e-book Introduction to Imaging Spectrometers (Tutorial Texts in Optical Engineering)

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Trails of evidence are followed through correspondence between alleged Communist Party members and sympathizers, as well as interviews with associates of the accused. The archive is an invaluable resource on the Second Red Scare and the internal politics of the United States during the early years of the Cold War. The purpose of the organization was to give voice to the returning servicemen who opposed the on-going war in Southeast Asia.

The collection also includes surveillance on a variety of other antiwar groups and individuals, with an emphasis on student groups and Communist organizations. The Amerasia Affair was the first of the great spy cases of the postwar era. Unlike Alger Hiss or the Rosenberg cases, it did not lead to an epic courtroom confrontation or imprisonment or execution of any of the principals. Posted July 10, by Tim Hagan. These documents touch upon all aspects of U. S, and selected foreign countries. The method of claim 15 further comprising the steps of: converting data collected by said two-dimensional array of detectors into the spectral absorption image.

The method of claim 16, wherein said step of converting comprises the steps of: retrieving intensity information from said two-dimensional array of detectors; and. An imaging attenuated total reflection ATR micro-spectrometer comprising: a radiation source;. USP true USA en. JPB2 en. DEB9 en. GBB en. Single pass attenuated total reflection fourier transform infrared microscopy apparatus and method for identifying protein secondary structure, surface charge and binding affinity.

USB2 en. Apparatus for measuring biological information and method for measuring biological information. Method and system for diffusion attenuated total reflection based concentration sensing. USB1 en. System for sequentially providing aberation corrected electromagnetic radiation to a spot on a sample at multiple angles of incidence. Rotating or rotatable compensator system providing aberation corrected electromagnetic raadiation to a spot on a sample at multiple angles of a incidence. Method and apparatus for evaluating a sample through variable angle Raman spectroscopy.

US6141100A - Imaging ATR spectrometer - Google Patents

Correlation interferometric methods, devices and systems for low cost and rugged spectroscopy. Manufacturing method of evaluation method and the applied SiC single crystals that of SiC single crystal. Optical element for attenuated total reflection, a method of spectroscopic analysis and a mould for making this element. Vertical double-pass multiple reflection cell for internal reflection spectroscopy. Device for the laterally resolved investigation of a laterally heterogeneous ultrathin object layer. Bhargava, Rohit et al. Chalmers, John M.

Ciurczak, Emil W. Colarusso, Pina et al. Kidder, L. Kidder, Linda H.

Keywords/Phrases

Koenig, J. Marcott, C. Marcott, Curtis et al. Snively, C. Diffusion of Liquid Crystals into Polymers, "Macromolecules,vol. Diffusion of Liquid Crystals into Polymers, Macromolecules, vol. Sweedler; " High Detectors " Analytical Chemistry, vol. Sweedler; High Detectors Analytical Chemistry, vol. Wolfe, William L. TT25 ed. Wright N. Single pass attenuated total reflection infrared analysis identifying protein secondary structure, surface charge and binding affinity. Systems and methods for attenuated total internal reflectance ATR spectroscopy. GBA en. DEB4 en.

DEA1 en. JPHA en. GBD0 en. Tyo et al. USREE en. EPB1 en. Apparatus and method for performing high spatial resolution thin film layer thickness metrology. USA1 en. Infrared radiation sources, sensors and source combinations, and methods of manufacture. CAC en. Compact prism spectrograph suitable for broadband spectral surveys with array detectors. EPA1 en. It can be seen as the filter response of the OSA, and can be defined as the ratio between the power at a given distance from the peak and the power at the peak.

If the ORR is not higher than the optical signal-to-noise ratio of the source to be tested, the measurement will be limited by the OSA's response, rather than reflecting a true property of the tested source. The table to the right provides an example. To align the input light source with respect to the OSA's internal interferometer, a red, Class 1 alignment beam, which is activated by a rotating switch, is emitted from the aperture.

The input source should be made collinear to the alignment beam for the OSA to provide optimal measurement accuracy. Four taps around the input aperture enable compatibility with our 30 mm cage system ; use cage rods no shorter than 1. The interferometer assembly normally "floats" on gel bushings inside the case.

When using the free-space input, it may be desirable to lock the interferometer to the optical table surface. When the interferometer is locked to an optical table, the beam height is 61 mm 2. We recommend only using the posts supplied with the OSA to secure it to the optical table.

We also do not recommend using long optical posts to raise the OSA off of the optical table surface.

Introduction to imaging spectrometers / William L. Wolfe - Details - Trove

Includes a GUI for controlling the OSA, as well as a "virtual device" mode ideal for evaluating the software prior to purchase. This software features a straightforward, intuitive, responsive interface that exposes all functions in one or two clicks. We regularly update this software to add significant new features and make improvements suggested by our users. Several key functions are explained in the Tutorial Videos tab.

Please see the Programming Reference tab on the software download page for more information and download links. The text below summarizes several key features of the OSA software suite. Complete details on the software are available from the manual PDF link. In the main window, it is possible to average multiple spectra; display the X axis in units of nm, cm -1 , THz, or eV; compare the live spectrum to previously saved traces; perform algebraic manipulations on data; and calculate common quantities such as transmittance and absorbance.

Robust graph manipulation tools include automatic and manual scaling of the displayed portion of the trace and markers for determining exact data values and visualizing data boundaries. Automated peak and valley tracking modules see the screenshot to the right identify up to peaks or valleys within a user-defined wavelength range and follow them over a long period of time. Statistical parameters of traces such as standard deviations, RMS values, and weighted averages are available, and a curve fit module fits polynomials, Gaussians, and Lorentzians to the spectrum or interferogram.

Acquired data can be saved as a spectrum file that can be loaded quickly into the main window. Adjustable Sensitivity and Resolution Settings The scan sensitivity and resolution can be adjusted by the user to balance the needs of the experiment against the data acquisition rate. These settings vary the number of data points per interferogram from 0. The sensitivity setting modifies the range of detector gain levels, while the resolution setting controls the optical path difference OPD.

The table in the Specs tab shows how the data acquisition rate depends upon the chosen settings. This mode allows the system to resolve a fraction of a fringe in the interferogram, using the phase-locked loop that is generated by the internal stabilized reference HeNe laser see Interferogram Data Acquisition in the Design tab for details. The uncertainty in the measurement is continuously determined and displayed as gray numbers. As shown in the image to the right, a built-in module plots the output of the wavelength meter measurement as a function of time.

If the software determines that the wavelength meter will give inaccurate results as it would for broadband sources , it is automatically disabled. Coherence Length Module for Broadband Sources Because Thorlabs' OSAs obtain the raw interferogram of the unknown source as opposed to grating-based spectrum analyzers, which cannot offer this capability , the software is able to calculate the coherence length of the input signal, as shown by the screenshot to the right. The ability to view the raw interferogram in real time allows the user to confirm the coherence length reported by the software and adjust the signal amplitude to avoid saturation.

Apodization and Interferogram Truncation Since the resolution of any Fourier-transformed spectrum is intrinsically constrained by the finite path length over which the interferogram is measured, the software implements several functions to account for the effect of the finite path length on the spectrum that is obtained. The user may select from a number of apodization methods dampening functions , including cosine, triangular, Blackman-Harris, Gaussian, Hamming, Hann, and Norton-Beer functions, and the effective optical path length can also be shortened to eliminate contributions from high-frequency spectral components.

Spectroscopic Analysis from HITRAN Reference Database In environmental sensing and telecom applications, it is often useful to identify atmospheric compounds such as water vapor, carbon dioxide, and acetylene whose absorption lines overlap with that of the unknown source being measured. Some example measurements are shown below. The OSA software includes built-in support for HITRAN line-by-line references , which can be used to calculate absorption cross sections as a function of vapor pressure and temperature.

The predictions can be fit to the measured trace for comparison, and fits using mixtures of gases are supported. See the Gas Spectroscopy tab for an example setup. To help customers learn about, use, and understand the Optical Spectrum Analyzer software, we have prepared several short narrated videos that describe the basic aspects of the software and the optimal settings for common types of measurements.

Although the OSA model shown in the videos has been discontinued, the principles of operation have not changed. Full Screen, p Resolution Recommended In order to be able to read the text in the videos, we strongly recommend viewing these videos at full screen, p resolution. To expand the video to full screen, click on the button shown in the screenshot above.

Pressing the Escape key will restore the video to its original size. To choose p resolution, use the Quality menu, which appears after clicking on the gear icon, as shown by the screenshot to the right. Measurement of pulsed spectra suffers from several issues that must be overcome for accurate measurements; for instance, "spectral ghosts" arise due to the pulsed nature of the source as well as the varying optical path difference OPD of the OSA. In addition, the noise floor for pulsed sources is much higher than that for CW sources.

One method for measuring pulsed sources with the OSA involves taking several successive measurements at the four different sensitivity levels; the minimum at each wavelength of these four traces is used to form a combined spectrum, which suppresses the spectral ghosts. The following tutorial explains the rationale of this technique and the pulsed sources for which it is useful. In summary, for pulse rates over 30 kHz, standard mode can be used because the repetition rate is greater than the detectors' bandwidth.

For broadband signals with low repetition rates, care must be taken to ensure that the "zero burst" of the interferogram coincides with one of the pulses. Also, when using a pulsed source "Automatic Gain" does not work properly, so the user must monitor the interferogram and manually set the gain so that a strong, but not saturated, signal is obtained. Impact of a Pulsed Source on the Interferogram and Spectrum As the Optical Path Difference OPD continuously changes during an interferogram measurement, a pulsed light source effectively modulates the interferogram.

These slots correspond to OPDs when no light can be measured by the detector assembly. The resulting interferogram in this case is the true interferogram masked with the pulsed signal. Figure 1 shows measured interferograms and the corresponding spectra for a light source in CW and pulsed operation. Although the spectrum of the light source is expected to be the same for CW and pulsed operation ignoring small changes in the peak shape and position due to, for example, a decreased LD chip temperature resulting from the pulsed drive , additional frequency artifacts appear symmetrically about the expected peak due to the modulation in the pulsed interferogram.

These "spectral ghosts" are a result of the temporal, rather than the spectral, behavior of the source. Figure 1: Measured interferograms and spectra for a narrowband light source in CW Top and pulsed at 20 kHz Bottom operation. The square wave modulation of the interferogram induces the spectral ghosts shown in the bottom left plot.

Mathematically, the resultant spectrum of a pulsed source can be described by a convolution between the spectrum of the light source and the spectrum corresponding to the pulses. Figure 2 shows how the behavior of the spectral ghosts as a function of the pulse repetition rate for a narrowband source. In the figure, the spectra were measured for 55 pulse repetition rates between Hz and kHz for a nm DFB laser diode.

We have offset the y-axis such that the true peak the light gray horizontal line has been centered at a relative frequency of 0 THz. The second region starts above 3 kHz, when the first spectral ghosts have moved beyond the spectral range of the OSA. The "slot period" of the interferogram, determined by the pulse repetition rate of the light source and the OPD rate of the OSA, affects the positions of the spectral ghosts. A shorter slot period yields a larger spectral distance between the true peak and the first order ghost peaks.

In Thorlabs' OSAs, the OPD sample rate is given by the speed of the moving carriage which can be controlled by the user indirectly through the sensitivity setting. The higher the sensitivity setting is, the speed of the moving carriage will be slower. Thus, the use of the "High" sensitivity mode of the OSA will provide the shortest slot period i. In pulsed mode, the software acquires four spectra with different sensitivity settings or OPD sample rates and filters out the changing spectral features. The sensitivity is first set to low, followed by Medium-Low, Medium-High, and High before it again is set to Low yielding a periodically changing sensitivity.

The captured spectra are then combined using the minimum hold function. The spectral ghosts Figure 4 , whose positions depend on the sensitivity setting the OPD rate , can then be reduced in the measurement as shown in Figure 4. It is important to note that the Pulse Mode button is found under the "Sweep" menu and can be started only after the current sweep has been completely stopped.

Five averaged spectra were captured for each light source setting; the CW spectra were acquired in high sensitivity mode, and the pulsed spectra were recorded in both high sensitivity and pulsed mode. It is important to note that the pulsed mode does not allow averaging. Instead the minimum hold function was used for 5 sets of spectra from the four different sensitivity settings.

Figure 5 shows the resultant spectra for the source in CW mode as well as four different pulse repetition rates between Hz and kHz. As the pulse rate increases, the spectral ghosts as recorded in the high sensitivity mode move further and further away from the true laser peak until nearly identical spectra are obtained at kHz. Figure 5: Spectra from measurements of a nm Pulse repetition rates shown left to right : Hz, 1 kHz, 13 kHz, and kHz.

Black line: CW measurement; blue line: pulsed source measured with high sensitivity; red line: pulsed source measured using the pulsed mode. The lower plots are the same data set as the upper plots only on a shorter frequency scale. Broadband Light Source A gain chip was driven in amplified spontaneous emission ASE mode to create a broadband light source centered at nm A total of 10 averaged spectra were acquired using high sensitivity CW and pulsed sources and the pulsed mode pulsed source. Because pulsed mode does not allow averaging, the minimum hold function was used to acquire five sets of the four different sensitivity settings.

US6141100A - Imaging ATR spectrometer - Google Patents

In general, the spectral ghosts are less visible for the broadband peak compared to a narrowband peak. Similar to the narrowband source, the spectral ghosts move farther and farther away from the true peak with increasing repetition rate. For a repetition rate of kHz both the measurement using high sensitivity and pulsed mode agree well with the CW measurement. As seen, the shape of the peak is slightly different for the CW spectrum compared to the pulsed spectrum.

This is not related to the behavior of the OSA but due to a true change in the peak during pulsed operation, e. Figure 6: Measured spectra from a pulsed broadband source with a center wavelength frequency of nm The pulse repetition rates shown are Hz, 1 kHz, 13 kHz, and kHz. Black line: CW; blue line: pulsed source measured using high sensitivity; red line: Pulsed Mode. It is extremely important to note that in general, one has to be careful when measuring broadband peaks at low repetition rates.

Since most of the information in the interferogram is located about the zero burst, the peak can be completely missed if the zero burst coincides with no light falling on the detector as shown in Figure 7. Light output from the laser was collected with a fiber patch cable SM fiber; 0. Figure 8 shows the interferogram collected during acquisition, which does not contain any empty slots.

Lecture 6A Fourier Optics Basics

This was expected as the 85 MHz repetition rate of the laser is well beyond the 40 kHz bandwidth of the OSA's detectors. Furthermore, the spectrum measured by the OSA agrees very well with the reference spectrum captured using a grating-based OSA that is scanned slowly enough to provide adequate signal for each wavelength measured. As shown in the table to the right, many of Thorlabs' Optical Spectrum Analyzers OSAs offer detection extending into the mid-infrared MIR region of the spectrum, where many gaseous species characteristically absorb.

These files can be fit to measured traces to identify unknown gases. With the ability to fit multiple analytes simultaneously and built-in hose connections compatible with Thorlabs' Pure Air Circulator Unit for purging the interferometer's cavity of trace gases, these OSAs are ideal for use in home-built gas detection setups. Experimental Setup A sample detection setup is shown below. Broadband MIR light generated by a Stabilized Light Source is emitted from a zirconium fluoride fiber , collimated, then sent into a multipass cell containing the gas analyte in a sample chamber.

Each end of the chamber is sealed by an airtight, transparent window. Gold mirrors on each side of the chamber provide multiple reflections that increase the sensitivity of the measurement; the mirror closer to the light source has a center hole to allow the optical path to enter and exit the chamber. Light exiting the detection setup is collimated by a long-focal-length lens and reflected by a D-shaped mirror into the free-space port of the OSAC.

The temperature inside the chamber is elevated and held constant in order to prevent the gas's absorption lines from shifting during the measurement. Assigning Peaks in an Unknown Spectrum Once the experimental spectrum is obtained, the user chooses a gas or gas mixture that is believed to be present inside the sample chamber, as shown in the figure below to the left. There is no limit to how many species can be considered in the fit, but the fit is more likely to converge when fewer species are chosen.

Previously saved spectra in the OSA file format can also be used as references. The user may optionally allow the software to shift the reference spectrum in wavelength in order to account for measurement effects related to the sample environment. In the case of gas mixtures i.


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As shown in the figure below to the right, the output of the fit operation is a graph comparing the measured spectrum, each scaled and possibly also shifted reference spectrum, and the sum of the scaled reference spectra. Need a Quote? Thorlabs' in-stock OSA models offer a number of detection options for various experimental situations.

We invite customers whose needs are not addressed by these models to tailor an OSA to a specific application by working with our engineering and manufacturing team. For customers who use these instruments for sample characterization, our software team has implemented user-designed data analysis modules within the standard OSA software suite. We have also worked with our customers to choose detector elements targeted at specific light sources and analytes. The graphs below were obtained from custom-built OSAs that were designed for especially high detection sensitivity.

Our engineers are well-versed in the tradeoffs between detection bandwidth, sensitivity, and linearity, and can make recommendations based upon the needs of the application and prior customers' experiences. By constraining the OSA's design for a particular use case, additional performance enhancements for that application can be realized.

If you would like to discuss a custom OSA, please contact us with your experimental requirements. For MIR applications that require such peaks to be resolved, we have qualified two MCT HgCdTe detector elements which achieve significantly lower noise floors, in exchange for a narrower wavelength range and lower maximum input power. We provided a custom-built OSA with a greatly reduced noise floor as compared to the OSAC, which easily detected the predicted signal.

Thorlabs' OSAs measure the optical power of both narrowband and broadband sources as a function of wavelength. The maximum spectral resolution of 7. Single mode patch cables provide the highest contrast. OSAs with other fiber input receptacles are available by contacting Tech Support. To align the input light with respect to the OSA's internal interferometer, a red, Class 1 alignment beam, which is activated by a rotating switch, is emitted from the aperture.

See in the video above for a demonstration. The input beam should be made collinear to the alignment beam for the OSA to provide optimal measurement accuracy.