Principle

The difference between spontaneous and stimulated emission of
light is demonstrated. The beam propagation within the resonator
cavity of a He-Ne laser and its divergence are determined, its
stability criterion is checked and the relative output power of the
laser is measured as a function of the tube’s position inside the
resonator and of the tube current. The following items can be
realised with advanced set 08656-02. By means of a birefringent
tuner and a Littrow prism different wavelengths can be selected and
quantitatively determined if a monochromator is available. Finally
you can demonstrate the existence of longitudinal modes and the
gain profile of the He-Ne laser provided an analysing Fabry Perot
system is at your disposal.

Benefits


set up and run a laser, that is by now classic, from its constituting elements

get a feel for the delicate adjustments necessary to achieve lasing conditions

dicover the way many parameters can influence the output of this gas laser



Tasks


Set up the He-Ne laser. Adjust the resonator mirrors by use of
the pilot laser (left mirror: VIS, HR, plane; right mirror: VIS,
HR, R = 700 mm).

Check on the stability condition of a hemispherical
resonator.

Measure the integral relative output power as a function of the
laser tube’s position within the hemispherical resonator.

Measure the beam diameter within the hemispherical resonator
right and left of the laser tube.

Determine the divergence of the laser beam.

Measure the integral relative output power as a function of the
tube current.


The He-Ne laser can be tuned using a BFT or a LTP. Longitudinal
modes can be observed by use of a Fabry Perot Etalon of low
finesse. Remark: These points can only be covered quantitatively if
a monochromator and an analysing Fabry Perot system are
available.

What you can learn about


Spontaneous and stimulated light emission

Inversion

Collision of second type

Gas discharge tube

Resonator cavity

Transverse and longitudinal resonator modes

Birefringence

Brewster angle

Littrow prism

Fabry Perot Etalon