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Laser Diodes: Astigmatism (As) and Precautions for Using LD

The apparent focal position of the laser diode junction is different in the vertical direction and the horizontal direction. The distance between these two foci is defined as astigmatic difference (As).

What is Astigmatism (As)?

The apparent focal position of the laser diode junction is different in the vertical direction and the horizontal direction. The distance between these two foci is defined as astigmatic difference (As).

Astigmatism (As): Measurement Method

Astigmatism through[图1]Knife edge measurement shown.

The beam of the semiconductor laser is cut off from one side with a knife edge.


[图1]

The integral value of the laser beam can be obtained by plotting the amount of light passing through the edge and the position (X) of the edge.[图2]


[图2]

By differentiating it, the beam diameter (full angle at half value) can be measured.[图3]


[图3]

Move the end face position (Z) of the semiconductor laser to measure the beam diameter.

Plot the beam diameter and end face position in each direction perpendicular to the bonding direction of the semiconductor laser and horizontal.[图4]

The astigmatic difference can be obtained from the position of the minimum value of the two beam diameters.


[图4]

LD usage precautions

1) Since the ESD level is very low compared to other discrete products, if a surge is added to the forward direction, excessive light will be emitted, the end face will be damaged, and the laser will not be able to oscillate.

ESD: Abbreviation for Electro Static Discharge, which means electrostatic discharge.

2) When using, please do not touch the end surface that functions as a lens.

(Other discrete products can often use the end face as a “cutting allowance”.)

The Links:   FS75R12KS4 MG75H2CL1