Lab 4 Laser - Institutt for elektronikk og telekommunikasjon - NTNU

1.3 Lab exercises 10
1.3 Lab exercises
1.3.1 Equipment
Welding glasses for eye protection
HeNe one-brewster discharge tube
High Voltage(1900 V) power supply
Alden cable with ballast resistor
Output coupler-mirror (OC)99%@632.8nm
Power meter
Polarizer
Quarter wave plate
Chopper
Photo diode with amplifier
Oscilloscope
1.3.2 HeNe-tube
The HeNe-tube is mounted in a stand with the electrical wires attached. Do
NOT touch any of this. The tube is very fragile and easy to break!
Plug the 220V power supply unit into the wall socket and wait for the tube to
ignite.
Describe the color of the light that is emitted. And measure the output power
from the tube with the power meter.
1.3.3 HeNe-laser alignment
Put the mirror onto the rail and put it 1 cm from the brewster-window. Observe
the change of light color that is transmitted through the mirror. Why does the
light have this color? Measure the power emitted.
Now try to align the mirror so that the light gets reflected off the mirror and
back through the brewster mirror so that lasing is obtained. Measure the power
emitted from the laser at once when lasing is obtained. It is quite easy to see,
because a flash of red light will occur when lasing starts.
What is the µm readings when lasing starts? What is the effect when lasing
starts? What is the maximum power that you can get out of this tube? What
is the corresponding µm readings?
Try to slide the mirror away from the tube. Measure and see how far you can
slide while maintaining lasing. Plot the power of emitted radiation vs. length
of the tube. Be careful and don’t touch the anode of the tube (High voltage)!!
1.3.4 Transversal modes
Look at the mode picture projected at the wall (use a sheet of paper to get a
better mode picture). Which TEM mode is this? Use a lens to inflate the mode
picture if it is difficult to see. What happens when the mirror is or tilted back
and forth? Why?