Support Topics

How do I use LightField to do absorbance measurements? [+][-]

Q: How do I use LightField to do absorbance measurements?

A: On-line absorbance measurements are easy to perform within LightField using the following steps.

  1. Select “Regions of Interest” and then set up two Custom Regions of Interest that are equal in size.
  2. Under "Online Processes", check Apply Formula and then select Edit Formula

    online process
  3. Under “Pre-Defined Formulas”, select Absorbance.
    predefined formulas

  4. LightField will automatically select ROI 1 as the reference channel and ROI 2 as the transmitted channel. You can reverse these channels if necessary.
  5. The output will be Log10(reference/transmitted)

  6. Run or Acquire data

  7. For these measurements we suggest that you acquire a new background reference (Online Corrections) and also use a shutter during acquisition.


How do I align and focus my spectrometer? [+][-]

Q: How do I align and focus my spectrometer? (IsoPlane 160 and SpectraPro spectrometers only)

A:  First: Focus spectrometer

  1. Set the center wavelength to a peak wavelength of your light source. Alternately, if you have a source you image regularly, use that and set the spectrometer to imaging mode.
  2. Adjust the focusing knob until the peak’s spectral width is as narrow as it can be.  As you adjust the focusing knob, the spectral width should shrink and then expand, this is moving through focus.  If you are using imaging mode, you should see the image become less blurry, then sharp, and then blurry.
  3. If when moving the knob, you do not see this, i.e. the spectral width only shrinks or increases, focus is beyond reach of the focusing knob.  You will need to add or remove a spacer.

Second:  Rotational alignment

  1. Make sure the computer interface cables (for the spectrograph and detector) are connected.
  2. Verify that the power supplies are plugged into an AC source and are connected to the spectrograph and detector.
  3. Turn on the power to the spectrograph and the detector.
  4. Start the application software.
  5. Loosen the rotation adjustment screws enough that you can rotate the detector. The mounting plate holes are slotted to allow about 4° of rotational positioning.
  6. If background subtraction is an available function, acquire a background to be applied while data are acquired.
  7. Turn on the light source.
  8. Put the spectrometer into imaging mode by setting the center wavelength to 0nm.
  9. Open the slit so that visible light is coming through the spectrometer and is visible on the detector (you will see narrow rectangle of light).
  10. While viewing the data being acquired, rotate the detector until the long side of the rectangle is parallel to the short edge of the detector area (it may be helpful to use the cursor to aid in alignment).
  11. Tighten the mounting screws.



How do I normalize my data? [+][-]

Q: How do I normalize data?

A: To normalize intensity, use the following formula:

output=input/reduce(input, maximum)

This formula scales the data so the highest peak is normalized to one.

This can be applied during acquisition under Online Processes, or in post processing under Processes - Formula

normalize data

IMPORTANT: Do not use normalization during live acquisition when running step and glue because it will normalize every frame as acquired resulting in mismatches between the spectral data when it is stitched together.


How should I select external optics to bring light into my spectrometer? [+][-]

Q: Can you provide some information on selecting external optics to bring the light into my spectrometer?

A: Below are some comments on lens selection.

Make sure the lenses are optimized for transmission over the full wavelength region of interest. For example, some lenses are optimized for visible wavelengths so the AR-coatings are not optimized for NIR wavelengths.

Wavelength Range:
The range specified is 550-920nm.

Make sure the lenses are chromatically-corrected for the wavelength region of interest. You don’t want a large change in focus at different wavelengths.

Spectrometer Aperture (f/#):
Make sure you don’t overfill the optics. This will only contribute to potential stray light. If anything, it is okay to slightly under fill the optical system.

If the lens has an integrated f-stop, the lens iris can be adjusted to match the spectrometer.

In some instances it might be a good idea to use a lens pair to accomplish the object-image transfer from the sample to slit.

The first lens collects and collimates light from the sample.
The second lens takes the collimated beam and focus this on the slit.
We normally recommend a 1:1 lens arrangement (equal focal lengths), however this could be changed if required to optimize the light collection. For example, collect at f/2 from a fiber and focus at f/4 to match the spectrometer.



What are the damage thresholds of the internal optics and gratings in my Princeton Instruments spectrometer? [+][-]

Q: What are the damage thresholds of the internal optics and gratings in my Princeton Instruments spectrometer?

A. The laser damage threshold number we have for the spectrometer coatings (#1900 Al+MgF2) is approximately 500mj/cm2, 10-20Hz operation, 20ns pulses. This equals ~5-10 W/cm2.

 NOTE: These were only tested at UV wavelengths. We do not have damage threshold information above 400 nm at this time. As a reference,  damage thresholds are higher for longer wavelengths.

I need help to calculate this resolution [+][-]

Q: I need help to calculate this resolution.

From the Princeton Instruments’ grating calculator it shows 0.465nm with 20um slit. But from my calculation, it should be 0.106nm x 2.5=0.265nm, which is correct?  I don't know how to calculate the 0.465nm. If I use 100um slit, the resolution is 5 multiply the resolution of 20um slit?

A: To calculate resolution (bandpass) with a slit width opening of 100um or wider, multiply dispersion X slit width. Example: If the dispersion is 7.836nm/mm and the slit width is 100um, then the calculation is 0.1mm x 7.836 = 0.7836nm.

For slit widths less than 100um, there are other factors such as residual optical aberrations that contribute to the bandwidth (FWHM). When using a CCD with 20um pixels (Pixis-400), the calculator assumes that it takes 3 pixels to form a spectral line. With the Pixis 2K with 13.5um pixels, this would be 4.44pixels (20/13.5 * 3  = 4.44).

The grating dispersion calculator assumes 4.44 pixels (60um) FWHM when it calculates CCD resolution, so if the dispersion is 7.836nm/mm, then the calculation is 0.06 x 7.836 = 0.470nm. You can also calculate this by multiplying the FWHM in pixels by the dispersion/pixel, or 4.44 X 0.106 = 0.470nm. The calculator shows 0.468nm vs. my calculation of 0.470nm, which is probably due to rounding.

Go to the Grating Dispersion Calcuator on the website for addition information.

NOTE: I believe this is conservative and that the real FWHM under these conditions will be most likely be closer to 2.5 pixels (50um) with a Pixis-400, or 3.7 pixels (50um) with a Pixis 2K. For the Pixis 2K, if you multiply 0.05 x 7.836, the resulting resolution will be 0.392nm. Or, 3.7pixels FWHM * 0.106nm/pixel = 0.392nm


Are other gratings available? [+][-]

Q: Are other gratings available for my spectrometer that are not listed on your website?

A: If you require a different grating than is available on the product web page, please contact your sales engineer to determine a custom grating that will best meet your requirement.

Optional Display of Wavelength Calibration from Images [+][-]

As an option, you can display a cross-section (spectra or graph) of your recently acquired image without synchronizing files. Simply follow these following three steps.


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