Exploiting spatio-spectral aberrations for rapid synchrotron infrared imaging.

High-quality infrared focal plane arrays (FPAs) are used in many satellite, astronomical, and terrestrial applications. These applications require highly-sensitive, low-noise FPAs, and therefore do not benefit from advances made in low-cost thermal imagers where reducing cost and enabling high-temperature operation drive device development. Infrared detectors used in FPAs have been made for decades from alloys of mercury cadmium telluride (MCT). These infrared detectors are nearing the believed limit of their performance. This limit, known in the infrared detector community as Rule 07, dictates the dark current floor for MCT detectors, in their traditional architecture, for a given temperature and cutoff wavelength. To overcome the bounds imposed by Rule 07, many groups are working on detector compounds other than MCT. We focus on detectors employing III-V-based gallium-free In As Sb superlattice active regions while also changing the basic architecture of the pixel to improve signal-to-noise. Our architecture relies on a resonant, metallic, subwavelength nanoantenna patterned on the absorber surface, in combination with a Fabry-Perot cavity, to couple the incoming radiation into tightly confined modes near the nanoantenna. This confinement of the incident energy in a thin layer allows us to greatly reduce the volume of the absorbing layer to a fraction of the free-space wavelength, yielding a corresponding reduction in dark current from spontaneously generated electron-hole pairs in the absorber material. This architecture is detector material agnostic and could be applied to MCT detector structures as well, although we focus on using superlattice antimonide-based detector materials. This detector concept has been applied to both mid-wave (3–5 μm) and longwave (8–12 μm) infrared detectors and absorbers. Here we examine long-wave devices, as these detectors currently have a larger gap between desired device performance and that of currently existing detectors. The measured structures show an external quantum efficiency exceeding 50%. We present a comparison of the modeled and measured photoresponse of these detectors and compare these detectors to currently available commercial detectors using relevant metrics such as external quantum efficiency. We also discuss modeling of crosstalk between adjacent pixels and its influence on the potential for a dual-wavelength detector. Finally, we evaluate potential advances in these detectors that may occur in the near future.

: This report summarizes experiments carried out at Rome Laboratory (RL) under a Laboratory Director Funds (LDF) effort. Experiments were carried out at both SCITEC and RL in conjunction with the Intelligence and Reconnaissance Directorate and the Photonics Center. Experimental results are described regarding the sensitivity and noise characteristics of commercially available mercury cadmium telluride (MCT) detectors and preamps. Also presented are some measurements of potential ways to reject false alarms. Intelligence and Reconnaissance, mercury cadmium telluride (MCT).

The Japanese Aerospace Exploration Agency (JAXA) will be conducting the Global Change Observation Mission (GCOM) for monitoring of global environmental change. SGLI (Second Generation Global Imager) is an optical sensor on board GCOM-C (Climate), that includes a Long Wave IR Detector (LWIRD) sensitive up to about 13 μm. SGLI will provide high accuracy measurements of the atmosphere (aerosol, cloud ...), the cryosphere (glaciers, snow, sea ice ...), the biomass and the Earth temperature (sea and land). Sofradir is a major supplier of Space industry based on the use of a Space qualified MCT technology for detectors from 0.8 to 15 μm. This mature and reproducible technology has been used for 15 years to produce thousands of LWIR detectors with cut-off wavelengths between 9 and 12 μm. NEC Toshiba Space, prime contractor for the Second Generation Global Imager (SGLI), has selected SOFRADIR for its heritage in space projects and Mercury Cadmium Telluride (MCT) detectors to develop the LWIR detector. This detector includes two detection circuits for detection at 10.8 μm and 12.0 μm, hybridized on a single CMOS readout circuit. Each detection circuit is made of 20x2 square pixels of 140 μm. In order to optimize the overall performance, each pixel is made of 5x5 square sub-pixels of 28 μm and the readout circuit enables sub-pixel deselection. The MCT material and the photovoltaic technology are adapted to maximize response for the requested bandwidths: cut-off wavelengths of the 2 detection circuits are 12.6 and 13.4 μm at 55K. This detector is packaged into a sealed housing for full integration into a Dewar at 55K. This paper describes the main technical requirements, the design features of this detector, including trade-offs regarding performance optimization, and presents preliminary electro-optical results.

: The decomposition of GD on alumina supported CeO2 was determined at 25 degrees C in a quasi micro-reactor. One microliter of GD solution (50% by weight in carbon tetrachioride) was injected into a CeO2/alumina (-40 mg) packed inlet tube of a Perkin Elmer Auto M Gas Chromatograph and maintained at 30 degrees C. A Nicolet 800 Bench Spectrometer with a mercury cadmium-telluride detector (11,700 to 600 /cm) was used to monitor the effluent. An injection was made approximately every hour until GD was detected. The adsorbent was then extracted with acetonitrile and the solution treated with BSTFA to esterify any hydrolysate; the mixture was assayed by GC/MS. The GD (521 micromol/g) was decomposed on CeO2/alumina; the major products were pinacolyl methylphosphonic acid, methyl phosphonic acid, and dipinacolyl methylphosphonate. The decomposition of GD on alumina supported CeO2 was determined at 25 degrees C in a quasi micro-reactor. One microliter of GD solution (50% by weight in carbon tetrachioride) was injected into a CeO2/alumina % 40 mg) packed inlet tube of a Perkin Elmer Auto M Gas Chromatograph and maintained at 30 degrees C. A Nicolet 800 Bench Spectrometer with a mercury cadmium-telluride detector (11,700 to 600 cm(exp -1) was used to monitor the effluent. An injection was made approximately every hour until GD was detected. The adsorbent was then extracted with acetonitrile and the solution treated with BSTFA to esterify any hydrolysate; the mixture was assayed by GC/MS. The GD (521 umo1/g) was decomposed on CeO2/alumina; the major products were pinacolyl methylphosphonic acid, methyl phosphonic acid, and dipinacolyl methylphosphonate.

A method for the direct determination of carbon dioxide in aqueous solutions using a room-temperature mid-infrared (MIR) quantum cascade laser at 2330 cm(-1) is reported. The absorption values of different carbon dioxide concentrations were measured in a 119 microm CaF2 flow-through cell. An optical system made of parabolic mirrors was used to probe the flow cell and to focus the laser beam on the mercury cadmium telluride (MCT) detector. Aqueous carbon dioxide standards were prepared by feeding different mixtures of gaseous N2 and CO2 through wash bottles at controlled temperature. The concentration of the dissolved CO2 was calculated according to Henry's law, taking into account the temperature and the partial pressure of CO2. The carbon dioxide standards were connected via a selection valve to a peristaltic pump for subsequent, automated measurement in the flow-through cell. A calibration curve was obtained in the range of 0.338 to 1.350 g/L CO2 with a standard deviation of the method sxo equal to 19.4 mg/L CO2. The limit of detection was calculated as three times the baseline noise over time and was determined to be 39 mg/L.

We describe development of spectrally tunable micro-engineered filters operating in the longwave infrared (LWIR) from 8 to 12 micron based on the guided mode resonance (GMR) phenomenon. The device structure consists of a subwavelength dielectric grating on top of a planar waveguide using high index dielectric transparent materials, i.e., germanium (Ge) with a refractive index of 4.0 and zinc selenide (ZnSe) with refractive index of 2.4. The filters are designed to reflect incident broadband light at one (or more) narrow spectral band while fully transmitting the other wavelengths. Tuning of the reflection wavelength is achieved by changing the angle of incidence of light by mechanically tilting the filter. Filters based on one dimensional (1-D) gratings are polarization dependent and those based on two dimensional (2-D) gratings are less sensitive to incident polarization of light. Both filters were fabricated using standard dielectric deposition and photolithographic techniques and characterized. Simple 2-layer anti-reflection coatings were applied to improve transmission over the entire spectral region. Our experimental setup consists of a modified commercial Fourier Transform Infrared Spectrometer (FTIR) system with a separate chamber for a collimated incident beam of light, focusing optics, a liquid-nitrogen-cooled mercury cadmium telluride (MCT) detector, a wire grid polarizer and a micro-engineered filter. We will present detailed characterization experiment and compare the theoretical and experimental results.

Direct determination of tagitinin C in Tithonia diversifolia leaves by on-line coupling of supercritical carbon dioxide extraction to FT-IR spectroscopy by means of optical fibres

This paper reports the open path measurement of atmospheric transmission in the spectral region of 3000–3450 nm using a mid infrared tunable lidar in New Delhi (28.7oN, 77.1oE), India. Results on the measurement of atmospheric transmission in New Delhi are reported for the first time, to the best of our knowledge. A tunable infrared lidar system has been developed in-house, which transmits laser radiation with the wavelength interval of 1 nm in the above spectral band into the atmosphere. A 200-mm-diameter Cassegrain receiver telescope with mercury cadmium telluride (MCT) detector is used to collect the backscattered radiation from the atmosphere. The reflected laser radiation received from the tower located at a distance of 400 m is used to generate the transmission spectrum. Data recorded during the daytime measurements have been considered in this paper. Transmission spectra measured over several days showed a similar pattern, which confirmed the repeatability of the system performance. The measured spectra are also compared with the SkyCalc transmission model generated using the online database. Preliminary analysis indicated that these spectra had good agreement in general with a small shift in wavelength region. We have also analyzed the HITRAN database line-by-line and identified the possible major absorbing molecules in this band. The sources of air pollutants that absorb in this band and also discussed.

From the rats treated with stable gastric pentadecapeptide BPC 157 (10ng/kg ip) or saline (5ml/kg ip) at 5 min before sacrifice, the spectra of thoracic aorta tissue samples were compared. From each rat, 20 samples were cut and FTIR spectra were recorded.Vibrational spectra of the samples were recorded with a Perkin‐Elmer Spectrum GX spectrometer equipped with liquid N2 refrigerated Mercury Cadmium Telluride (MCT) detector. Data were acquired in 450 ‐ 4000 cm‐1 spectral range, in transmission mode with a resolution of 4 cm‐1.First, all recorded spectra were baseline corrected and normalized. Then we utilized the principal component analysis (PCA) to examine the possibility of separating BPC treated and control samples on a PCA score‐score graph. Using 100 spectra of BPC treated and 100 spectra of control samples, a PCA model was made. As seen in Figure 1, there is a clear distinction, mostly due to the PC1 score, between spectra of BPC treated (red) from the control group (green).To identify the parts of FTIR spectra that contributed the most to the separation between BPC treated and the control group of spectra differential spectrum was calculated and compared with PC1 loadings.Differential spectrum and PC loadings show that main bands responsible for separation of the BPC treated and control sample spectra are in the range from 930‐1200 cm‐1, then vibrational bands at 1660 cm‐1,1730 cm‐1, 1120 cm‐1 and in the range from 2840 – 3090 cm‐1. In the first range, there are three vibrational bands at 968 cm‐1, 1087 cm‐1 and 1240 cm‐1 that belong to P‐O symmetric and asymmetric vibrations in nucleic acids respectably, and vibrational band 1170 cm‐1 that belongs to C‐O and C‐O‐C stretching vibrations of carbohydrate. The vibrational band at 1660cm‐1 belongs to amid I stretching vibrations of proteins, and the last range of spectral lines belongs to C‐H symmetric and asymmetric C‐H, C‐H2 and C‐H3 vibrations in lipids. The line at 1730 cm‐1 that is very pronounced in control group spectra is C‐O symmetric vibration in fatty acids. Most prominent difference between BPC treated and control group was observed region of C‐H vibrations of lipids and vibrational line at 1730 cm‐1 of fatty acids.Thus, different FTIR spectra evidenced that BPC treatment causes changes of the tissue at molecular level.

A new infrared radiation thermometer having a high temporal response and a high spatial resolution is being developed at NMIJ to meet the existing demand for measurements of thermophysical properties of thin films, coatings, and solids in microscale. The thermometer consists of a photovoltaic (pv)-type of mercury cadmium telluride (MCT) detector and a compact Cassegrain type of mirror optics without a mechanical chopper. The performance of the thermometer has been well characterized experimentally. Sensing infrared radiation around 10 μm of wavelength, the thermometer covers the temperature range from −50 to 150°C and has a temperature resolution better than 0.3°C at −50°C for blackbody radiators. The spatial resolution has also been checked by using a test pattern (USAF 1951) for rating the resolution of optical systems. Temperature changes of specimen surfaces in periodic heating with a laser beam modulated above 100 kHz have been observed successfully with the thermometer. The results shows that the thermometer has great potential for measuring the thermal diffusivity, thermal conductivity, and specific heat capacity of microscale substances at low temperatures based on the periodic heating and pulsed laser heating methods.

A gas sensing method based on quartz-tuning-fork enhanced photothermal spectroscopy (QEPTS) is reported in this paper. Unlike usually used thermally sensitive elements, a sharply resonant quartz-tuning-fork with the capability of enhanced mechanical resonance was used to amplify the photothermal signal level. Acetylene (C2H2) detection was used to verify the QEPTS sensor performance. The measured results indicate a minimum detection limit (MDL) of 718 ppb and a normalized noise equivalent absorption coefficient (NNEA) of 7.63 × 10-9 cm-1W/√Hz. This performance demonstrates that QEPTS can be an ultra-high sensitive technique for gas detection and shows superiority when compared to usually used methods of tunable diode laser absorption spectroscopy (TDLAS) and quartz-enhanced photoacoustic spectroscopy (QEPAS). Furthermore, when compared to an optical detector, especially a costly mercury cadmium telluride (MCT) detector with cryogenic cooling used in TDLAS, a quartz-tuning-fork is much cheap and tiny. Besides, compared to the QEPAS technique, QEPTS is a non-contact measurement technique and therefore can be used for standoff and remote trace gas detection.

The Application of Reflection Infrared and Surface Enhanced Raman Spectroscopy to the Characterization of Chemisorbed Organic Disulfides on Au

A new type of vacuum blackbody containing both a blackbody cavity and a solid material sample was fabricated using a cryogenic refrigerator. It was to construct a highly sensitive infrared spectral-radiation measurement system using a programmable temperature control device, a Fourier transform infrared spectrophotometer, and two mercury-cadmium-telluride (MCT) detectors. Evaluation showed that the temperature of the blackbody cavity wall was accurately set within ±0.2 K for 173 to 373 K and that the nonlinearity of the system response output at 173 to 373 K was within 0.8% with the proper use of the two MCT detectors. An emissivity comparison experiment using black paint (No. 1) showed that the proposed blackbody cavity method had a coincidence within 0.015 of a diffuse reflectance measuring method at 5 to 11.6 μm. For ceramics, the emissivity temperature dependence for alumina and zirconia at 273 to 373 K was within ±0.06 and ±0.04, respectively.

The long-wave infrared (LWIR) band holds critical value in applications such as industrial monitoring, biomedical imaging, and spectral analysis. However, frequency conversion for wavelengths above 5 μm, which covers the core LWIR spectral range, remains challenging due to the limited effective nonlinear coefficients of most optical crystals and severe absorption losses in the mid-infrared to LWIR region, restricting the efficiency of upconversion processes. Meanwhile, mainstream commercial mercury cadmium telluride (HgCdTe) detectors typically require cryogenic operation to achieve high signal-to-noise ratios (SNRs), coupled with high fabrication costs, which severely hinders their widespread deployment under room-temperature conditions. This paper presents a room-temperature LWIR detection device based on frequency upconversion technology, which enables high-sensitivity detection across a broad spectral range (7.5-9 μm) without the need for cooling. Experimental results demonstrate that the system achieves a minimum detectable energy at the fJ level under nanosecond-pulse operation, along with excellent wavelength stability and high responsivity. Compared with typical commercial HgCdTe detectors, the proposed device exhibits a sensitivity improvement of up to approximately 2.4 orders of magnitude at room temperature, significantly enhancing detection accuracy and signal-to-noise ratio for LWIR signals under room temperature conditions. This work provides an effective technical pathway toward the development of room-temperature, low-cost, and high-performance LWIR detection systems, showing promising potential for applications in real-time monitoring, portable sensing, and spectroscopic analysis.

: Infrared (IR) sensor technology is critical to all phases of ballistic missile defenses. Traditionally, material systems such as indium antimonide (InSb), platinum silicide (PtSi), mercury cadmium telluride (MCT), and arsenic doped silicon (Si: As) have dominated IR detection. Improvement in surveillance sensors and interceptor seekers requires large size, highly uniform and multicolor (or multispectral) IR focal plane arrays involving mid-wave, long-wave and very-long-wave IR regions. Among the competing technologies are the quantum well infrared photodetectors (QWIP) based on lattice matched GaAs/Al GaAs and strained layer InGaAs/AlGaAs material systems. In this paper, a discussion of cooled IR technology with emphasis on QWIP and MCT will be given. Details will be given concerning device physics, material growth, device fabrication, device performance, and cost effectiveness for long wavelength infrared, very long wavelength infrared, and multicolor applications. The conclusion drawn here is that even though QWIP cannot compete with MCT at the single device level, it has potential advantages over MCT for long wavelength and very long wavelength focal plane array applications in term of the array size, uniformity, operability, yield, reliability, and cost of the systems. QWIPs are especially promising for very-long-wave IR at low temperature operation, and when simultaneous multicolor detection using a single focal plane array is desired. Operating a very-long-wave IR focal plane array at low background is a big challenge to both MCT and QWIP, while QWIP has more potential to be realized due to its good device property at low temperature.