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Frequently Asked QuestionsWhat is "1-point" KestrelCalTM calibration?The "1-point" calibration method is used with scanning spectrographs that have stepper motor control in our KestrelSpec software. Currently supported spectrographs include Spectral Products (formerly CVI Laser), Bruker Optics (formerly CHROMEX) and the SpectraPro by Acton Research. To calibrate a scanning spectrograph, the KestrelSpec software uses a single known wavelength and spectrograph parameters such as grating groove density, total included angle, focal length and CCD pixel size. To perform the calibration, the user first sets the spectrograph to a wavelength that corresponds to the most prominent line (brightest peak) in the field of view in the CCD image. It is recommended that Hg be used as a light source during the "1-point" calibration process and the spectrograph be set to the known wavelength of the most prominent Hg peak in the field of view. As an alternative, any light source can be used with the spectrograph set to 0 nm, which is known as a "white light" calibration. Once the spectrograph is set to the wavelength of the brightest line in the CCD image, the user clicks on the AutoCal button in the control palette of the KestrelSpec software. The calibration procedure will then find the center-of-focus pixel that corresponds to the single known wavelength of the most prominent peak in the field of view. Once the "1-point" calibration is successful, each acquired spectral curve will be accurately calibrated in either nm or Raman cm-1 units, even when the wavelength setting of the spectrograph is changed. What is "2-point" KestrelCalTM calibration?The "2-point" calibration method was developed exclusively by Catalina Scientific for use with the SE 200 echelle-type spectrograph built by Optomechanics Research. To calibrate an SE 200, an Hg image is first acquired and any two prominent Hg peaks are selected for the 2-point calibration. KestrelSpec has a Peak Finder tool for images to aid in determining the location of prominent peaks. Below is an example of an Hg echelle image with the prominent peaks labeled: ![]() The X and Y coordinates of two prominent Hg peaks are entered in the calibration dialog box, which in this example are 546.074nm and 579.066nm for an SE 200 spectrograph: ![]() The user then clicks on the Calibrate X Axis button and KestrelSpec calculates the calibration parameters that will be used in the creation of spectral curves from acquired images. Once the "2-point" procedure is successful, each acquired spectral curve will be accurately calibrated in either nm or Raman cm-1 units. What is "3-point" KestrelCalTM calibration?The "3-point" calibration method was developed exclusively by Catalina Scientific for use with the EMU-120/65 echelle spectrograph that we design and build. To calibrate the EMU-120/65 spectrograph, an Hg/Ar image is first acquired and three prominent Hg and Ar peaks are selected for the 3-point calibration. KestrelSpec has a Peak Finder tool for images to aid in determining the location of prominent peaks. Below is an example of an Hg/Ar echelle image acquired with the EMU-120/65 with the prominent peaks labeled: ![]() The X and Y coordinates of three prominent Hg and Ar peaks are entered in the calibration dialog box, which in this example are two Hg peaks at 253.652nm and an Ar peak at 811.531nm: The user then clicks on the Calibrate X Axis button and KestrelSpec calculates the calibration parameters that will be used in the creation of spectral curves from acquired images. Once the "3-point" procedure is successful, each acquired spectral curve will be accurately calibrated in either nm or Raman cm-1 units. What is KestrelTempTM temperature calibration?In the full version of the KestrelSpec software, there is an option to acquire and display spectral curves in Temperature Mode. KestrelTempTM is a method of calculating the unknown temperature of spectral data once a temperature reference curve, with a known temperature, has been defined. This known temperature reference curve and any unknown sample curve are then transformed by a proprietary algorithm to produce a linear function of relative intensity versus frequency (Omega). The temperature of the unknown source can then be calculated from the slope of this relationship between relative intensity and frequency. The software calculates a least squares fit to the function and determines the temperature of the unknown source including a 1 sigma error coefficient. The accuracy of the temperature calculation can be optimized by adjusting the spectral range over which the least squares fit is operating. The better the fit, the smaller the temperature error estimate. In the sample temperature spectra below, a reference spectrum was acquired from 330nm to 1050nm using a black body source at 6 volts with a known temperature of 3200K. Three subsequent spectra of unknown temperature were then acquired covering the same 330nm to 1050nm range using the black body source at 5, 3 and 1 volts. The curves below show the relative intensity versus frequency and the calculated temperature and error estimate for each of the unknown samples: ![]() |
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