LM-0100 Michelson Laser Interferometer

Topics:

  • Green DPSSL as coherent source

  • Properties of laser radiation

  • Adjustable Beam Expander

  • Two beam interference

  • Fringe contrast

  • Coherence length

  • Fringe detection

  • Spherical and plane waves

  • Optional two mode HeNe laser


LM-0100 Michelson Laser Interferometer

Michelson Interferometer with two mode HeNe Laser

Already in 1881 A. A. Michelson constructed an interferometer, which later on also got his name, to counter prove successfully the theory of an universal ether assumed to be existing at that time. Later on he determined with this set-up the length of the basic meter in units of light wavelengths. Still, the promising use of interferometers in performing high precision length measurements only reached significance after the discovery of the laser as a coherent light source.
Today this contact less working high precision length measuring instruments have become an important tool for many areas of the machine building, industry like adjustment, final control, incremental displacement measurement for CNC machines, the control of machine tools and for calibration procedures.
With the newest laser interferometers resolutions up to the nanometer range can be realized. The arrangement of the optical components has changed with regard to the original Michelson interferometer by the use of lasers as light sources. But with some exceptions generally the two beam arrangements of Michelson is used.
Within the frame of this experiment first the classical interferometer is setup and the interference pattern are observed on a screen. To understand the observed interference pattern the properties of Gaussian beams, wave fronts, radii of curvature and the superimposition of waves are discussed in the theoretical part of the manual. Starting with a simple model of monochromatic radiation, the spectral bandwidth of a light source will be considered and the influence on the contrast of the interferometer discussed. The coherence length is introduced, defined and measured.
The applied HeNe-Laser emits two orthogonally polarized modes with a coherence length of about 18 cm. In a second step the Michelson setup is upgraded to an technical interferometer.

Classical Michelson Interferometer

Principle set-up of the Michelson interferometer Measuring the contrast function
A. Classical Michelson Set-up B. Measuring the contrast function

The classical Michelson setup consists of the beam splitter, the mirror 1 and the mirror 2. The incident beam from a laser is expanded and split into two beams at the beam splitter (BSP). The returning beams from mirror 1 and 2 are imaged by means of a diverging lens onto a translucent screen. Mirror 2 is mounted on a translation stage. The expansion lens provides an enlarged beam with plane or curved wave fronts resulting in a fringe pattern with a parallel or circular pattern.
LM-0100 Michelson Laser Interferometer, consisting of:
Item Code Qty. Description
1 CA-0080 1 Optics cleaning set
2 CA-0450 1 BNC connection cable 1 m
3 DC-0040 1 Diode laser controller MK1
4 LQ-0040 1 Green (532 nm) stabilized Laser, 40 mW
5 MM-0020 2 Mounting plate C25 on carrier MG20
6 MM-0100 1 Target Cross in C25 Mount
7 MM-0110 1 Translucent screen on carrier MG20
8 MM-0440 1 Kinematic mount ø25.4 mm on MG20, left
9 MM-0444 1 Kinematic mount 1", translation stage on MG65
10 MP-0050 1 Cross-piece MG-65 with kinematic mount ø 25mm
11 MP-0130 2 Optical Bench MG-65, 300 mm
12 MP-0150 1 Optical Bench MG-65, 500 mm
13 OC-0010 1 Biconcave lens f=-10 mm, C25 mount
14 OC-0380 1 Beam expander x8 in ø 25 mm housing
15 OC-0500 1 Beam splitter plate ø 25 mount
16 OC-1200 2 Laser mirror C30, ROC flat, HR @ 632 nm
17 UM-LM01 1 Manual Michelson Interferometer
Option (order separately)
18 CA-0200 1 Oscilloscope 100 MHz digital, two channel
19 LM-0110 1 Two mode HeNe laser extension for LM-0100
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