Analytical Instrumentation : Spectroscopy


Temperature Gradient Handling System for Surface Plasmon Resonance (SPR) Measurements

Researchers in the Department of Chemistry and Biochemistry at the University of Wisconsin-La Crosse have developed a surface plasmon resonance (SPR) based method for measuring, in a single experiment, the temperature dependence of binding kinetics for biomolecular interactions. The method is based on a novel sample handling system that generates a spatial temperature gradient across an SPR sensor and is label free.

Multidimensional Imaging with Improved Contrast

UW–Madison researchers have developed a new coherent multidimensional spectroscopy (CMDS) technique that enhances the image contrast by using multiple frequencies that provide 3-D contrast. The method uses three coherent light pulses (intense light beams) with three different frequencies to interact with multiple functionalities within the molecules (e.g., C-H bonds) to create coherent images that are highly characteristic of specific molecules within sample substructures.

Compact Spectrometer

A UW–Madison researcher has developed a more compact and easily manufactured optical spectrometer. Specifically, the new design includes a filter system that receives and modifies light beams according to frequency. It generates a set of uncorrelated and varying filter spectra over an extremely short optical path. Although the filter spectra are complex and appear largely random, they can be ordered into an absorption spectrum using compressed sensing techniques.

Monolithic Fiber Optic Sensor Assembly for High-Temperature or Corrosive Environments

A UW–Madison researcher has developed a high-temperature U-bench sensor constructed from monolithic optical ceramic material. The supporting structure of the sensor and elements such as two opposed lenses or an opposed lens and mirror are constructed of compatible materials and fused together. The material provides a system robust against high temperatures and temperature changes that might affect precision optical alignment or cause mechanical failure in more traditional sensors.

Multidimensional Fourier Transform Infrared Spectrometer for Cost-Effective Laser Systems

A UW–Madison researcher has developed a simplified and robust multidimensional spectrometer that encodes frequency information into laser pulses traveling along two optical paths. This allows a multidimensional spectrograph to be generated.

Background-Free Absorption Spectroscopy with Undithered Light Sources

UW–Madison researchers have developed a technique for reducing the effect of background radiation in absorption spectroscopy that works with undithered light sources. Versions of the technique utilize a combination of optical delays, a splitter and/or balanced photoreceivers. The simplest implementation combines all three components. Wavelength-swept sensor light is directed through a sample and then split into two paths of different lengths. Each of the paths terminates in one diode of a balanced photoreceiver, which allows direct digitization of the difference in sample response at those two wavelengths. A similar version is based on the split-path delay component but uses a single (not balanced) photoreceiver combined with intensity modulation. Yet another implementation uses a modification of a standard grating spectrometer with a spatial offset in place of the split-path light delay.

All versions of this technique are superior to current background-free techniques because of their inherent stability, simple set-up and ability to work with undithered light sources. By implementing laser swept signal without requiring an additional dithered signal, the processing and recording needed in current modulation techniques are bypassed.

Multi-Spectral Laser with Periodically Poled Crystal Mixer for Carbon Isotope Ratio Measurements

A UW-Madison researcher has developed a technique that uses a single crystal with three separate lasers to create a multi-spectral laser light source.  This set-up allows for a greater modulation range than the standard range for the crystal.  It also is capable of measuring the corresponding absorption lines of two species without requiring two crystals and four lasers or precise determination of the sample temperature.

Reducing the number of crystals and lasers drastically reduces the cost of the spectrographic device and is done by “back bending” the modulation curve of the PPLN crystal.  Three lasers of different frequencies illuminate the crystal to give two different output frequencies.  Nonlinear mixing occurs between the first and second input lasers and the second and third lasers, but not at the second frequency or a range of frequencies between the first and third inputs. 

Methods and Novel Spectophotometer for Achieving Uniform Dispersion of Carbon Nanotubes, Graphene and Nanocellulose

Researchers at UW-Platteville have developed enabling technologies that address the purification and dispersion problems inherent when processing graphene, carbon nanotubes and other nanomaterials. A sensitive photon counting static light scattering (SLS) spectrophotometer was built to collect data for calculating various thermodynamic parameters of dilute samples. The data is used to identify the existence of a solvent resonance whose local extreme identifies the intrinsic property of an ideal solvent (for a given solute). The intrinsic property identified by the solvent resonance can be employed to inform a search for a solvent having the best match to this intrinsic property.

Imaging Spectrometer for Early Detection of Skin Cancer

A UW-Madison researcher has developed a portable imaging spectrometer for the early detection of skin cancer. A handheld scanner uses light emitting diodes to illuminate a region of skin and the reflected light is collected by an objective lens. A micro-lens array then divides the region into smaller images that are processed to reveal their spectral content.

Because spectral and image data are acquired in one step, this new device provides two effective indicators to detect skin cancer. Physicians can evaluate the image data while the spectral data is compared to spectra of known cancerous or healthy regions.

Multidimensional Spectrometer

UW-Madison researchers have developed a spectrometer capable of measuring multidimensional spectra in a straightforward manner. The spectrometer utilizes a pulse shaper and a simple collinear geometry so that alignment is easy and data collection can be automated. Researchers can simply insert their samples and select one of several options for collecting 2D IR spectra. With this invention, along with some engineering and computer programming, the powerful new optical techniques are ready to be commercialized in a user-friendly apparatus that will have broad appeal among researchers.

Multispectral Laser with Improved Time Division Multiplexing

UW-Madison researchers now have developed an improved, multi-wavelength, time-division multiplexed (TDM) laser capable of individually controlling multiple narrow wavelengths in separate time-division windows. Unlike the previous laser, this device uses a cavity that provides the same cavity length for each wavelength. To separate light into multiple wavelengths, it introduces a fixed time shift in the arrival of each wavelength at the output coupler as a function of the wavelength. It continuously cycles through the spectrally narrow wavelengths, spending a predetermined amount of time on each one. Specifically, the laser cavity holds the optical amplifier between a wavelength-dependent delay element (WDE) that temporally separates a multi-wavelength light pulse into discrete constituent monochromatic components, and a complementary wavelength-dependent delay element (CWDE) that temporally collects the monochromatic components after separation. This design reduces gain competition, simplifies the circuitry for controlling the amplifier and distinguishing the output pulses, and improves the consistency and control of the multiple monochromatic wavelengths.

Spectrographic Sensor for Precisely Measuring Gas Parameters in an Internal Combustion Engine

A UW-Madison researcher has developed a device capable of accurately and quantitatively measuring gas temperature and concentration within a cylinder. The device includes a fiber optic light source installed in a spark plug. The fiber optic source introduces a light signal into the combustion space within the cylinder. A high-speed spectrographic sensor, such as a spatial heterodyne spectrometer, analyzes the strength of the light after it interacts with the combustion gases. A computer can then use this information to automatically determine gas temperature and water concentration, and to measure the absorption spectra of the combustion gases.

Bright, Tunable, Continuous Wave Coherent Terahertz Source

UW-Madison researchers have developed an intense, narrow-band, tunable source of terahertz radiation. Two THz beams are produced by two pump beams via difference frequency mixing (DFM) in a second order non-linear optical material.

By encasing the optical material between two layers of dielectric cladding material, the researchers were able to dramatically decrease the amount of THz absorbed. The dielectric materials don’t absorb much THz, and provide a waveguide structure that helps confine the beam. This makes it possible for the first time to efficiently couple the exiting THz radiation to a flexible guiding structure, much like a fiber optic cable.

Continuous-Wave Laser Source for High Speed Spectroscopy

UW-Madison researchers have devised a simple and inexpensive laser-based spectroscopy approach that is similar to FTIR in principle; however, because it has no moving parts, it offers many advantages, including the ability to produce spectra every microsecond or faster. The laser is generally fashioned as a fiber laser, which is a laser cavity composed primarily of fiber optic cable. To measure spectra, the continuous-wave fiber output is directed at the test article and onto a single photoreceiver. The photoreceiver signal is then digitally processed to produce the desired spectra.

Super-Continuum Ultraviolet Light Source with Single Stage Laser Drive

UW-Madison researchers have developed a fiber-coupled, broadband UV light source with approximately one million times the spectral radiance of conventional UV lamps. This UV supercontinuum source consists of a pulsed ultraviolet laser followed by a fiber-optic cable. It produces light that is laser-like, except that it possesses many colors rather than just one. To achieve supercontinuua, a particular relationship among properties including laser pulse duration and energy, laser wavelength and fiber dispersion, diameter and length must be met.

Modeless Wavelength-Agile Laser

A UW-Madison researcher has developed an easily constructed modeless laser with a rapidly sweeping color that results in improved performance in many sensing applications. The laser changes its cavity length at a speed that prevents the formation of modes, resulting in a spectrally narrow, swept-wavelength light source that eliminates mode hopping. A pivoting mirror design provides the high rate of cavity length change.

High-Speed, Swept Frequency Spectroscopic System

A UW-Madison researcher has developed a wavelength-agile laser capable of rapidly scanning through a broad wavelength range, with superior light coupling and reduced light loss. It is particularly well suited to measure gas absorption in engines.

The invention consists of commercially available components that include an ultra-fast laser, a non-linear optical fiber and a frequency-spreading element. When these components are connected in series, the fiber optic cable receives a multi-frequency light pulse and spreads its frequency in time prior to transmitting it into a test cell. This approach significantly reduces losses involved in coupling light to the optic fiber and avoids the measurement of unwanted nonlinear processes. By directing the laser’s output through a test article of interest, the item’s properties can be determined by the recorded transmission spectrum.

Microwave Dielectric Spectroscopy Method and Device

UW-Madison researchers have developed a method of using dielectric spectroscopy to detect protein conformational changes. This alternative method relies on the fact that proteins in solution are surrounded by one or more shells of “bound” water. In response to changes in a protein’s conformation, bound water is released or rearranged, causing a change in the solution’s permittivity that can be easily measured by using this invention.

Previous dielectric spectroscopy methods have not been widely implemented because they involve complicated analysis. In this invention, data analysis is as simple as in conventional optical spectroscopy. In addition, no labeling of receptor or ligand is required for detection.

Photon-Sorting Spectroscopic Microscope System

A UW-Madison researcher has developed a novel spectroscopic microscope system that is well suited for multi-photon spectral imaging for analysis of specimens containing one or more types of fluorophores. The microscope is projected to cost a fraction of what current commercial MPELSM do because it takes advantage of new digital components and integrates the controls between many parts of the system.

New Spectrometer Tool for Studying Biomolecules and Very Thin Films

UW-Madison researchers have developed an instrument for the non-destructive study of surface and interface phenomena, as well as the properties of very thin layers. The instrument employs a near-infrared Fourier transform infrared spectrometer (FTIR) to collect reflectance spectra from a prism-gold film-thin film assembly at a well-defined angle of incidence. The measured reflectance spectra exhibit a pronounced minimum in the IR range from 700-2000 nm due to the effect of the SPR; the position of the minimum can be varied by changing the angle of incidence and the gold film thickness. A shift in wavelength of this minimum position occurs upon the adsorption of molecules onto the thin film surface, due to the change of index of refraction at the interface. The FTIR spectrometer provides high dynamic range and the wavelength stability and reproducibility required to make sensitive SPR wavelength shift measurements and broadens the spectral range over which the SPR measurements can be performed. The FT-SPR technique can be utilized for measurements ranging from sub-monolayer films to films with a thickness of about 200 nm.