Bio-rad Laboratories, Inc.

Block Engineering, LLC

Varian Australia Pty Ltd

Raul Curbelo

R Brough Turner

David C Brown

David B Johnson

Warren R Howell

David E Abrams

E Michael Burka

David Abrams

A source for reducing drift of a hot spot by producing infrared (IR) light with an insulating housing; an electrical power supply; first and second resistance elements having first and second resistivities; a third resistance element having a third resistivity; the third resistance element disposed between the first and second resistance elements, with the resistivity of the third resistance element having a value greater than the resistivity of both the first and second resistance elements. Alternatively, the first and second resistance elements can have cross-sectional areas that are greater than that of the third resistance. A method of reducing drift of a hot spot in a radiating element of a source of IR illumination by applying constant polarity substantially constant direct current from the power supply and reversing polarity in less than 24 hours, by a square wave AC source, or a Class E amplifier at constant power.

Infrared source for spectrometers

Method and apparatus for providing an imaging attenuated total reflection (ATR) spectrometer which provides faster measurement speed and better spatial resolution than systems collecting an equivalent amount of data using conventional, non-imaging ATR methods and systems. Apparatus includes a radiation source, an interferometer coupled to the radiation source which produces a spectrally-multiplexed input beam of radiation, an internal reflection element (IRE) engaging a sample-under-test, a focal plane array detector, a first optical system adapted and positioned to direct and concentrate the input beam through the rear surface of the IRE towards a contact area of the sample such that an angle of incidence of said input beam at the front surface is equal to or greater than the critical angle for the IRE, and a second optical system adapted and positioned to collect reflected radiation from the contact area and image the same onto the focal plane array detector.

Imaging ATR spectrometer

A technique for extracting the impulse response of a sample of interest includes corresponding measurements made with the sample of interest and a reference sample. At each of a series of steps in an FT-IR spectrometer, the sample of interest is illuminated with an excitation pulse of infrared radiation, acoustic signals having a time dependence o.sub.S (t) arising from the excitation pulse are captured, and a Fourier transform O.sub.S of o.sub.S (t) is computed. At each of a series of steps in the FT-IR spectrometer, the reference sample is illuminated with an excitation pulse of analytic radiation, acoustic signals having a time dependence O.sub.R (t) arising from the excitation pulse are captured, and a Fourier transform O.sub.R of o.sub.R (t) is computed. For each step, an inverse Fourier transform of the ratio O.sub.S /O.sub.R is computed to provide a series of values s(t.sub.i) for a series of times t.sub.i. These values s(t.sub.i) represent the impulse response s(t) of the sample of interest for the mix of optical frequencies for that retardation value. Interferograms are processed to provide photoacoustic spectra.

DSP technique for photoacoustic spectroscopy (PAS) sample pulse response

Digital signal proceessing (DSP) techiques for performing multiple modulation measurements with a polarization photoelastic modulator (PEM) in a step-scanning FT-IR spectrometer. The frequency and phase of the PEM drive signal are extracted from the digitized data collected for the actual measurement. This can then be used to perform the desired analysis of the polarization signals (e.g., CD,LD, DIRLD). This is accomplished by successively refining an initial estimate of the PEM frequency (typically starting at the nominal PEM frequency .omega..sub.0, or at the value determined from the previous step). This is done by using the current estimate of the PEM frequency to compute a phase error, and then using the computed phase error to refine the estimate of the PEM frequency. The phase errors are computed using different sets of samples in the sampling interval.

Digital signal processing (DSP) techniques for FT-IR multiple modulation

By considering a transient signal as merely another signal in a linear, shift-invariant system representing a step-scanning Fourier transform spectrometer, the present invention characterizes the transient signal and then compensates for its effect on the measurement by employing various signal processing techniques. Thus, according to one aspect of the present invention, it provides a method for obtaining the spectrum of the desired signal by subtracting the Fourier transform of the transient signal from the Fourier transform of the composite signal output from the detector (i.e., the signal containing both the desired signal and the transient signal). According to another aspect of the present invention, it provides a method for deriving an estimate of the Fourier transform of the transient signal from the Fourier transform of the composite signal.

Digital signal processing for a FT-IR spectrometer using multiple

For a step-scanning Fourier transform spectrometer comprising an interferometer, a detector, and a digital signal processor (DSP), a method for measuring a response of a sample to multiple modulations is disclosed. In one embodiment, the method comprises the steps of utilizing the DSP to measure a phase modulation angle and a sample modulation angle; obtain an interferogram that corresponds to a calibrated static sample response by using the measured phase modulation rotation angle; obtain another interferogram which corresponds to the calibrated dynamic sample response by using both the measured phase and sample modulation rotation angles; and computing one or more spectra from the interferograms which indicates the calibrated response of said sample to the multiple modulations.

Triple modulation experiment for a fourier transform spectrometer

A laser beamsplitter for generating a plurality of parallel beams comprises a first beamsplitter and a second beamsplitter. The first and second beamsplitters are manufactured from glass flats having precisely parallel faces, wherein the front surface is coated with a reflective coating and the back surface is coated with a beamsplitter coating such that an initial laser beam passing through the first beamsplitter at a preferred angle of incidence is split into a first beam and a second beam. The second beamsplitter is positioned relative to the first beamsplitter such that the first beam passes through the second beamsplitter and is split into a third beam and a fourth beam. The parallelism of the output beams are determined by the parallelism of the glass flats, and no manual adjustments need to be made. The second, third, and fourth beams, if shone onto a surface orthogonal to the path of the initial beam, display three points that define a triangle, and preferably an equilateral triangle. The coatings on the surfaces of the first and second beamsplitters are chosen to provide three output beams having substantially the same intensity.

Laser beamsplitter for generating a plurality of parallel beams

Alignment circuity and calibration method for a scanning interferometer. Phase shifts are introduced into the alignment servo to maximize overall modulation efficiency.

Technique for achieving preferred optical alignment in a scanning

Digital signal processing technique for a FT-IR spectrometer using

A technique for improving the resolution of an A/D converter (30). The input analog signal is sampled to generate an analog level and the analog level is held (20) for an interval. A dither signal (22) is superimposed (23) on the held level to generate a fluctuating voltage. This fluctuating voltage is then sampled (25) a plurality of at least N times, and N sampled values are communicated to the A/D converter (30) so that N digitized values are generated. These digitized values are averaged (32) to provide an output having a digitization error reduced by a factor of up to N.sup.1/2.

Technique for improving the resolution of an A/D converter

A technique that corrects photodetector non-linearity without increasing the noise level in the detector signal. The detector is coupled to a preamplifier characterized by the absence of positive feedback, and the preamplifier signal is communicated to a linear amplifier whose output signal is then digitized. The digitized signal is then transformed according to stored calibration information that is representative of the non-linear characteristic of the photodetector. The transformed digitized value thus exhibits a linear characteristic as a function of the intensity of the light source. A number of embodiments perform the correction in hardware before digitizing the signal.

Techniques for correcting non-linearity in a photodetector using

A fast and effective way to step a relative position quantity by a reference interval. Each step in relative position includes open-loop and closed-loop control intervals. The invention contemplates an actuator capable of changing the relative position and a closed loop servo that acts on the actuator to keep the relative position centered on the nearest one of a series of reference values separated by the reference interval. The actuator is preferably capable of a fast response. Stepping the relative position is accomplished as follows, assuming an initial condition where the servo has locked the relative position to a particular initial reference value. First, the actuator is caused to change the relative position by an amount approximately equal to the reference interval in a manner that the servo cannot track the change, such as by disabling the servo. Servo control is then re-established, at which point the servo operates to keep the relative position centered on the nearest reference value. Servo control is maintained until a new step is required, at which time the process is repeated.

Step scanning technique for interferometer

The present invention provides a technique for improving the resolution of an A/D converter. The input analog signal is sampled to generate an analog level and the analog level is held for an interval. A random noise signal having zero average value is superimposed on the held level to generate a fluctuating voltage. This fluctuating voltage is then sampled a plurality of at least N times, and N sampled values are communicated to the A/D converter so that N digitized values are generated. These digitized values are averaged to provide an output having a digitization error reduced by a factor of N.sup.1/2.

An infrared source that operates at about 1150.degree. C. without the need for water cooling. The source is configured with a small surface area radiating element, energized by a high frequency AC square wave. The frequency of the AC square wave is much greater than the inverse of the filament's thermal time constant so that the temperature is very stable. The radiating element is mounted relative to a concave reflector so that the infrared radiation forms a beam suitable for input to a spectrometer. In a first embodiment, the radiating element is in the form of a wire coil, while in a second embodiment, it is in the form of a cylinder having a central portion of reduced diameter.

Low power infrared source assembly for spectrometer

An interferometer bearing assembly including a fixed glass rail, a movable carriage that carries both the movable interferometer mirror and the drive coil for the linear motor, and a mechanism for biasing the carriage onto the rail. The glass rail has two optically flat faces defining a normally horizontal line of intersection. The carriage is a rigid structure with plastic surface portions that provide a bearing interface for contacting the flat faces of the glass rail. To improve stability and reduce the possibility of any transverse movement, the carriage is downward biased, preferably by providing an overlying glass plate with a downwardly-facing flat surface, and mounting a spring-loaded plastic element to the top of the carriage. The plastic element contacts (and slides along) the flat glass surface and transmits a downward force to the carriage.

Growing community of inventors

Lexington, MA, United States of America

Raul Curbelo