Wisconsin Alumni Research Foundation

Analytical Instrumentation, Methods & Materials
Analytical Instrumentation Methods Materials
Multi-Spectral Laser with Periodically Poled Crystal Mixer for Carbon Isotope Ratio Measurements
WARF: P09016US

Inventors: Scott Sanders

The Wisconsin Alumni Research Foundation (WARF) is seeking commercial partners interested in developing a technique that uses a periodically poled crystal and three lasers to create a mid- to far-infrared multi-spectral laser light source.
Spectrometry is an analysis technique in which certain frequencies of light, relating to the absorption lines of a chemical species, are used to determine the chemical’s properties.  Some measurements involve determining ratios of particular isotopes, so a light source that can provide multiple precise frequencies is desirable.  Lasers can produce the desired frequencies, but only in the near infrared range (1 to 1.5 µm) rather than the middle infrared range (2 to 8 µm) needed for many applications.

One way to alter the frequencies is to incorporate a mixer, such as a periodically poled crystal like periodically poled lithium niobate (PPLN).  However, to convert high frequency laser light into lower frequency laser light, a separate laser must be applied along the axis of the periodically poled crystal.  The lasers must be controlled to be within the operating point of the crystal, but the operating point may be adjusted slightly by varying the crystal’s temperature. 

Some spectrographic applications, such as the measuring of isotope ratios, require two precisely tuned, mid- or far-infrared light outputs.  In this case, two crystals and four lasers are required.  Each laser must be designed to a specific frequency, which can be very expensive.

Recent developments have shown that the operating point of a single crystal is sufficient to allow for the slight modulation of one of the lasers to measure the isotope ratio.  This simplifies instrument construction from two crystals and four lasers to one crystal and two lasers.  However, the limited modulation range requires knowledge of the sample temperature within 100 micro Kelvin, which is extremely difficult.
The Invention
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. 
  • Laser spectrometry
  • Carbon isotope ratio measurements
  • Bacterial and viral disease identification
  • Mixing of near-infrared light to produce mid- to far-infrared light
Key Benefits
  • Requires less equipment
  • Reduces cost
  • Uses readily available lasers
  • Eliminates need to precisely measure sample temperature
Additional Information
For More Information About the Inventors
For current licensing status, please contact Michael Carey at [javascript protected email address] or 608-960-9867