Photoluminescence literature review
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The authors describe a grating spectrometer consisting of a slit, a transmission holographic grating, a lens, and a CCD (charge coupled device) camera. A frame grabber equipped in a computer digitizes the NTSC signal from the CCD camera. The system is relatively small (12.7 cm×17.8 cm×30.5 cm) and light-weight (5.4 kg). The system will measure the output of modern fluorescent or compact fluorescent lamps more accurately than conventional filter-based photometers.
Design rule of optical micro-bench and tolerance of positional error of components assembled onto the bench are investigated in case of simple linear connections of incoming and outgoing optical fibers with and without ball lenses. Since there are many error variables with wide range of values that affects the optical coupling, the efficient array with reduced number of combinations is generated using statistical design of experiment and coupling efficiencies are calculated. From 3d B point, the tolerance of each position error is determined. For the fiber-to-fiber connection with ball lenses, the longitudinal and lateral positional errors have the strong interaction with each other to the coupling efficiency and thus should be be limited simultaneously.
We describe and characterize a multichannel modular room temperature photoluminescence spectroscopy system. This low cost instrument offers minimization of size and complexity as well as good flexibility and acceptable spectral resolution. The system employs an efficient flexible front end optics and a sensitive spectrometer with a charge-coupled device array detector. The spectrometer has no moving parts and is more robust than a scanning system. The scientific motivation was to enable the photoluminescence study of various silicon photonics structures. Typical applications are presented for SiOx (x<2) films. It is demonstrated that high-quality steady state photoluminescence data with excellent signal to noise enhancement capability can be delivered besides the ability to perform simultaneous multiwavelength measurements in one shot. This instrument is shown to be useful for evaluating semiconductor wafers, including those intended for light emitting structures from silicon-based photonic crystals. The design, construction, calibration, and the unique features of this system are presented, and performance tests of a prototype are discussed.
The Spectral Irradiance Monitor: Scientific Requirements, Instrument Design, and Operation ModesEdit
The Spectral Irradiance Monitor (SIM) is a dual Fèry prism spectrometer that employs 5 detectors per spectrometer channel to cover the wavelength range from 200 to 2700 nm. This instrument is used to monitor solar spectral variability throughout this wavelength region. Two identical, mirror-image, channels are used for redundancy and in-flight measurement of prism degradation. The primary detector for this instrument is an electrical substitution radiometer (ESR) designed to measure power levels ∼1000 times smaller than other radiometers used to measure TSI. The four complementary focal plane photodiodes are used in a fast-scan mode to acquire the solar spectrum, and the ESR calibrates their radiant sensitivity. Wavelength control is achieved by using a closed loop servo system that employs a linear charge coupled device (CCD) in the focal plane. This achieves 0.67 arcsec control of the prism rotation angle; this is equivalent to a wavelength positioning error of δλ/λ = 150 parts per million (ppm). This paper will describe the scientific measurement requirements used for instrument design and implementation, instrument performance, and the in-flight instrument operation modes.
Indium Gallium Arsenide Imaging with Smaller Cameras, Higher Resolution Arrays, and Greater Material Sensitivity Edit
Indium Gallium Arsenide (InGaAs) photodiode arrays have numerous commercial, industrial, and military applications. During the past 10 years, great strides have been made in the development of these devices starting with simple 256-element linear photodiode arrays and progressing to the large 640 x 512 element area arrays now readily available. Linear arrays are offered with 512 elements on a 25 micron pitch with no defective pixels, and are used in spectroscopic monitors for wavelength division multiplexing (WDM) systems as well as in machine vision applications. A 320 x 240 solid-state array operates at room temperature, which allows development of a camera which is smaller than 25 cm3 in volume, weighs less than 100 g and uses less than 750 mW of power. Two dimensional focal plane arrays and cameras have been manufactured with detectivity, D*, greater than 1014 cm-√Hz/W at room temperature and have demonstrated the ability to image at night. Cameras are also critical tools for the assembly and performance monitoring of optical switches and add-drop multiplexers in the telecommunications industry. These same cameras are used for the inspection of silicon wafers and fine art, laser beam profiling, and metals manufacturing. By varying the Indium content, InGaAs photodiode arrays can be tailored to cover the entire short-wave infrared spectrum from 1.0 micron to 2.5 microns. InGaAs focal plane arrays and cameras sensitive to 2.0 micron wavelength light are now available in 320 x 240 formats.
We describe a spectrometer employing a microelectromechanical system (MEMS). A torsional micromirror device, which was originally designed for laser scanner applications, has been modified to act as a diffraction grating in a Czerny-Turner setup. This spectrometer system combines the working principle of a scanning monochromator with the compactness of a microsystem. The micromirror device is operated in a harmonic scanning mode at a resonant frequency of 500 Hz, enabling the system to acquire a spectrum per half cycle in one millisecond. The spectra of a calibration source in the visible and near-infrared spectral range as well as simulations concerning the optical system demonstrate the performance of the spectrometer.
Surface Photovoltage Spectroscopy—A New Approach to the Study of High-Gap Semiconductor SurfacesEdit
Surface photovoltage spectroscopy is based on the photostimulated depopulation and population of surface states brought about by sub-bandgap monochromatic illumination, while the over-all number of bulk free carriers remains essentially unchanged. Such transitions and their transients (as determined by changes is the contact potential difference) allow the direct determination of the energy positions and the dynamic parameters of the surface states. Surface photovoltage spectroscopy was successfully applied to the surfaces of CdS, ZnO, and GaAs. A model was developed which accounts for the processes involved in surface photovoltage spectroscopy.
Keeping abreast of the latest techniques and applications on laser spectroscopy. While the general concept is unchanged, new features a broad array of new material, e.g., frequency doubling in external cavities, reliable cw-parametric oscillators, tunable narrow-band UV sources, more sensitive detection techniques, tunable femtosecond and sub-femtosecond lasers (X-ray region and the attosecond range), control of atomic and molecular excitations, frequency combs able to synchronize independent femtosecond lasers, coherent matter waves, and still more applications in chemical analysis, medical diagnostics, and engineering.
A High Resolution Near-Infrared (NIR) Camera has been developed and tested. This NIR camera uses a HgCdTe detector array which allows for imaging at high operating temperatures. The camera's format is 640x512 pixels with an 18 μm pitch. We have obtained high broadband spectral response from 0.3 to 2.0 micron with near 100% optical fill factor. The camera is designed as a turnkey system that uses the industry standard Camera Link digital interface. The electronics are located remotely from the sensor head allowing it to be adapted to existing optical systems. This compact camera has been targeted for military, scientific and telecommunication applications. This paper will detail the measured camera performance.
This study sought to assess the feasibility of using ultraviolet-visible-near infrared (UV-VIS-NIR) spectroscopy to monitor changes in total polyphenol index, color intensity and volumic mass, three indicators of quality during red wine fermentation. Samples (n = 68) collected from eleven tanks during fermentation were scanned in three types of quartz flow cells, path lengths 0.1, 2 and 50 mm, in the UV-VIS-NIR region (200–2,100 nm), using a fiber spectrometer system in transmission mode. Principal component analysis and partial least squares regression were used to interpret spectra and develop calibrations for predicting wine composition during fermentation. Models for the prediction of total polyphenol index displayed coefficients of determination (r2) ranging between 0.21–0.98, whereas values for the standard error of cross-validation (SECV) ranged from 2.29 to 14.91, depending on the spectral region used. Values for the prediction of color intensity were: r2 = 0.56–0.98 and SECV = 0.43–1.88. Corresponding values for volumic mass were r2 = 0.31–0.94 and SECV = 8.71–30.20 g/dm3. These results suggest that UV-VIS-NIR spectroscopy using a miniature fiber optic spectrometer as a promising tool could be used as an alternative method for the rapid monitoring of quality parameters during red wine fermentation.
One of the key requirements to achieve solar conversion efficiencies greater than 50% is a photovoltaic device with a band gap of 2.4 eV or greater. lnxGa1-xN is one of a few alloys that can meet this key requirement. InGaN with indium compositions varying from 0 to 40% is grown by both metal-organic, chemical-vapor deposition (MOCVD) and molecular beam epitaxy (MBE), and studied for suitability in photovoltaic applications. Structural characterization is done using X-ray diffraction, while optical properties are measured using photoluminescence and absorption-transmission measurements. These material properties are used to design various configurations of solar cells in PC1D. Solar cells are grown and fabricated using methods derived from the III-N LED and photodetector technologies. The fabricated solar cells have open-circuit voltages around 2.4 V and internal quantum efficiencies as high as 60%. Major loss mechanisms in these devices are identified and methods to further improve efficiencies are discussed.
Abstract We experimentally demonstrate the III-V nitrides as a high-performance photovoltaic material with open-circuit voltages up to 2.4 V and internal quantum efficiencies as high as 60%. GaN and high-band gap InGaN solar cells are designed by modifying PC1D software, grown by standard commercial metal-organic chemical vapor deposition, fabricated into devices of variable sizes and contact configurations, and characterized for material quality and performance. The material is primarily characterized by x-ray diffraction and photoluminescence to understand the implications of crystalline imperfections on photovoltaic performance. Two major challenges facing the III-V nitride photovoltaic technology are phase separation within the material and high-contact resistances.
A Fourier transform spectrometer with no mechanical moving parts is described. The interferogram is generated spatially by a triangle common-path interferometer and is detected by a self-scanning photodiode array. The spectrum is reconstructed by fast Fourier transform in a microcomputer system. Since no moving part is used and a common-path interferometer is employed for simple, stable, and easy alignment, this spectrometer may be built in a relatively small size and with moderate cost. The self-scanning photodiode array as a multichannel detector may lead this spectrometer to the application to time-resolved spectroscopy. The optical throughput is much larger than that of a multichannel dispersion-type spectrometer, because in the system neither a slit nor an aperture is necessary. The emission spectra of a low pressure mercury lamp and a LED are shown to demonstrate the system performance.
A Fourier transform (FT) apparatus specially dedicated to photoluminescence measurements in the near infrared has been assembled. The details of the experimental setup and a comparison with a conventional dispersive apparatus are discussed. Advantages of the FT approach for photoluminescence measurements as well as warnings about limitations and artifacts are illustrated.
In the spectrometer 1, a lens portion 3 having a spherical surface 35 on which a spectroscopic portion 4 is provided and a bottom plane 31 in which a light detecting element 5 is disposed, has a side plane 32 substantially perpendicular to the bottom plane 31 and a side plane 34 substantially perpendicular to the bottom plane 31 and the side plane 32. Then, a package 11 that houses a spectroscopy module 10 has side planes 16 and 18 respectively coming into planar-contact with the side planes 32 and 34, and contact portions 22 coming into contact with the spherical surface 35. Therefore, the side planes 32 and 34 of the lens portion 3 are respectively brought into planar-contact with the side planes 16 and 18 of the package 11 while bringing the spherical surface 35 of the lens portion 3 into contact with the contact portions 22 of the package 11, that positions the spectroscopic portion 4 and the light detecting element 5 with respect to a light incident window plate 25 of the package 11.
This invention comprises the means for the capture of full spectrum images in an electronic camera without the use of color primary filters to limit the spectral color gamut of the captured image. The fundamental principle of the invention is that each pixel of the image sensor acts as an independent spectrophotometer and spectral separator. Electromagnetic energy enters though a slit or collimating optic. Electromagnetic energy gets diffracted into component spectra by diffraction grating spectrophotometer for each pixel of image Electromagnetic energy leaves diffraction grating at different angles based on wavelength of the energy Spectrophotometer separates light for each pixel into its spectral components onto photodetector line array elements. Individual line array elements which are activated determine the original radiance level of the light source containing that specific wavelength region. The sum of these regions determines the spectral signature of the light at that pixel element. Many pixels arranged in a two-dimensional matrix would generate the image frame. Sequencing frame yields a full-spectrum moving image.
Various embodiments include spectrometers comprising diffraction gratings monolithically integrated with other optical elements. These optical elements may include slits and mirrors. The mirrors and gratings may be curved. In one embodiment, the mirrors are concave and the grating is convex. The mirrors and grating may be concentric or nearly concentric.
The subject invention relates to the design of a compact imaging spectrometer for use in thin film measurement and general spectroscopic applications. The spectrometer includes only two elements, a rotationally symmetric aspheric reflector and a plane grating. When employed in a pupil centric geometry the spectrometer has no coma or image distortion. Both spherical aberration and astigmatism can be independently corrected. The invention is broadly applicable to the field of optical metrology, particularly optical metrology tools for performing measurements of patterned thin films on semiconductor integrated circuits
In accordance with the teachings of the present invention, it has been discovered that an optical analysis that is uniquely based on geometrical rather than diffraction considerations, for the purposes of controlling the size of the region from which the photoluminescence is collected, provides an optical system capable of performing photoluminescence microscopy and/or spectroscopy without the disadvantages of the prior art. It is based, in part, on the use of an optical fiber(s) as a field stop within the detection arm(s) of the optical system for coupling the photoluminescence into an optical spectrum analyzer (OSA) and/or photodetector, wherein the diameter and the numerical aperture of the optical fiber are judiciously chosen to limit the field of view, or the region from which the photoluminescence is collected.
Spatially resolved photoluminescence (PL) apparatus is used for the non-destructive characterization of a semiconductor sample. PL excitation from a diode laser is transmitted through a dichroic coupler and, in turn, over a fiber to a fiber collimator wherein the laser light is collimated into a pump beam prior to entering an air path. The air path is composed primarily of an objective lens. The objective lens focuses the pump beam on the sample surface. The photoluminescence signal emitted by the sample travels the same path but in the opposite direction as the pump beam and is collected by the same fiber as a reflected signal. The dichroic fiber coupler is used to separate the return signal from the pump beam with a low insertion loss for each beam. The return PL signal is fed to an optical spectrum analyzer using a single mode fiber connected to the coupler. The sample is placed on a rotational stage capable of x, y and z movement under computer control.
The conventional grating is substituted by one or more curved prisms in a concentric spectrometer of the type derived from the Offner mirror objective. The curved prisms are known as Fery prisms. The deviations from the concentric form are used as a corrective device. The spectral apparatus is especially suited as an imaging spectrometer having a detector array because the two-dimensional image can be formed in the direction of the spatial coordinate as well as the spectral coordinate without distortions and curvatures.
A photoluminescence sensor for detecting a photoluminescent light from a toluminescent material is disclosed. In a preferred embodiment the photoluminescence sensor comprises: a source of light; a concave mirror having at least one perforation for passing the source light through the at least one perforation; an optical waveguide having proximal and distal ends with the photoluminescent material being disposed at the distal end; an objective for directing the source light into the proximal end of the waveguide; an objective for receiving photoluminescent light and for focusing the photoluminescent light onto the perforated concave mirror; a liquid filter for passing the photoluminescent light reflected from the perforated concave mirror to a detector to detect the photoluminescent light. The sensor can also include a chopper disposed at the output end of the objective for modulating the light source at a select frequency and a lock-in amplifier tuned to measure the output from the detector at the select frequency.
A spectrometer is designed capable of effectively covering the full desired spectral range using an array of multiple diffraction gratings arranged in gradually differentiated angles to diffract certain sub-range of photon wavelengths to the target detectors without relying on mechanically changing gratings or use of any moving parts. The optically subdivided spectral analysis results are then electronically integrated to accurately yield the desired full range spectral measurement at a speed compatible to the limit of optical and digital analyzers' speed of the measuring system without manual adjustment and/or mechanical movement delays.
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- Martin H. Ettenberg, Marshall J. Cohen, Robert M. Brubaker, Michael J. Lange, Matthew T. O’Grady, and Gregory H. Olsen, “Indium Gallium Arsenide Imaging with Smaller Cameras, Higher Resolution Arrays, and Greater Material Sensitivity.” SPIE, vol. 4721, Proc. of SPIE, p. 4721–26, 2002.
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