Datasheet

CHAPTER 2. ELECTRICAL AND OPTICAL PROPERTIES 10
Is it possible to reduce the divergence?
The divergence in the vertical direction is a parameter that is governed by the thickness
of the laser waveguide. It is high because the waveguide is narrow. Reducing the
divergence would impair the performances of the laser. Moreover this modification
would need tremendous development effort and it would be necessary to compromise
on the power and operation temperature.
2.3.2 What is the polarisation of the emitted mode?
The polarisation is vertical if the laser is laying horizontally, i.e the electrical field is
perpendicular to the plane formed by the ceramic pads, see (Axes of lasers). It is
very pure as there is a quantum mechanical selection rule forbidding emission in the
horizontal direction.
2.3.3 How do I collimate the beam?
Due to the large divergence of the beam, it is recommended to use fast optics (f/1 . . .
f/0.8) to collect most of the emitted light. We recommend the lens system from Cascade
Technologies (see http://www.cascade-technologies.com), and aspheres from Janos
(see http://www.janostech.com) or Optical solutions (see http://www.opticalsolutionsinc.com).
2.3.4 How do I calculate the radiance?
The radiance can be estimated in two ways:
• Supposing the laser is emitting monomode transversal and ideal optics for a gaus-
sian 00-beam apply, the radiance is then given by B = 4 × P/(λ
2
), with P the op-
tical output power and λ the wavelength of the laser.
• Using standard values (which can vary for up to factors of 2 between lasers),
the aperture A is in the range of 0.03mm by 0.005mm, and the illuminated solid
angle (for 60deg vertical and 20deg horizontal divergence) W is in the range of
0.3 (or 2 × π × 0.045), and therefore the radiance B = P/A/W or approximately
B = P/(4e − 5mm
2
).
These are highly approximative values; if you need well defined ones, ask for the
needed values for a specific laser you are interested in.