Available Photonics Experiments:

P5835 Spectral analysis PDF Download page

  • Principle of gratings
  • Reflection grating
  • Spectrograph
  • Czerny-Turner monochromator
  • Measuring wavelength
  • Spectral resolution
  • Examples of investigations and measurements
General setup
The spectrometer is formed by the adjustable entrance (S1) and exit (S2) slits, the rotary grating (G1) and the two spherical mirrors M1 and M2. Behind the exit slit (S2) a lens with protective tube (3) images the slit (S2) onto the photodetector (5). The intensity is determined by measuring the photo current of the photodiode by means of the digital multimeter.
The grating is mounted onto a rotary unit which allows the precise rotation of the grating. The provided scale informs about the angle and is a measure for the selected wavelength. The scale is calibrated by using the known wavelength of the spectral lamp (7). This measurement shows the sinusoidal relation between the angle and the wavelength. The setup shown in the figure on the right represents a spectrometer for separating a specific wavelength of a light source (6) and measuring its intensity. Such a setup is also known as Czerny-Turner arrangement.
Grating spectrograph and monochromator
A spectrograph can also be used to characterise the spectral properties of a probe or optical filter which is inserted into the beam path of the spectrometer. A light source (7) providing the required wavelength range is placed to the entry slit of the spectrometer. Firstly the spectrum without the probe is recorded. After this, the same measurements are repeated however with the probe. The plot of the intensity versus the wavelength is normalized with the data measured without probe. Within this series of measurements also the influence of the slit width on the spectral resolution is investigated.
White light LED
The white light source (10) consists of a high brightness LED. The spectrum of the lamp is shown in the figure on the left.. Beside a peak at 440 nm a broad range from 500 to 700 nm is available.
The light source is connected to the adaptive power supply (9) which allows the variation of the injection current and that way the intensity of the emitted light.
The divergent radiation is collimated by means of a lens (3) having a focal length of 40 mm.
Spectral lamp
The spectral lamp contains a modern energy saving lamp with integrated 220 VAC power supply and emits a spectrum as shown on the right.
The spectral lamp is used in connection with the set of gratings to analyse the effect of the grating constant with respect to the resolution of a line spectrum.
  • P5835 Spectral Analysis consisting of:
14A-04121Absorbtion Filter
24B-00401Plano-convex lens f=40 mm, C25 mount
34B-00701Planoconvex lens f=20 mm, click 25, attached light tube
4ED-00101Adaptive power supply APS-05
5ED-02101PIN Photodetector, BPX61 with connection leads
6LS-00101LED white C25
7LS-00901Spectral lamp with slit and power supply
8MC-01121Screen 80 x 40 mm, horizontal and vertical scale
9MC-02602Optical rail MG 65, 500 mm
10TP-00301Digital multimeter 3 1/2 digits
11XM-01901Plate holder on carrier 20
12XM-07701Spectrometer mirror assembly
13XM-07801Spectrometer grating assembly with two gratings
14XM-10903Mounting plate C25 with carrier 20 mm
15XM-11101Adjustment holder, 4 axes, carrier 20 mm