## Dither locking – generating an error signal

NOTE: The dither command is classed as an experimental feature in Finesse v2 A quick example for generating an error signal by dithering the mirror. For this we need to use the dither command. dither component_name f m order phase Where f and m are the dither frequency and modulation index. The first simple example […]

## Quantum noise source breakdown

The quantum noise that limits the sensitivity of a detector can have multiple sources. The main contributor is usually the vacuum noise that enters into the interferometer from the dark or also known as the AS (Anti-Symmetric) port. More generally, vacuum noise will leak into the detector wherever there is an optical loss – which […]

## Shift and phase change from tilted beamsplitters – part 2: finesse examples

Introduction This is the second post discussing the shift and phase dependence of a beam going through a z-shaped telescope setup when both beamsplitters are tilted over a small angle β. The first post (part 1: theory) derived both the shift in the position of the beam and the change in phase at the detector […]

## Shift and phase change from tilted beamsplitters – part 1: theory

Introduction Given a z-shaped telescope setup with two beamsplitters such as depicted in Fig. 1, we calculate the effects on the outgoing beam when applying a small additional tilt β to the angle of incidence α of both beamsplitters. Such a small extra tilt is applied in Finesse 2 via the xbeta parameter of a […]

## Computing modal scattering coefficients

When doing optical modal modelling you will at some point have to consider how some incident mode gets scattered by some deformation or effect into another mode. There is a lot of math to take in before you start calculating stuff but there is a good review of it all here: https://link.springer.com/article/10.1007/s41114-016-0002-8#Sec118 The computational problem […]