imagers for Earth observation missions. An outlook towards spherical substrate based on nanoimprint lithography is also reported with the results of mixed features replication (holes and pillars in the range of 160–330 nm) on a 540 mm concave substrate which demonstrate uniformity and accuracy capabilities over 3″ surface.

Internal mechanism of perfect-reflector-backed dielectric gratings to achieve high diffraction efficiency

The work started 20 years ago [Appl. Opt. 42, 6255 (2003)] investigating the physical mechanism of multilayer dielectric reflection gratings to achieve 100% diffraction efficiency is extended to offer much deeper insight than before. How different diffraction amplitudes of the top surface corrugation contribute to the −1st-order efficiency of such a grating is shown analytically using a minimum set of real parameters. The two diffraction amplitudes transmitted through the corrugation play a dominant role in enabling DE = 100%. The necessary and sufficient condition for 100% efficiency is derived, and a very simple sufficient condition is also given. Moreover, the role of the reflection phase of the perfect-reflector, including the contribution due to optical path between the corrugation and the reflector, is emphasized.

On the Use of Haloalkane/Acrylate-Based Holographic Gratings as Compression and Rotation Sensors.

In this work, we test the effectiveness of using highly transparent holographic phase reflection and transmission volume gratings based on multifunctional acrylates as linear compression and rotation sensors. The gratings are recorded in a holographic mixture based on multi-reticulated acrylate and haloalkanes. To activate the photo-polymerization process, we used a mixture of 6-oxocamphore and rhodamine 6G. The mixture is a simplified version of the mixture used in previous works and shows some interesting features mainly in connection with the different roles played by the rhodamine 6G dye at different writing wavelengths λ = 532 nm and λ = 460 nm. Regarding reflection gratings, the maximum achieved diffraction efficiency is ≈50% and their use as linear compression sensors produces a shift in the reflection peak of 2 nm. Following the removal of compression, the grating slowly returns to the initial state. Regarding transmission gratings, the maximum achieved diffraction efficiency is ≈45% and they demonstrate very high sensitivity to even small rotations in a free-standing configuration.

Nanoscale morphology and thermal properties of low insertion loss fiber Bragg gratings produced using the phase mask technique and a single femtosecond laser pulse.

Fiber Bragg gratings with a very low insertion loss are inscribed using the phase mask technique and a single infrared (800 nm) femtosecond laser pulse. The morphology of the resultant light-induced structural changes in the Ge-doped silica fiber (SMF-28) is analyzed using scanning electron microscopy. The electron microscopy images reveal that each Bragg grating period incorporates an elongated micropore embedded in a region of homogeneous material modification. The Bragg wavelength drift and reflectivity of fiber Bragg gratings produced with single pulses having the same energy but different duration (80 fs and 350 fs) are monitored for 1000 hours in the course of isothermal annealing at 1000°C. The annealing data demonstrate that both the isothermal Bragg wavelength drift and the decrease in the reflectivity of the fiber Bragg gratings under test are statistically slower for the 350 fs inscription pulses.

Slope error correction on X-ray reflection gratings by a variation of the local line density.

The patterning of x-ray grating surfaces by electron-beam lithography offers large flexibility to realize complex optical functionalities. Here, we report on a proof-of-principle experiment to demonstrate the correction of slope errors of the substrates by modulating the local density of the grating lines. A surface error map of a test substrate was determined by optical metrology and served as the basis for an aligned exposure of a corrected grating pattern made by electron-beam lithography. The correction is done by a variation of the local line density in order to compensate for the local surface error. Measurements with synchrotron radiation and simulations in the soft X-ray range confirm that the effects of slope errors were strongly reduced over an extended wavelength range.

Broadband radiation pressure on a small period diffractive film.

The p-polarization component of radiation pressure force from an unpolarized blackbody light source is predicted by the use of a Maxwell equation solver for a right triangular prism grating of period 2 μm and refractive index 3.5. The transmitted and reflected angular scattering distributions are found to qualitatively agree with diffraction theory: At relatively short wavelengths the transmitted light is concentrated near the refraction angle, and reflected light is concentrated near the reflection angle. Owing to diffraction and multiple internal reflections, however, the spectral irradiance of transmitted and reflected light was found to significantly vary with wavelength. We found that the high value of the refractive index produced a large fraction of reflected light, thereby reducing the net transverse component of radiation pressure force. These results suggest that low index transmission gratings, anti-reflection coatings, optimized metasurface films, or reflection gratings should be explored for future solar sailing missions.