a0de5644f1d641160beb44ee5fc6ff59.pdfPage 1 of 3Last Modified 11/20/06LAB 12 - CHARACTERIZATION OF LIGHT SOURCES Physical Sciences VersionI. IntroductionLight sources can be characterized according to their wavelength spectrum as either narrow or broad-banded. For example, atomic resonance lamps such as sodium or mercury emit light only at certain wavelengths. The spectral bandwidth of the light at each atomic line is generally very narrow. Lasers, of course, are effectively monochromatic (i.e. single wavelength). Conversely, arc lamps, such as xenon, emit over a very broad wavelength range with few spectral features. The choice of source type depends on the particular application as well as the availability of optical components such as filters and spectrometers. In this experiment, you will verify the wavelength calibration of a spectrometer with a known narrow wavelength source (Mercury Arc Lamp). Then, you will characterize the laser wavelength linewidth of the He-Ne laser. Lastly, you will measure the transmission of a dye over the visible range.II. ObjectivesCalibrate a grating spectrometer with known wavelength light sources.Measure line width of He-Ne laserObtain visible light transmission of a dye.III. ProcedureThe suggested overall layout for this experiment is given in the figure. The major components include: spectrometer, light source and lenses. III.1 Spectrometer Calibration (Atomic Emission Lamp)1) Assemble the basic system layout as per Figure 1.Figure 1: Experimental setup for measuring spectra of a lamp.2) Use the mercury lamp for calibration. Your goal is to collect and collimate some of the light with a lens. A second lens focuses the light onto the spectrometer entrance slit. Initially, remove the array detector from the spectrometer. This will enable you to open the top of the spectrometer and observe the propagation of light in the spectrometer.a0de5644f1d641160beb44ee5fc6ff59.pdfPage 2 of 3Last Modified 11/20/063) Use two lenses of equal focal length. The focal length should be about 100mm. Place the first lens a focal length away from the lamp. This placement should collimate some of the light from the lamp. Place the second lens a focal length away from the slit. Allow approximately 10 inches in between the two lenses for placement of the dye sample. Use initially a slit width of about 1mm or less. The image should be focused at the slit. Align the spectrometer/slit, lenses, and lamp so that they are collinear and at the same height. Open the top of the spectrometer. Using another index card, follow the light beam around in the spectrometer. The system is properly aligned when the light through the entrance slit is centered on the first curved mirror. If you have difficulty seeing the lamp light in the spectrometer, you can temporarily remove the slit and dim the room lights. 4) Using the adjustment caliber that rotates the grating, adjust the rotation of the grating until you see the RED spectral line emerging roughly from the center of the spectrometers exit. 4) Close and seal the top of the spectrometer. Place the detector array in the spectrometer. Replace the slit if it was removed. Turn on the control box for the spectrometer.6) Initiate the software program to run the spectrometer: (a)On the computer, open up the Start menu. (b)Look for KestrelSpec SBIG (it should be right there on the DESKTOP or go into All Programs); open it. (c) Click OK when the SBIG CCD Cameras window comes up. (d)Under the SETUPAcquire tab, adjust the acquisition time to 0.01 seconds (the default is 0.1sec)7) To acquire a spectral image (take a picture from the spectrometer), go to the ACQUIRE tab and drop down to Acquire Spectra. On the computer display, you will observe a plot of PIXEL COUNT on the y axis and PIXEL NUMBER on the x-axis. The PIXEL COUNT is proportional to the intensity of the detected light. The PIXEL NUMBER can be converted to a wavelength using the calibration procedure below.8) If the detector array is saturated, you will need to attenuate the light into the spectrometer. You can do this either my lowing the Acquisition time (under SETUPAcquire tab) or by inserting neutral density filters. After you make adjustments to ensure that the detector array is not saturated, you can calibrate the spectrometer. Using the calibration chart for the lamp that you are using, identify for the computer the wavelength values for several of the peaks. The computer will use these values to calibrate the spectrometer. On the plot, there will be a black dot somewhere along the red line. This is a movable cursor that will enable you to read off the x and y coordinates of a data point. Click on that dot and move to the peaks in the graph. For at least two of the peaks, record the corresponding amplitude and pixel number. For the Mercury lamp, the red calibration line is 615.0nm. 9) Now you have the calibration points to calibrate the wavelength scale