Μm Band Research Articles

Improving discrimination between clouds and optically thick aerosol plumes in geostationary satellite data

Abstract. Cloud masking is a key initial step in the retrieval of geophysical properties from satellite data. Despite decades of research, problems still exist of over- or underdetection of clouds. High aerosol loadings, in particular from dust storms or fires, are often classified as clouds, and vice versa. In this paper, we present a cloud mask created using machine learning for the Advanced Himawari Imager (AHI) aboard Himawari-8. In order to train the algorithm, a parallax-corrected collocated data set was created from AHI and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) lidar data. Artificial neural networks (ANNs) were trained on the collocated data to identify clouds in AHI scenes. The resulting neural network (NN) cloud masks are validated and compared to cloud masks produced by the Japanese Meteorological Association (JMA) and the Bureau of Meteorology (BoM) for a number of different solar and viewing geometries, surface types and air masses. Here, five case studies covering a range of challenging scenarios for cloud masks are also presented to demonstrate the performance of the masking algorithm. The NN mask shows a lower false positive rate (FPR) for an equivalent true positive rate (TPR) across all categories, with FPRs of 0.160 and 0.259 for the NN and JMA masks, respectively, and 0.363 and 0.506 for the NN and BoM masks, respectively, at equivalent TPR values. This indicates the NN mask accurately identifies 1.13 and 1.29 times as many non-cloud pixels for the equivalent hit rate when compared to the JMA and BoM masks, respectively. The NN mask was shown to be particularly effective in distinguishing thick aerosol plumes from cloud, most likely due to the inclusion of the 0.47 and 0.51 µm bands. The NN cloud mask shows an improvement over current operational cloud masks in most scenarios, and it is suggested that improvements to current operational cloud masks could be made by including the 0.47 and 0.51 µm bands. The collocated data are made available to facilitate future research.

Search for carbon-bearing compounds on low-albedo asteroids

Abstract In this work we aim to investigate the presence of absorption bands around 3.4 μm in the infrared spectra of primitive asteroids. We collected the published reflectance spectra of low-albedo asteroids from the literature and analyzed the 2.4-3.8 μm region using the same techniques. From the initial dataset of 92 asteroids, we restricted our analysis to 42 spectra of low-albedo asteroids with a good signal-to-noise (S/N) ratio and we found the absorption feature around 3.4 μm in the spectra of 16 objects. For objects that are classified by the 3 μm band into the ’rounded’, Ceres-like, and Europa-like groups, the depth of the 3.4 μm feature is strongly correlated with that of the 3 μm band. The majority of objects in our dataset not showing the 3.4 μm absorption band have lower S/N spectra and belong to Ch or Chg classes, while asteroids with a detected 3.4 μm bands mostly belong to C, B, and also P types. Additionally, asteroids with a detected 3.4 μm band tend to have a lower albedo, redder J-K colors, and more neutral U-V colors. We observe that the analyzed objects larger than ∼300 km in diameter show features due to carbon-bearing materials, which could be explained by their higher S/N ratio in our dataset. Finally, we found that the distributions of asteroids showing the 3.4 μm feature appear to be shifted towards larger distances from the Sun compared to those not showing this band.

Polycyclic Aromatic Hydrocarbon emission model in photodissociation regions – I. Application to the 3.3, 6.2, and 11.2 μm bands

ABSTRACT We present a charge distribution based model that computes the infrared spectrum of polycyclic aromatic hydrocarbon (PAH) molecules using recent measurements or quantum chemical calculations of specific PAHs. The model is applied to a sample of well-studied photodissociation regions (PDRs) with well-determined physical conditions (the radiation field strength, G0, electron density ne, and the gas temperature, Tgas). Specifically, we modelled the emission of five PAHs ranging in size from 18 to 96 carbon atoms, over a range of physical conditions characterized by the ionization parameter $\gamma = G_{0}\times T_{\rm gas}^{1/2}/n_{e}$. The anions emerge as the dominant charge carriers in low γ (<2 × 102) environments, neutrals in the intermediate γ (103 – 104) environments, and cations in the high γ (>105) environments. Furthermore, the PAH anions and cations exhibit similar spectral characteristics. The similarity in the cationic and anionic spectra translates into the interpretation of the 6.2/(11.0+11.2) band ratio, with high values of this ratio associated with large contributions from either cations or anions. The model’s predicted values of 6.2/(11.0+11.2) and 3.3/6.2 compared well to the observations in the PDRs NGC 7023, NGC 2023, the horsehead nebula, the Orion bar, and the diffuse interstellar medium, demonstrating that changes in the charge state can account for the variations in the observed PAH emission. We also reassess the diagnostic potential of the 6.2/(11.0+11.2) versus 3.3/(11.0+11.2) ratios and show that without any prior knowledge about γ, the 3.3/(11.0+11.2) can predict the PAH size, but the 6.2/(11.0 + 11.2) cannot predict the γ of the astrophysical environment.

Chromospheric Carbon Monoxide Formation around a Solar Pore

We present observations of NOAA AR 11159, obtained on 2011 February 14 in the 4.7 μm band of carbon monoxide (CO) and coordinated with spectroscopic imaging of three atomic lines (Na i 5896 Å, Fe i 7090 Å, and Ca ii 8542 Å) which sample heights from the mid-photosphere to the chromosphere. Phase-difference spectra between the observed spectral lines instead indicate that the CO lines form at z ≈ 530−650 km in the quiet Sun. During the two hours of observations, seven long-lived cooling events (“cold bubbles”) were observed in CO in the region surrounding a large pore, but were not visible in the three atomic lines. These events show self-similar temporal evolution with time scales consistent with the chemical formation rate of CO at z ≈ 1000 km. Due to the lack of such features in the surrounding quiet Sun, we hypothesize that the magnetic canopy field surrounding the pore, which suppresses the upward propagation of acoustic waves into the chromosphere and the subsequent formation of shocks, depresses the rate of acoustic heating and allows CO to condense and cool the atmosphere at those heights. These “cold bubbles” may be a source of the chromospheric CO that produces the unexpectedly high (z ≈ 1000 km) limb extensions seen in the stronger CO lines, and may provide a unique opportunity to study this enigmatic component of the solar atmosphere in spatially resolved observations.

Numerical Investigation of the Flow and Infrared Radiation Characteristics of Nozzles with Transverse Jets of Different Shapes

The hot jet of an aero engine is one of the main radiation sources of infrared detectors in 3–5 microwave bands. Transverse jets were introduced into a hot jet to enhance mixing and reduce the infrared radiation characteristics. This proved to be a high-efficiency and low-resistance infrared suppression technology. The steady-state distribution of temperature data was simulated, which was needed in the thermal radiation calculation. The radiation characteristics were calculated based on the anti-Monte Carlo method in 3–5 microwave bands. The mechanics of enhanced mixing by a rectangular nozzle or transverse jets was investigated with the LES simulation. Compared with an axisymmetric nozzle, a rectangular nozzle induced abundant counter-rotating vortex pairs (CVP), hairpins, shears, and helical vortexes, which resulted in significant mixing enhancement and infrared radiation decrease of the hot jets. Further, circumferential transverse jets of different types were introduced downstream of the nozzle. These jets enhanced the mixing and reduced the infrared radiation in the 3–5 µm band. The mixing characteristics of these different schemes were studied in detail. Large-scale vortices formed on the windward portion of the hot jet boundary under the effect of the transverse jets, which caused strong CVP structures. They also resulted in hairpin vortexes, shear vortexes, and helical vortexes appearing earlier and occurring more frequently than with nozzles without transverse jets. The enhanced mixing caused by the transverse jets led to an increase in temperature decay and a decrease in infrared radiation in the 3–5 µm band. Further, transvers jets of different geometrical shapes (rectangular, cube, and circular schemes) achieved different mixing characteristics, and the rectangular transverse jets allowed the most significant mixing for the largest Q criterion value.

Spectral evidence for a pyroclastic mantle over the Tacquet formation and Menelaus domes of southwest Mare Serenitatis

The Tacquet Formation (TF) was first identified in geologic mapping of southern Mare Serenitatis as a distinct low albedo region split by the linear Rimae Menelaus rilles. A distinct western dome, split by a linear rille and less distinct eastern dome (the Menelaus domes) are also present within the TF. Previous Earth-based radar analyses showed that the TF has a lower circular polarization ratio consistent with a pyroclastic mantle. In this study, compositional and spectroscopic parameters were derived from Moon Mineralogy Mapper (M3) data. Lunar Reconnaissance Orbiter Camera Wide Angle Camera (LROC WAC) and SELENE Kaguya Multiband Imager (MI) multispectral data were also utilized. FeO derived from MI data for the TF and Menelaus domes was elevated at levels consistent with pyroclastic glasses. While not diagnostic of pyroclastics, TiO2 derived from LROC WAC data over the TF and Menelaus domes was also elevated relative to the background materials. Analysis of 1 and 2 μm band parameters also show the TF and Menelaus domes as being distinct with a band center moderately longer than 1 μm and 2 μm band center shorter than the surroundings, characteristics consistent with pyroclastic glass and/or increased ilmenite. M3 data thermally corrected via two different thermal correction approaches indicate a moderately deeper band in the 3 μm region indicative of OH and/or H2O, a characteristic that is also potentially associated with pyroclastic deposits. These compositional findings are consistent with the Earth-based radar data suggesting that the TF is a pyroclastic mantle and potentially represents a previously unrecognized sub-class of pyroclastic deposits associated with lunar volcanic domes.

Preparation of infrared high radiation coatings from modified spinel NiFe2O4 and its energy saving applications

The NiFe spinel material itself has good thermal stability and emissivity and can be prepared as an infrared high radiation coating for energy saving applications in industrial high temperature furnace applications. In this study, Cr3+ and Cu2+ doped spinel NiFe2O4 was prepared by solid phase reaction at 1250 °C for 3 h and the microstructure and physicochemical properties of the powder and coating were characterised by XRD, SEM, EDS and IR radiometry. The effect of Cr3+ and Cu2+ doping on the infrared emissivity of spinel NiFe2O4 was investigated and energy saving assessment was carried out in a resistance furnace. The results show that the doping of Cr3+ and Cu2+ can significantly affect the emissivity of spinel powders in the 2.5–10 μm band, and the coatings prepared from the four powders have an emissivity of up to 0.95 in the 2.5–10 μm band. using this high temperature infrared radiation energy saving coating in a resistance furnace resulted in significant energy savings compared to no coating. The furnace was tested for energy saving by holding the furnace for 2 h and 5 h, and the energy saving efficiency reached 20.7% and 17.0% respectively. The coating was subjected to 10 thermal shock tests from room temperature to 700 °C. The coating bonded well and had good thermal shock resistance. Therefore, the coating has wide application prospects for energy saving applications in the field of industrial high temperature furnaces.

Ultralong wavelength operation of a tunable multiwavelength Brillouin-Raman fiber laser in 1.65 μm band

A tunable multiwavelength Brillouin-Raman fiber laser (MW-BRFL) operated at an ultralong wavelength band (U-band) is presented in this work. The MW-BRFL was configured in a full-open linear cavity consisting of 11.2 km long dispersion compensating fiber that functioned as a Brillouin frequency shifter and Raman amplification gain medium. At Raman and Brillouin pump powers of 930 mW and 11.8 dBm, respectively, a stable multiwavelength generation with wavelength spacing of 0.17 nm was generated over a wavelength span of 53 nm. The generated channels covered a spectral range of 1630–1683 nm corresponding to 314 channels. The channels could also be tuned over 10 nm with an average optical signal-to-noise ratio greater than 26 dB. The laser system exhibited power fluctuation of less than 0.25 dB over 3 h. In a nutshell, the proposed MW-BRFL is promising with respect to its performance, simplicity and flexibility.

GeSn Waveguide Photodetectors with Vertical p–i–n Heterostructure for Integrated Photonics in the 2 μm Wavelength Band

The 2 μm wavelength band (1800–2100 nm) emerges as a promising candidate for next‐generation optical communication. As a result, silicon photonic platforms acquire great interest since they offer the ultimate minimization of photonic systems for 2 μm band applications. However, the large bandgap and indirectness of the band structure of the conventional SiGe alloy prevent their utilization for efficient photodetection in the 2 μm wavelength band. To overcome this drawback, complementary metal‐oxide semiconductor (CMOS)‐compatible GeSn waveguide photodetectors (WGPDs) with a vertical p–i–n heterojunction configuration that can operate in the 2 μm wavelength band is demonstrated. The proposed photodetector incorporates 5.28% Sn into the GeSn active layer, which redshifts the photodetection range to 2090 nm. In addition, the longer light–matter interaction length and good optical confinement of the proposed GeSn WGPD enhance the optical responses significantly. As a result, the proposed GeSn WGPD achieves a responsivity up to 0.52 A W−1 and a detectivity up to 7.9 × 108 cm Hz½ W−1 in the 2 μm wavelength band at room temperature. These promising results indicate that the developed GeSn WGPDs are promising candidates for integrated photonics in the 2 μm wavelength band.

Optical Design of a Common-Aperture Camera for Infrared Guided Polarization Imaging

Polarization and infrared imaging technology have unique advantages for various applications ranging from biology to ocean remote sensing. However, conventional combined polarization camera and infrared camera have limitations because they are constrained to single-band imaging systems with rotating polarizers and cascaded optics. Therefore, we propose a common-aperture mode based on multi-band infrared guided polarization imaging system (IGPIS) in this paper, which consists of infrared wide-area sensing and polarization features acquisition for accurate detection of ship targets. The IGPIS can provide images in visible polarization (0.45–0.76 μm), near-infrared polarization (0.76–0.9 μm), and long-wave infrared (8–12 μm) bands. Satellite attitude parameters and camera optical parameters are accurately calculated by establishing a dynamic imaging model for guidance imaging. We illustrate the imaging principle, sensors specifications and imaging performance analysis and the experimental results show that the MTF is 0.24 for visible and near-infrared, and 0.13 for long-wave infrared. The obtained multi-band images have an average gradient of 12.77 after accurate fusion. These results provide theoretical guidance for the design of common-aperture cameras in remote sensing imaging field.

High slope-efficiency quantum-dot lasers grown on planar exact silicon (001) with asymmetric waveguide structures

We report electrically pumped continuous-wave (CW) InAs/GaAs quantum dot lasers directly grown on planar exact silicon (001) with asymmetric waveguide structures. Surface hydrogen-annealing for the GaAs/ Si (001) templates and low-temperature growth for GaInP upper cladding layers were combined in the growth of the laser structure to achieve a high slope efficiency. For the broad-stripe edge-emitting lasers with 2-mm cavity length and 20-µm stripe width made from the above laser structure, a threshold current density of 203.5 A/cm2 and a single-facet slope efficiency of 0.158 W/A are achieved at ∼1.31 µm band under CW conditions. The extrapolated mean-time-to-failure reaches up to 21000 hours at room temperature, which is deduced from the data measured from C-mount packaged devices. Importantly, these results can provide a practical strategy to realize 1.3 µm wavelength band distributed feedback lasers directly on planar exact Si (001) templates with thin buffer layers.

Investigating the effects of surface moisture content on thermal infrared emissivity of urban underlying surfaces

As an inherent property of materials, emissivity critically reflects the material composition. Despite evidence on the positive correlation between surface moisture content (SMC) and the emissivity for soil, such correlations for other urban underlying surfaces have not been examined. Accordingly, this paper aimed to investigate the effects of SMC on the emissivity of ten representative urban underlying surfaces (including impervious and permeable ones), through comparisons of their emissivity spectra before and after water-sprinkling. Based on the spectra, the sliding-window algorithm was used to identify SMC-sensitive bands of the surfaces, whose increments of emissivity within the SMC-sensitive and 8.0 – 13.5 μm bands were analyzed. Furthermore, for soil, models characterizing the relationship between its SMC and emissivity were established. The results showed that the emissivity of most underlying surfaces increased with SMC, which was particularly evident in the SMC-sensitive bands (8.0 – 10.0 μm). Additionally, the impacts of SMC on emissivity (8.0 – 13.5 μm) depend on the properties of the surfaces. SMC critically influenced the emissivity (8.0 – 13.5 μm) of the concrete pavement, granite pavement, asphalt road and soil: their increment exceeded 0.02, which could lead to substantial fluctuations in retrieving temperature (0.9, 2.1, 1.0 and 2.3 K, respectively). However, SMC was found to exert little effect on the emissivity (8.0 – 13.5 μm) of the permeable brick pavement, gravel road, red clay brick pavement, grasses and shrubs. Lastly, variations in emissivity of the soil with SMC were optimally characterized by the sigmoidal model, whose correlation was the highest (adjusted-R2= 0.9848).

Metamaterial microbolometers for multi-spectral infrared polarization imaging

Vanadium oxide (VOx) microbolometers enable the construction of high-performance yet low-cost and uncooled imaging detectors in the mid-infrared spectrum. Typical micro-bolometers are broadband sensors with no polarization selectivity. Thus, imaging detectors based on microbolometers have to use separate spectral and polarization filters to select the target spectral bands and polarization states, and the resulting systems are complicated and bulky. Here we demonstrate that by using metamaterial absorbers (MAs), which are arrays of optical resonators with sub-wavelength dimensions and spacing, we simultaneously tailor the VOx microbolometers' spectral and polarization responses, the need for separate spectral filters and polarizers can be mitigated. The MAs selectively absorb the TM polarization component of the incident light in a spectral band with tunable central wavelength and bandwidth while rejecting the TE polarization component. Two MAs with average TM absorption of 0.8322 in the 5.150 µm - 6.422 µm band and 0.7720 in the 5.867 µm - 7.467 µm band are fabricated, and the polarization extinction ratio (PER) are 42.24 and 42.65, respectively. The MAs are applied to VOx micro-bolometers, and the measured detector responses agree well with the absorption spectra of the MAs. The achieved peak responsivities of two fabricated detectors are 1.0 V/W at 6.0 µm and 1.46 V/W at 6.8 µm, respectively. And the two detectors achieve a D* of 6.94×105 cm·Hz1/2W-1 at 11Hz and 9.95×105 cm·Hz1/2W-1 at 36Hz, respectively. Our work paved the way towards large format room temperature multi-spectral infrared polarization imaging detector.

Study on the optical and thermal properties of a new mid-infrared TeO2-Ta2O5-La2O3 glass

A new mid-infrared tellurite ternary glass with small glass formation area was prepared by modified melt quenching. A high-throughput, simple and fast glass melting process is realized by erecting the tube furnace sideways. The forming range of glass can be quickly and efficiently explored. Moreover, the equipment is convenient for stirring in the melting process, and can effectively reduce bubbles and stripes in the molten glass, thus preparing the matrix glass with excellent performance. The maximum phonon energy of the glass is 765 cm−1, and the appropriate phonon energy is beneficial to achieve intense mid-infrared luminescence or laser. The density of glass is 5.385 g/cm3, indicating high refractive index of this new glass. The glass transition temperature is 428 °C, and there is no obvious crystallization thermal effect before the glass melts. The thermal expansion coefficient of TeO2-Ta2O5-La2O3 (TTL) glass is 12.5 × 10−6K−1 (25–300 °C). The refractive index of glass is 2.01 and the Abbe number is 21.48. The maximum transmittance in the near infrared range is between 76.44% and 80.85%, while the theoretical transmittance is 80.08% (2700 nm). Therefore, this glass is a promising laser glass matrix material in the 2.0–2.7 μm band.

Mid-infrared Variability of Low-redshift Active Galactic Nuclei: Constraints on a Hot Dust Component with a Variable Covering Factor

Abstract We utilize mid-infrared multiepoch data from the Wide-field Infrared Survey Explorer over a ∼10 yr period in the W1 (3.4 μm) and W2 (4.6 μm) bands to investigate the structure of dusty torus in low-redshift (0.15 < z ≤ 0.4) active galactic nuclei (AGNs). We calculate a Spearman correlation coefficient (r 12) between the W1 magnitude and W1 − W2 color based on the light curve in individual objects. Interestingly, r 12 spans a broad range from −1 to 1 and is detected to be correlated with mean W1 − W2 color and AGN bolometric luminosity, in the sense that objects with a blue W1 − W2 color and low AGN luminosity tend to become redder (bluer) with increasing (decreasing) W1 brightness in the light curve (i.e., r 12 < 0), although the correlation of r 12 with the bolometric luminosity is relatively weak. The fit for the spectral energy distribution reveals a significant contribution from the host galaxy in the W1 and W2 bands. However, the dependencies of r 12 on the W1 − W2 color and AGN luminosity still persist even after careful elimination of the host light contribution. We propose that this result can be explained if the covering factor of the hot dust component decreases as the AGN luminosity increases.

Thermal Properties of 1847 WISE-observed Asteroids

Abstract We present new thermophysical model fits of 1847 asteroids, deriving thermal inertia, diameter, and Bond and visible geometric albedo. We use thermal flux measurements obtained by the Wide-field Infrared Survey Explorer (WISE) during its fully cryogenic phase, when both the 12 μm (W3) and 22 μm (W4) bands were available. We take shape models and spin information from the Database of Asteroid Models from Inversion Techniques (DAMIT) and derive new shape models through lightcurve inversion and combining WISE photometry with existing DAMIT lightcurves. When we limit our sample to the asteroids with the most reliable shape models and thermal flux measurements, we find broadly consistent thermal inertia relations with recent studies. We apply fits to the diameters D (km) and thermal inertia Γ (J m−2 s−0.5 K−1) normalized to 1 au with a linear relation of the form log [ Γ ] = α + β log [ D ] , where we find α = 2.667 ± 0.059 and β = −0.467 ± 0.044 for our sample alone and α = 2.509 ± 0.017 and β = −0.352 ± 0.012 when combined with other literature estimates. We find little evidence of any correlation between rotation period and thermal inertia, owing to the small number of slow rotators to consider in our sample. While the large uncertainties on the majority of our derived thermal inertia only allow us to identify broad trends between thermal inertia and other physical parameters, we can expect a significant increase in high-quality thermal flux measurements and asteroid shape models with upcoming infrared and wide-field surveys, enabling even more thermophysical modeling of higher precision in the future.

Shot-noise limited homodyne detection for MHz quantum light characterisation in the 2 µm band.

Characterising quantum states of light in the 2 µm band requires high-performance shot-noise limited detectors. Here, we present the characterisation of a homodyne detector that we use to observe vacuum shot-noise via homodyne measurement with a 2.07 µm pulsed mode-locked laser. The device is designed primarily for pulsed illumination. It has a 3-dB bandwidth of 13.2 MHz, total conversion efficiency of 57% at 2.07 µm, and a common-mode rejection ratio of 48 dB at 39.5 MHz. The detector begins to saturate at 1.8 mW with 9 dB of shot-noise clearance at 5 MHz. This demonstration enables the characterisation of megahertz-quantum optical behaviour in the 2 µm band and provides a guide of how to design a 2 µm homodyne detector for quantum applications.

Ultrafast ytterbium-doped all-fiber laser with vortex pulse emissions

Ultrafast vortex pulses emitted at 1 μm band are highly sought after in many fields, here we propose an all-fiber laser for achieving that. The designed laser is switchable to emit ultrafast orbital angular momentum (OAM) and cylindrical vector beams. The beam purities are calculated to be higher than 94%. Moreover, the as-designed laser can achieve ultrafast pulse with a duration of 10.4 ps and maximum energy of 619.3 pJ. Generally, it is the shortest width and largest energy of OAM emission in ultrafast ytterbium-doped all-fiber laser so far.

A Maritime Cloud-Detection Method Using Visible and Near-Infrared Bands over the Yellow Sea and Bohai Sea

Accurate cloud-masking procedures to distinguish cloud-free pixels from cloudy pixels are essential for optical satellite remote sensing. Many studies on satellite-based cloud-detection have been performed using the spectral characteristics of clouds in terms of reflectance and temperature. This study proposes a cloud-detection method using reflectance in four bands: 0.56 μm, 0.86 μm, 1.38 μm, and 1.61 μm. Methodologically, we present a conversion relationship between the normalized difference water index (NDWI) and the green band in the visible spectrum for thick cloud detection using moderate-resolution imaging spectroradiometer (MODIS) observations. NDWI consists of reflectance at the 0.56 and 0.86 μm bands. For thin cloud detection, the 1.38 and 1.61 μm bands were applied with empirically determined threshold values. Case study analyses for the four seasons from 2000 to 2019 were performed for the sea surface area of the Yellow Sea and Bohai Sea. In the case studies, the comparison of the proposed cloud-detection method with the MODIS cloud mask (CM) and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation data indicated a probability of detection of 0.933, a false-alarm ratio of 0.086, and a Heidke Skill Score of 0.753. Our method demonstrated an additional important benefit in distinguishing clouds from sea ice or yellow dust, compared to the MODIS CM products, which usually misidentify the latter as clouds. Consequently, our cloud-detection method could be applied to a variety of low-orbit and geostationary satellites with 0.56, 0.86, 1.38, and 1.61 μm bands.

Optical parametric generation in OP-GaAs waveguides pumped by a femtosecond fluoride fiber laser.

We report on mid-infrared optical parametric generation in the 4-5 μm and 9-12 μm bands by pumping custom-designed orientation-patterned gallium arsenide (OP-GaAs) rib waveguides with an ultrafast femtosecond fiber laser system. This pump source is seeded by a mode-locked fluoride fiber laser with 59 MHz repetition rate and can be tuned between 2.8 and 3.2 μm using a soliton self-frequency shifting stage. The single TE and TM modes OP-GaAs crystals feature quasi-phase-matched grating periods of 85 and 90 μm and different transverse sizes thus allowing a wide spectral tunability.