Differential confocal technology based on radial birefringent pupil filtering principle

In order to improve the spatial resolution of a confocal system, a radial birefringent pupil filter (RBPF) is introduced into a differential confocal system. RBPF consists of two polarizers with a birefringent element between them, and its pupil function is deduced from Jones matrix. The thickness and curvature radius of RBPF are optimized independently, using the first zero coordinate ratio. The pupil function is modulated by RBPF to enhance the half-width of the response function, and lateral resolution is improved when response curve is changed with the position of RBPF as well as the polarization; then axial super-resolution of the system can be guaranteed using differential confocal detection mechanism. In comparison with conventional pupil filtering technology, RBPF features high lateral resolution and can be easily produced; moreover, it also has a simple structure. Together with its low cost, RBPF provides a new way for the improvement of super-resolution of confocal system. It is indicated from theoretical analysis and preliminary experiments that the lateral resolution can be significantly improved and the measurement error is reduced by 76 nm when measuring a standard grating of period 3 μm; the axial resolution up to 3 nm has been achieved using the optimized pupil filter. In addition to its application for measurement of a small irregular surface in a limited space, the whole differential confocal system proposed can be fitted onto a coordinate measuring machine for non-contact measurement of dimensions and surface roughness.     

Displacement measurement system for inverters using computer micro-vision

We propose a practical system for noncontact displacement measurement of inverters using computer micro-vision at the sub-micron scale. The measuring method of the proposed system is based on a fast template matching algorithm with an optical microscopy. A laser interferometer measurement (LIM) system is built up for comparison. Experimental results demonstrate that the proposed system can achieve the same performance as the LIM system but shows a higher operability and stability. The measuring accuracy is 0.283 μm.     

A thin film magnetic field sensor of sub-pT resolution and magnetocardiogram (MCG) measurement at room temperature

We developed a very sensitive high-frequency carrier-type thin film sensor with a sub-pT resolution using a transmission line. The sensor element consists of Cu conductor with a meander pattern (20 mm in length, 0.8 mm in width, and 18 μm in thickness), a ground plane, and amorphous CoNbZr film (4 μm in thickness). The amplitude modulation technique was employed to enhance the magnetic field resolution for measurement of the high-frequency field (499 kHz), a resolution of 7.10×10^?13 T/Hz^1/2 being achieved, when we applied an AC magnetic field at 499 kHz. The phase detection technique was applied for measurement of the low frequency field (around 1 Hz). A small phase change was detected using a dual mixer time difference method. A high phase change of 130°/Oe was observed. A magnetic field resolution of 1.35×10^?12 T/Hz^1/2 was obtained when a small AC field at 1 Hz was applied. We applied the sensor for magnetocardiogram (MCG) measurement using the phase detection technique. We succeeded in measuring the MCG signal including typical QRS and T waves, and compared the MCG with a simultaneously obtained conventional electrocardiogram (ECG) signal.     

Resonant detectors and focal plane arrays for infrared detection

We are developing resonator-QWIPs for narrowband and broadband long wavelength infrared detection. Detector pixels with 25 μm and 30 μm pitches were hybridized to fanout circuits and readout integrated electronics for radiometric measurements. With a low to moderate doping of 0.2–0.5 × 10¹⁸ cm⁻³ and a thin active layer thickness of 0.6–1.3 μm, we achieved a quantum efficiency between 25 and 37% and a conversion efficiency between of 15 and 20%. The temperature at which photocurrent equals dark current is about 65 K under F/2 optics for a cutoff wavelength up to 11 μm. The NEΔT of the FPAs is estimated to be 20 mK at 2 ms integration time and 60 K operating temperature. This good performance confirms the advantages of the resonator-QWIP approach.     

A design study of a triple field of view 8–12 μm waveband airborne FLIR

In this work, a design study of a three field-of-view (FOV) optical system for 8–12 μm imaging using a 288×4 focal plane array detector is presented. The detector pixel size is 25 μm×28 μm. The f/# of the detector is 1.76. In order to switch the FOVs, three different optical configurations are superimposed and all three configurations are optimized. The narrow and medium FOV switching is based on movement of the second negative lens of the afocal system, whereas the wide FOV is selected by inserting a mirror between the 4th and 5th lenses of the afocal system. By inserting a switching mirror, the objective part of the first configuration is blocked out; nevertheless the afocal of the wide FOV is activated. The imager part of the layout is common for all FOVs. Diffractive and aspheric surfaces are utilized to control chromatic and all other kinds of aberrations, reducing the total lens number. The final optical designs, together with their modulation transfer function (MTF) plots, are illustrated, exhibiting excellent performance in all three FOVs. More specifically, the paper emphasizes how the displacement of compensating lenses effect the MTF of the system and how automatic movements of the lenses are used to eliminate the defocusing problem under changing environmental conditions.     

Demonstration of a portable near-infrared CH4 detection sensor based on tunable diode laser absorption spectroscopy

A portable near-infrared (NIR) CH₄ detection sensor based on a distributed feedback (DFB) laser modulated at 1.654 μm is experimentally demonstrated. Intelligent temperature controller with an accuracy of −0.07 to +0.09 °C as well as a scan and modulation module generating saw-wave and cosine-wave signals are developed to drive the DFB laser, and a cost effective lock-in amplifier used to extract the second harmonic signal is integrated. Thorough experiments are carried out to obtain detection performances, including detection range, accuracy, stability and the minimum detection limit (MDL). Measurement results show that the absolute detection error relative to the standard value is less than 7% within the range of 0–100%, and the MDL is estimated to be about 11 ppm under an absorption length of 0.2 m and a noise level of 2 mV_pp. Twenty-four hours monitoring on two gas samples (0.1% and 20%) indicates that the absolute errors are less than 7% and 2.5%, respectively, suggesting good long term stability. The sensor reveals competitive characteristics compared with other reported portable or handheld sensors. The developed sensor can also be used for the detection of other gases by adopting other DFB lasers with different center-wavelength using the same hardware and slightly modified software.     

10.6 μm Infrared light photoinduced insulator-to-metal transition in vanadium dioxide

Vanadium dioxide has excellent phase transition characteristic. Before or after phase transition, its optical, electrical, magnetic characteristic hangs hugely. It has a wide application prospect in many areas. Now, the light which can make vanadium dioxide come to pass photoinduced phase transition range from soft X-ray to medium infrared light (6.9 μm, 180 meV). However, whether 10.6 μm (117 meV) long wave infrared light can make vanadium dioxide generate photoinduced phase transition has been not studied. In this paper, we researched the response characteristic of vanadium dioxide excited by 10.6 μm infrared light. We prepared the vanadium dioxide and test the changes of vanadium dioxide thin film’s transmittance to 632.8 nm infrared light when the thin film is irradiate by CO₂ laser. We also test the resistivity of vanadium dioxide. Excluding the effect of thermal induced phase transition, we find that the transmittance of vanadium dioxide thin film to 632.8 nm light and resistivity both changes when irradiating by 10.6 μm laser. This indicates that 10.6 μm infrared light can make the vanadium dioxide come to pass photoinduced phase transition. The finding makes vanadium has a potential application in recording the long-wave infrared hologram and making infrared detector with high resolution.     

A new subdivision method for grating-based displacement sensor using imaging array

A new subdivision method for grating-based displacement sensor was proposed in the present study, which takes advantages of imaging array's high resolution and pixels’ good uniformity in the space. In this method, the magnified grating image is received by imaging array and grating pitch is directly subdivided by pixels, which is quite different from that moiré fringe is subdivided by complex subsequent circuits in moiré-type displacement sensor. The displacement is statistically calculated by using the whole grating image, which greatly eliminates the errors arising from illumination, electrical signals’ fluctuation, grating defect, and so on. Therefore, the subdivision method is easy to obtain signal with high signal-to-noise ratio, insensitive to some external factors, and able to attain high measurement precision with low cost. In this paper, the principle of subdivision method was illuminated, the systemic resolution was theoretically discussed, the measurement precision was experimentally checked, and the uncertainty of measurement was analyzed. The subdivision system consisted of the grating with 20-μm pitch and the CMOS image sensor with the pixels of 1280×1024 had the resolution of 0.04 μm, and the maximum displacement error was less than 0.4 μm, which has been tested in the Abbe comparator platform.     

Application of robust color composite fringe in flip-chip solder bump 3-D measurement

This study developed a 3-D measurement system based on flip-chip solder bump, used fringes with different modulation intensities in color channels, in order to produce color composite fringe with robustness, and proposed a multi-channel composite phase unwrapping algorithm, which uses fringe modulation weights of different channels to recombine the phase information for better measurement accuracy and stability. The experimental results showed that the average measurement accuracy is 0.43μm and the standard deviation is 1.38 µm. The results thus proved that the proposed 3-D measurement system is effective in measuring a plane with a height of 50 μm. In the flip-chip solder bump measuring experiment, different fringe modulation configurations were tested to overcome the problem of reflective coefficient between the flip-chip base board and the solder bump. The proposed system has a good measurement results and robust stability in the solder bump measurement, and can be used for the measurement of 3-D information for micron flip-chip solder bump application.     

High resolution scanning microanalysis on material surfaces using UV femtosecond laser induced breakdown spectroscopy

Femtosecond lasers together with high resolution optics have given us the ability to achieve submicron ablation spots which can play an important role in specific micromachining applications. Light emitted from the plasma at the sample surface created by a focused femtosecond laser pulse can also be used in laser induced breakdown spectroscopy (LIBS) and allows us to characterize the chemical composition of the target surface with micron-level lateral resolution. The spatial resolution using LIBS has often been defined by measuring the FWHM of the crater size. In this report, we study the application of femtosecond 266 nm laser pulses with very low energies of 10׳s of nanojoules. We have investigated spatial resolution using the detection of thin strips of chromium on silicon substrates and compared the actual width of the chromium versus the experimentally obtained width using LIBS detection. The variation of signal levels for low pulse energies is investigated on chromium surfaces. A spatial resolution of ~1 μm was obtained for detection of chromium from the emission.     

Three-dimensional space charge cartographies by FLIMM in electron irradiated polymers

High resolution three-dimensional space charge cartographies obtained on 50 μm PTFE samples by using FLIMM technique are presented in this article. Samples were irradiated by a 30 keV electron beam. Charges were injected according to the grid pattern put on the sample during irradiation. A new measurement strategy associated with a new set-up leads to an improvement in measurements accuracy and precision. With this new strategy, measurements were performed rapidly, at a chosen depth and with a low lateral resolution in order to map the space charge profile in the whole sample and to choose a study area. After selecting an interesting area, space charge cartographies were carried out with a very high lateral resolution of about 1 μm. The irradiated zones according to the grid pattern were well reconstructed and the injection depth did not exceed 4 μm.     

Absolute line intensities measurements and calculations for the 5.7 and 3.6 μm bands of formaldehyde

The goal of this study is to achieve absolute line intensities for the strong 5.7 and 3.6 μm bands of formaldehyde and to generate, for both spectral regions, an accurate list of line positions and intensities. Both bands are now used for the infrared measurements of this molecule in the atmosphere. However, in the common access spectroscopic databases there exists, up to now, no line parameters for the 5.7 μm region, while, at 3.6 μm, the quality of the line parameters is quite unsatisfactory. High-resolution Fourier transform spectra were recorded for the whole 1600–3200 cm^?1 spectral range and for different path-length-pressure products conditions. Using these spectra, a large set of H₂CO individual line intensities was measured simultaneously in both the 5.7 and 3.6 μm spectral regions. From this set of experimental line strength which involve, at 5.7 μm the ν₂ band and, at 3.6 μm, the ν₁ and ν₅ bands together with nine dark bands, it has been possible to derive a consistent set of line intensity parameters for both the 5.7 and 3.6 μm spectral regions. These parameters were used to generate a line list in both regions. For this task, we used the line positions generated in [Margulés L, Perrin A, Janeckovà R, Bailleux S, Endres CP, Giesen TF, et al. Can J Phys, accepted] and [Perrin A, Valentin A, Daumont L, J Mol Struct 2006;780–782:28–42] for the 5.7 and 3.6 μm, respectively. The calculated band intensities derived for the 5.7 and 3.6 μm bands are in excellent agreement with the values achieved recently by medium resolution band intensity measurements. It has to be mentioned that intensities in the 3.6 μm achieved in this work are on the average about 28% stronger than those quoted in the HITRAN or GEISA databases. Finally, at 3.6 μm the quality of the intensities was significantly improved even on the relative scale, as compared to our previous study performed in 2006.     

Influence of the p-type doping on the radiometric performances of MWIR InAs/GaSb superlattice photodiodes

In this paper, quantum efficiency (QE) measurements performed on type-II InAs/GaSb superlattice (T2SL) photodiodes operating in the mid-wavelength infrared domain, are reported. Several comparisons were made in order to determine the SL structure showing optimum radiometric performances: same InAs-rich SL structure with different active zone thicknesses (from 0.5 μm to 4 μm) and different active zone doping (n-type versus p-type), same 1 μm thick p-type active zone doping with different SL designs (InAs-rich versus GaSb-rich and symmetric SL structures). Best result was obtained for the p-type doped InAs-rich SL photodiode, with a 4 μm active zone thickness, showing a QE that reaches 61% at λ = 2 μm and 0 V bias voltage.     

Dimensional characterization of opaque samples with a ring interferometer

In the present work, we introduce an optical method to characterize opaque samples. The technique combines low coherence interferometry with a ring configuration. This set-up, let us to obtain the thickness of the sample and the topography of both faces simultaneously by measuring the optical path difference with a reference arm. Experimental results in metal gauge blocks up to 1 mm are shown. A resolution better than 5 μm was obtained.     

320 × 256 Short-/Mid-Wavelength dual-color infrared focal plane arrays based on Type-II InAs/GaSb superlattice

Short-/Mid-Wavelength dual-color infrared focal plane arrays based on Type-II InAs/GaSb superlattice are demonstrated on GaSb substrate. The material is grown with 50% cut-off wavelength of 2.9 μm and 5.1 μm for the blue channel and red channel, separately at 77 K. 320 × 256 focal plane arrays fabricated in this wafer is characterized. The peak quantum efficiency without antireflective coating is 37% at 1.7 μm under no bias voltage and 28% at 3.2 μm under bias voltage of 130 mV. The peak specific detectivity are 1.51 × 10¹² cm·Hz^1/2/W at 2.5 μm and 6.11x10¹¹ cm·Hz^1/2/W at 3.2 μm. At 77 K, the noise equivalent difference temperature presents average values of 107 mK and 487 mK for the blue channel and red channel separately.     

Bias-selectable mid-/long-wave dual band infrared focal plane array based on Type-II InAs/GaSb superlattice

In this paper, a mid-/long-wave dual-band detector which combined PπMN structure and unipolar barrier was developed based on type-II InAs/GaSb superlattice. A relevant 320 × 256 focal plane array (FPA) was fabricated. Unipolar barrier and PπMN structure in our dual band detector structure were used to suppress cross-talk and dark current, respectively. The two channels, with respective 50% cut-off wavelength at 4.5 μm and 10 μm were obtained. The peak quantum efficiency (QE) of mid wavelength infrared (MWIR) band and long wavelength infrared (LWIR) band are 53% at 3.2 μm under no bias voltage and 40% at 6.4 μm under bias voltage of −170 mV, respectively. And the dark current density under 0 and −170 mV of applied bias are 1.076 × 10⁻⁵ A/cm² and 2.16 × 10⁻⁴ A/cm². The specific detectivity of MWIR band and LWIR band are 2.15 × 10¹² cm·Hz^1/2/W at 3.2 μm and 2.31 × 10¹⁰ cm·Hz^1/2/W at 6.4 μm, respectively, at 77 K. The specific detectivity of LWIR band maintains above 10¹⁰ cm·Hz^1/2/W at the wavelength range from 4.3 μm to 10.2 μm under −170 mV. The cross-talk, selectivity parameter at 3.0 μm, about 0.14 was achieved under bias of −170 mV. Finally, the thermal images were taken by the fabricated FPA at 77 K.     

Experimental investigation on charging characteristics and penetration efficiency of PM2.5 emitted from coal combustion enhanced by positive corona pulsed ESP

The electrostatic precipitator (ESP) has been extensively used for collecting aerosol particles emitted from coal combustion, but its collection efficiency of PM2.5 (Particulate matter whose aerodynamic diameter is less than 2.5 μm) is relatively low due to insufficient particle charging. The positive pulsed ESP is considered to enhance particle charging and improve collection efficiency. A laboratory-scale pulsed ESP with wire-plate electrode configuration was established to investigate the particle charging and penetration efficiency under controlled operating conditions of different applied impulse peak voltages, impulse frequencies, dust loadings and residence times. The results show that most particles larger than 0.2 μm are negatively charged, while most particles smaller than 0.2 μm are positively charged. For a given operating condition, the particle penetration efficiency curve has the highest penetration efficiency for particles with a diameter near 0.2 μm, and there is always a negative correlation between the particle penetration efficiency and the average number of charges per particle. Under the same operating conditions, the particle penetration efficiency decreases with increasing impulse peak voltage and impulse frequency, but increases as the dust loading increases. The results imply that residence time of 4 s is optimum for particle charging and collection. PM2.5 number reduction exceeding 90% was achieved in our pulsed ESP.     

Evaluation of thermal load during laser corneal refractive surgery using infrared thermography

Infrared thermography is used for evaluation of the mean temperature as a measure of thermal load during corneal refractive surgery. An experimental method to determine emissivity and to calibrate the thermografic system is presented. In a case study on the porcine eye two dimensional temperature distributions with lateral resolution of 170 μm and line scans with temporal resolution of 13 μs are discussed with respect to the meaning of mean temperature. Using the newest generation of surgery equipment it is shown, that the mean temperature rise can be kept below 5 °C during myopic laser in situ keratomileusis (LASIK) treatments corresponding to an aberration-free correction of ?2.75 diopter.     

Development of scattering near-field optical microspectroscopy apparatus using an infrared synchrotron radiation source

We report the status of a scattering near-field microspectroscopy apparatus developed at SPring-8 using an infrared synchrotron radiation (IR-SR) source. It consists of a scattering type scanning near-field optical microscope and a Fourier transform infrared spectrometer. The IR-SR is used as a highly brilliant and broad-band IR source. This apparatus has potential for application in near-field spectroscopy with high spatial resolution beyond the diffraction limit. In order to eliminate background scatterings from the probe shaft and/or sample surface, we used higher harmonic demodulation method. The near-field spectra were observed by 2nd harmonic components using the lock-in detection. The spatial resolution of about 300 nm was achieved at around 1000 cm^? 1 (10 μm wavelength).     

Ultrasonic imaging using air-coupled P(VDF/TrFE) transducers at 2 MHz

A reflection non-contact ultrasonic microscope system working both in amplitude and phase difference modes at 2 MHz has been developed using an air-coupled concave transducer made of piezoelectric polymer films of poly(vinylidene fluoride/trifluoroethylene) [P(VDF/TrFE)]. The transducer is composed of three 95 μm-thick P(VDF/TrFE) films stacked together, each of which is activated electrically in parallel by a driving source. The transducer has a wide aperture angle of 140° and a focal length of 10 mm. The measured two-way transducer insertion loss is 80 dB at 1.83 MHz. Despite 20 dB higher insertion loss than that estimated from Mason’s equivalent circuit, we have obtained clear amplitude acoustic images of a coin with transverse resolution of 150 μm, and clear phase difference acoustic images of the rough surface of a paper currency bill with depth resolution of sub-micrometer. Using two planar transducers of P(VDF/TrFE), we have also successfully measured in through-transmission mode the sound velocity and absorption of a 3 mm-thick silicone-rubber plate. The present study proves that, owing to its low acoustic impedance and flexibility, P(VDF/TrFE) piezoelectric film is very useful for high frequency acoustic imaging in air in the MHz range.