KAGRA MIR (Absorption)
ManuelMarchio - 10:48, Thursday 09 August 2018 (939)
Preliminar design of the pump size reduction

I order to reduce the size of the pump and keep the waist on the same position we should add a diverging lens before the converging one.

We designed a configuration on Jammt using a -100 lens and a +100 lens. See the attached image.

The new pump size will be 37.6um (radius).

A more precise design will be after a better characterization of the pump beam profile before the lenses

Images attached to this report
939_20180809034739_reducepumpsize.png
Comments related to this report
ManuelMarchio - 15:21, Friday 10 August 2018 (942)

I made a measurement of the pump beam profile to make sure of the parameters without the last converging lens.
Result:
waist = 500um
waist position = -1m

the axis origin is the converging lens mount.

Then I updated the Jammt design using these parameters for the initial beam.
The current converging lens is f=150mm, so Jammt gives a resulting waist of 67um at 165mm from the lens. See figure. 

I also made a measurement and fit after putting back the lens. the fit gives a waist of 70um at 171mm. Quite comparable with the jammt result.

then I updated the configuration to have a pump size of 70 - 75um (diameter).
See the diagram.

I need a diverging lens f=-125mm and a converging lens f=100mm