Finesse 2 support

Supported legacy syntax

Finesse 3 supports most common Finesse 2 syntax via its legacy parsing mode. Legacy parsing is available either via the Command line interface (using --legacy) or in Python using Model.parse_legacy() or Model.parse_legacy_file().

The Finesse 2 syntax supported by the legacy parser is listed below, along with links to the relevent Finesse 3 KatScript syntax and Python API. Directives not listed below are not supported. The supported parameters for each directive can be found in the Finesse 2 manual.

Warning

Support for Finesse 2 script support is only provided as a convenience to assist in transitioning to Finesse 3. New scripts should always be written in Finesse 3 script.

Components

Legacy name(s)	New name(s)	Python API
`bs` `bs1` `bs2` `beamsplitter`	`bs`	`Beamsplitter`
`cav` `cavity`	`cav` `cavity`	`Cavity`
`dbs`	`dbs`	`DirectionalBeamsplitter`
`gauss` `gauss` `gauss*`	`gauss`	`Gauss`
`gouy`	`gouy`	`Gouy`
`isol` `diode`	`isol` `isolator`	`Isolator`
`l` `laser` `light`	`l` `laser`	`Laser`
`lens` `lens` `lens` `lens**`	`lens`	`Lens`
`m` `m1` `m2` `mirror`	`m` `mirror`	`Mirror`
`mod`	`mod` `modulator`	`Modulator`
`sq` `squeezer`	`sq` `squeezer`	`Squeezer`
`s` `space`	`s` `space`	`Space`

Detectors

Legacy name(s)	New name(s)	Python API
`ad`	`ad`	`AmplitudeDetector`
`beam`	`ccd` `ccdline` `ccdpx`	`CCD` `CCDScanLine` `CCDPixel`
`bp`	`bp`	`BeamPropertyDetector`
`xd`	`xd`	`MotionDetector`
`pd[n]`	`pd` `pd1` `pd2`	`PowerDetector` `PowerDetectorDemod1` `PowerDetectorDemod2`
`qnoised[S/N]`	`qnoised` `qnoised1` `qnoised2`	`QuantumNoiseDetector` `QuantumNoiseDetectorDemod1` `QuantumNoiseDetectorDemod2`
`qshot[S/N]`	`qshot` `qshot1` `qshot2`	`QuantumShotNoiseDetector` `QuantumShotNoiseDetectorDemod1` `QuantumShotNoiseDetectorDemod2`

Commands

Legacy name(s)	New name(s)	Python API
`attr`	Replaced with arguments to the relevent components.	See relevent component constructors.
`attr mass` `attr tf`	Replaced with dedicated mechanics components e.g. `pendulum`, `free_mass`.	See components under `components.mechanical`.
`fadd` (Implemented in Finesse 3 as `freq name frequency`)	Not implemented.	`Model.add_frequency`
`fsig name f` (Setting the frequency)	`fsig`	`Model.fsig`
`fsig name comp ...` (Applying a signal)	`sgen` `signal_generator`	`SignalGenerator`
`func` `set` `put` `put*`	Replaced with KatScript Expressions and references.	`Symbol` `Parameter.ref`
`lambda` `lambda0`	`lambda`	`Model.lambda0`
`lock` `lock*`	`lock`	`Lock`
`mask`	Replaced by `mask` property of the relevant detector.	`MaskedDetector.mask`
`maxtem`	`modes`	`Model.modes`
`pdtype`	Use pdtype keyword argument for detectors	Use pdtype keyword argument for detectors
`phase`	Not implemented.	`Model.phase_level` `Model.phase_config`
`retrace`	Not implemented.	`Model.sim_trace_config`
`startnode`	Replaced by priority argument to `gauss` / `cav`.	`TraceDependency.priority`
`tem`	`tem`	`Laser.tem`
`var` `variable` `const`	`var` `variable`	`Variable`

Axes

Legacy name(s)	New name(s)	Python API
`noxaxis`	`noxaxis` N.B. This is now the default when no analyses are specified.	`Noxaxis`
`xaxis` `x2axis` `x3axis`	`xaxis` `x2axis` `x3axis`	`Xaxis` `X2axis` `X3axis`
`yaxis`	Not implemented.	`Model.yaxis`
`scale`	Not implemented.	Not implemented.

Internal differences from Finesse 2

Modulator sideband amplitudes

Finesse 2 uses a Bessel function routine optimised for speed of calculation. This causes modulator field amplitudes to be incorrect by a small amount only for extreme values of modulation depth when more than one modulation is performed. Finesse 3 uses a correct implementation, and so will differ from Finesse 2 slightly.

The following table lists the modulation indices for which Finesse 2’s error is distinguishable from numerical noise (greater than \(10^{-14}\)):

Order, \(n\)	Modulation index, \(m\)
1	Always Correct
2	\(0.482 \le m \le 2.0\)
3	\(0.958 \le m \le 3.0\)
4	\(2.128 \le m \le 4.0\)
5	\(2.920 \le m \le 5.0\)