Wavelength of a Laser - eol

Subject Focus:
High school physics or
optics/photonics course
Materials & Preparation
Time:
One to two class periods
Carbon, Climate, and Laser Technology
Teacher’s Guide
Teacher and Student
Materials:
• He-Ne Laser
• 2 diffraction grating slides
with known grating widths
(each w/ different widths)
• a screen to project upon
(a white box works well)
• measurement tools
• student data recording
form (optional as recording
in lab notebook may be
preferred)
Wavelength of Laser Light
National Science Content Standards Addressed:
National Science Content Standards A, E, and G
• www.atd.ucar.edu/apol/biocomplexity
• www.eo.ucar.edu
Learning Ojbectives:
Students will determine the wavelength of a helium neon laser. Students will collect
six different sets of measurements in this experiment and use these measurements to
solve for the wavelength of the laser.
Preparations:
Put out one or sets of a laser, screen and two diffraction gratings for student use.
The intent is to have the laser beam pass through a diffraction grating resuling in
an interference pattern on the screen. Either the screen or the grating will need
to be movable since each grating will be used three times at different distances
from the screen. Decide ahead of time which object will be moveable. Each
of the three distances should yield a clearly observable interference pattern.
The photos on the following page show visual representations of the materials,
setup, and interference patterns generated during the experiment. A graphic of
the electromagnetic spectrum with wavelengths specified is also shown.
Procedure:
Have students record the diffraction grating lines (mm) and convert them into
centimeters to determine the slit width (d). Students will also record the distance
from grating to screen (L) and distance from a maximum bright spot to an
adjacent maximum bright spot (x). Two different gratings are to be used at three
different distances from the screen and measurements recorded. Students will
then use these measurements to determine the wavelength of the laser.
Connection to APOL Biocomplexity Project:
Lasers are of many wavelengths and each type of laser has a particular application
based on that wavelength. The lasers used in the APOL project are designed
to give a final output of 4.3 x10-6 meters. This is in the mid-infrared range and
is invisible to the eye. In this activity, a laser that has an output visible to the
eye will be necessary. The He-Ne laser is the most common type of laser in the
school environment.
Solution:
Most schools will use a standard red helium neon laser. The wavelength for this
laser is 633 nanometers. Some schools may have access to helium neon lasers of
different wavelengths. The results for those lasers should be as follows: Green:
543.5 nm, Orange: 612 nm, and yellow: 594 nm.

grating
Grating in position in from of laser
Laser, grating, and screen
Laser, grat ing, an d screen
Gra ting in po sition in from of laser
Laser, 300 lines/mm grating, and screen
Electromagnetic Spectrum
Laser and two gratings
Laser, 300 lines/mm grating, and screen
Pattern generated by laser and 300 lines/mm grating
Photos by Randal Albrandt
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Diffraction Grating
(lines/mm)
Slit Width (d)
(cm/line)
Two different gratings must be used three times each.
Distance from
grating to screen (L)
(cm)
Distance from
maximum to
maximum (x)
Note that x can be measured from any bright spot to the adjacent bright spot. Also, the diffraction gratings are
in lines per mm. This must be converted to cm per line. This value corresponds to d in Diagram A.
To determine the wavelength of the laser:
( x )( d)
λ =
Use the values of x, d, and L from your data table and the double slit formula L to determine
the wavelength of the laser. Average your six computed values and determine a final average for the wavelength
of the laser.
Show all
substitutions
of
data into
formula
Final Value
(cm)
Final value
(microns)
( x )( d)
λ =
L
( x )( d)
λ =
L
Wavelength of Laser Light
Student Data Form
( x )( d)
λ =
L
( x )( d)
λ =
L
( x )( d)
λ =
L
( x )( d)
λ =
L
Average
Wavelength
Ask your teacher to provide you with the actual wavelength of the laser used in your experiment. Compare this
value with your experimental value. Discuss any aspects of the experiment that would explain any disagreement
with the actual value.
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Diagram A
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