## 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 […]

## Using parakat to speed up 2D Finesse runs

A more complex/realistic example demonstrating how parakat can be used to speed up 2-dimentional simulations is provided at the end of this post. The example Finesse code used in Parallelising Finesse 2 + PyKat: three ways is deliberately simple and quick so we can demonstrate some basic functionality. However it’s not a situation you’d realistically […]

## 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 […]

## Parallelising Finesse 2 + PyKat: three ways

Occasionally you might encounter a situation where you need to run the same simulation lots of times with slightly different configurations. In cases where this also involves computationally expensive things (many orders of higher order modes, very high resolution axes, lock commands, maps,…), that can get quite tedious and you might wonder if you can […]

## Mirror reflection and transmission

The following shows a simple example for a Finesse simulation, including the text input file, a brief explanation and the resulting plot. This example has been used in the review article Interferometer Techniques for Gravitational-Wave Detection (see section 2) and is meant to introduce some of the syntax an use pattern of Finesse. We use […]

Andreas asked me for a couple of plots for the Finesse home page: http://www.gwoptics.org/I have dug up a few plots, as well as made a .svg diagram of the Advanced LIGO interferometer. Proposed Advanced LIGO diagram for the landing page: https://logbooks.ifosim.org/pykat/wp-content/uploads/sites/4/2020/06/full_ifo.svg https://ccahilla.github.io/ward_vs_finesse_DARM_model.svgThe above plot has an interactive legend, but I could not embed that functionality […]

## Fabry-Perot cavity stability for a fixed waist at the input

This simple example shows how one can use Finesse to compute quantities like the stability of a Fabry-Perot cavity whilst scanning over the cavity length but keeping the waist size fixed at the input mirror. The image below shows the set-up used here. For a waist-size of 8 mm and beam wavelength of 1550 nm, […]