Robert M. Hammaker

Hadamard transform Raman imagery with a digital micro-mirror array

Abstract Our previous efforts in Hadamard transform Raman imaging in the visible spectral region began with stationary two-dimensional (2D) Hadamard encoding masks and evolved to moving 2D Hadamard encoding masks. We have now advanced to using a spatial light modulator developed by Texas Instruments, herein called a digital micro-mirror array (DMA), as a computer-controlled 2D Hadamard encoding mask. The aluminized mirrors in the DMA are 16 um square and rotatable by ±10° from an intermediate position. The +10° position of a micro-mirror directs its spatial resolution element onto the detector and the −10° position of a micro-mirror directs its spatial resolution element away from the detector. The heterogeneous samples investigated were three layers of immiscible liquids (benzene–water–nitrobenzene) and a layer of solid benzoic acid stuck to a piece of double sided tape with a 1.0 mm 2 chip of naphthalene pressed onto the layer of benzoic acid near one corner of the benzoic acid layer. Macroscopic images of the various components in these samples have been generated with a spatial resolution of 340 um. Spectra of individual pixels at the sample plane have been obtained for the sample of immiscible liquids. Images of liquid and solid heterogeneous samples and spectra of individual pixels at the sample plane can be obtained by Hadamard transform Raman imaging using a DMA as a 2D Hadamard encoding mask that operates rapidly and reliably.

Multiplex advantage in Hadamard transform spectrometry utilizing solid-state encoding masks with uniform, bistable optical transmission defects

The effect of a uniform bistable optical transmission defect in the encoding mask on the multiplex efficiency is investigated for solid-state Hadamard transform spectrometry with thermal detection. It is demonstrated that encoding masks which possess nonideal optical transmission properties, i.e., bistable transmission defects, need not impare the multiplex capability provided a sufficient number of resolution elements are multiplexed. Application to the SNR of a general algorithm for the calculation of the average mean square error in the estimate of the spectrum shows that reasonable SNR improvements can be expected when compared to conventional dispersive instruments.

Temporal systematic errors using stationary Hadamard encoding masks

Abstract Temporal systematic errors result from the use of a stationary Hadamard encoding mask in a Hadamard transform spectrometer when the time between encodements is made too short relative to the mask response time. These errors have been characterized and an empirical method has been developed to correct for the resulting artifacts appearing in the spectra. It is then possible to operate the Hadamard transform spectrometer with a shorter data acquisition time. Typical examples are presented and discussed.

Potential for Using a Digital Micromirror Device as a Signal Multiplexer in Visible Spectroscopy

A digital micromirror device (DMD™) was tested to demonstrate its potential as a multiplexing device for the simultaneous detection of visible electromagnetic radiation. Using a Visual Basic program, four sections of the DMD were illuminated by a light source and each region of mirrors was modulated at different low frequencies (14.92, 20.00, 25.00, and 34.48 Hz). A time-domain, multiplexed signal was collected from the sectors and a Fourier transform was performed on these data. The resulting frequency-domain spectrum showed that signal intensities correlated well with what was expected. Three different times were used to establish the best frequency resolution. Using this calculated frequency resolution, a 16-s scan could allow simultaneous detection of up to 240 emission/absorption wavelengths. Data collected also shows the selectivity of micromirror regions and the ability to choose specific regions of the micromirror plane, which could be valuable for a number of spectroscopic techniques.

Near-infrared Hadamard transform Raman spectrometry

Abstract Hadamard transform spectrometry using a liquid crystal optical shutter array (LC-OSA) as a stationary Hadamard encoding mask is shown to be a viable technique for near-IR Raman spectrometry with the 1064-nm line of a Nd:YAG laser. Spectra are presented and discussed and future plans are outlined.

A Method of Predicting Point and Path- Averaged Ambient Air VOC Concentrations, Using Meteorological Data

A method of predicting point and path-averaged ambient air VOC concentrations is described. This method was developed for the case of a plume generated from a single point source, and is based on the relationship between wind directional frequency and concentration. One-minute means of wind direction and wind speed were used as inputs to a Gaussian dispersion model to develop this relationship. Both FTIR spectrometry and a whole-air sampling method were used to monitor VOC plumes during simulated field tests. One test set was also conducted using only whole-air samplers deployed in a closely-spaced network, thus providing an evaluation of the prediction technique free of any bias that might exist between the two analytical methods. Correlations between observed point concentrations and wind directional frequencies were significant at the 0.05 level in most cases. Predicted path-integrated concentrations, based on observed point concentrations and meteorological data, were strongly correlated with observed...

A new stationary Hadamard encoding mask for near- infrared Hadamard transform Raman spectrometry

Abstract Near-infrared Hadamard transform Raman spectrometry was performed to demonstrate the advantages gained using a recently developed 255 element polymer-dispersed-liquid-crystal (PDLC) optical-shutter-array as a stationary Hadamard encoding mask. Spectra presented illustrate the improvements the PDLC encoding mask has made in comparison with a 127 element cholesteric liquid crystal display used previously. Examples of the multiplex advantage and a selective multiplex technique are presented and discussed.

Hadamard Transform Spectrometry: Application to Biological Systems, a Review

Hadamard transform spectrometry (HTS) using a liquid crystal spatial light modulator (LC-SLM) as a stationary encoding mask is shown to be a viable technique for visible and Raman spectrometry. HTS is a multiplexing method that has many advantages similar to Fourier transform spectrometry. The theory of HTS is presented in simple detail using weighing designs to show the inherent advantages of the technique. Visible Hadamard transform Raman (HT-Raman) spectra are obtained and spectral subtraction is performed on a two liquid mixture.

Evaluation of emissions from remedial activity at a former manufactured gas plant by open-path Fourier transform infrared spectroscopy

Open-path Fourier Transform Infrared Spectroscopy (OP-FTIR) was used to conduct an air monitoring survey at a Fourier manufactured gas plant (FMGP) superfund site. This survey was performed in support and at the request of the Waste Management Division, U.S. EPA, Region VII. A three day study was conducted in which the OP- FTIR instrument was operated at several fenceline locations around the perimeter of the site in order to detect and quantify benzene emissions. Results of the survey indicated that benzene emissions correlate very closely with site excavation and soil processing activities. Varying concentrations of benzene were detected were and quantified in the field in near-real time. Laboratory analysis of the field data also indicated concentrations of ammonia and toluene at levels above the instrumental detection limit.

Optimization of a Fourier transform infrared spectrometer during on-site pollution analysis

The field transportable Fourier transform infrared (FT-IR) spectrometer system developed at Kansas State University is now finishing the testing stage. The testing stage consisted of three parts: the measurements of (1) controlled releases of volatile organic compounds (VOC), (2) uncontrolled VOC releases at well documented sites, and (3) uncontrolled VOC releases at complex sites with little or no precharacterization1. Some measurements have been acquired in all three categories with most of the data acquisition taking place in the first two categories, which are discussed in these proceedings. These tests were developed to validate the qualitative and quantitative capabilities while enhancing the versatility and detection limits of the spectrometer system. The controlled VOC releases, for the most part, took place at the University of Kansas (KU). The KU tests utilized a co-monitoring technique, evacuated stainless steel canisters followed by GC/FID analysis, during the acquisition of the infrared data. The ability to monitor the concentrations of the released plume with another technique allowed for the comparison and examination of how varying parameters can affect the infrared spectrometer technique. The varying parameters that were addressed were wind, path length, temperature, barometric pressure, water and carbon dioxide concentration, and air borne particulates. One set of uncontrolled releases occurred at an active production facility. A list of the possible compounds that might be observed from the facility directly due to production was obtained. Infrared measurements were acquired at two different setup geometries down wind and one setup geometry up wind. The three path lengths were 390 meters, 500 meters, and 412 meters respectively. During these measurements two series of canister samples were obtained down wind and one series of canister samples were obtained up wind. The analyses of these canisters, on-going at this writing, is being performed by GC/FT-IR (matrix isolation). When the analysis from this method is complete the results will be compared. These two different data acquisitions have led to much insight into the capabilities of the spectrometer system and how varying parameters can affect the FT-IR spectrometers performance. Preliminary analysis of the spectroscopic data from both data acquisitions will be discussed.