Specifications

16 Chapter 4. Operation

Figure 4.1: SketchoftheMOGLabs CEL,showingthe ﬁlterrotationad-

justment screw, labelled λ.

4.2 Scanning

Theexternalcavitylengthiscontrolledbypiezoactuatorsmoving

theoutputcoupler.Thecavitylengthincreaseswithincreasingvolt-

age on the piezos,thus decreasing the laser frequency.For a large

frequencychange,thelaserwillusuallyhoptoaneighbouringcavity

mode (see Fig. 4.2).

Thecontinuous scan range (free of modehops) canbe optimised by

careful adjustmentofthe injectioncurrent,which aﬀectsthe refrac-

tiveindexofthediodesemiconductorandhencethefrequencyofthe

cavity mode.

Thisshiftofcavitymodefrequencyallowsforcompensationofthe

mismatchoftuningresponses. Thediodeinjectioncurrentcanbe