Pump scenarios

A pump scenario is a named operating point of a model: it states, for every amplifying component, how strongly that component amplifies during one analysis. Scenarios belong to the document, not to any node, and are stored in the .opm file. For the reasoning behind that split see Amplification; for the steps to set one up, see Model an amplifier.

A scenario consists of a name and, per node, a gain model. A node no scenario mentions is analyzed exactly like the passive component it is.

Managing scenarios

Scenarios are created by typing a name in the “New scenario name” field at the top of the pump scenario panel and pressing Add (or Enter). An existing scenario can be duplicated — button with the copy icon (⧉) next to the delete button on the scenario card, or via right-click → Duplicate on the card — which creates a copy of the scenario, including all its node configurations, with “ (copy)“ appended to the name. Both the original and the copy can then be edited independently. Duplicating is undoable.

Gain models

None

No amplification. The default, and what every node not named by the scenario falls back to. A node set to None behaves like the passive optic it is.

Const

A constant energy gain. The energy of the light passing the medium is multiplied by the gain factor, once per traversal of the medium.

gain factor: The factor the energy is multiplied by. Must be finite and non-negative; 1.0 is neutral, so selecting Const does not change a result until the factor is set. The factor does not depend on wavelength, on the path length through the medium, or on how much energy was already extracted — see Amplification for what this model is and is not good for.

Small Signal Gain

A monochromatic, unsaturated gain model. A pump source fills the component’s volume with a spatial gain field; each ray accumulates gain along the actual path it takes through the medium. The gain coefficient g₀ is wavelength-independent — all wavelengths in the beam receive the same gain. For the underlying concepts see Amplification.

grid (n_x × n_y × n_z): Number of cells in the discretized gain field, along x, y (transversal) and z (longitudinal). The ray traverses each cell exactly (Amanatides–Woo algorithm), so finer grids resolve spatial structure in the pump profile more accurately without any additional step count. All three must be at least 1. Default: 16 × 16 × 16.

Pump source

The pump source defines the spatial distribution of the small-signal gain coefficient g₀ across the medium’s volume.

None

No pumping. The gain field is zero everywhere; the component behaves passively.

Const

A spatially uniform g₀.

peak gain coefficient (g₀): The small-signal gain coefficient, uniform across the volume. Must be finite. Negative values model an absorbing medium. Unit: m⁻¹ (or cm⁻¹).

Analytic

A spatially profiled g₀, composed of independent transversal and longitudinal factors. The coefficient at each point is g₀ × T(x, y) × L(z), where T and L are each peak-normalized to 1 at the profile center or inlet.

peak gain coefficient (g₀): The peak value of the profile, at the center of the transversal profile and the inlet of the longitudinal one. Same rules as for Const.

Transversal profile — across the aperture (x–y plane):

Flat

Uniform across the aperture; T(x, y) = 1 everywhere.

Super-Gaussian

A generalized Gaussian, peak-normalized to 1 at the center.

center (x, y): Center of the profile in the component’s local frame. Unit: length. Default: (0, 0).
sigma (x, y): 1/e² half-widths along x and y. Must be positive.
power: Gaussian order (≥ 1). 1 gives an ordinary Gaussian; higher values give a flatter top with steeper edges (top-hat limit).
theta: Rotation of the ellipse in the transversal plane.
rectangular: If enabled, the profile is the product T_x(x) × T_y(y) instead of an elliptical function of the radial distance — useful for rectangular pump beams.

Longitudinal profile — along the propagation direction (z):

Flat

Uniform along z; L(z) = 1 everywhere.

Lambert-Beer

Exponential absorption of the pump: L(z) = exp(−α × z), where z is measured from the surface the pump enters.

absorption coefficient (α): Absorption coefficient of the pump light in the medium. Must be positive and finite. Unit: m⁻¹ (or cm⁻¹).
direction: Forward — pump enters from the input surface (z = 0 there). Backward — pump enters from the output surface (z = 0 at the rear face).

Which components can amplify

Only nodes that enclose a volume of material can carry a gain model:

This follows from the node type itself, not from a list maintained in the user interface, so a node type gaining a volume in the future becomes usable as an amplifier without anything else being changed. Other node types do not offer the setting.

Amplifier candidate. Marking a node as an amplifier is bookkeeping for the user interface: it determines which nodes the scenario editor offers a row for and what the canvas shows on the node. It is not what makes a component amplify. The analysis reads the gain model in the scenario and nothing else — worth knowing when a model is built in code, where the marking is optional.

Running an analysis in a scenario

Each analyzer carries a list of the scenarios it is run in, alongside its own configuration (see Analyzers). The list behaves as follows:

One report per scenario, produced in the order the scenarios are listed. The report’s analysis type is extended by the scenario’s name, e.g. Energy Analysis - full power, so the reports of one model at different operating points are told apart by their title.
An empty list means a single passive run — the behaviour of every analyzer before scenarios existed. This is not an error and needs no scenario to be defined.
Every run starts from the same model state, so scenarios do not influence one another regardless of the order they are listed in.
Deleting a scenario removes it from the selection of every analyzer that referred to it. An analyzer pointing at a scenario that does not exist is reported as an error before the analysis starts, rather than silently running passively.

Effect on the individual analyses

Const is evaluated in all three analyses:

Energy Analysis: The spectrum passing the component is scaled by the gain factor.
Ray Tracing Analysis: Every ray of the bundle inside the medium is scaled by the gain factor, between the entrance and the exit surface of the component.
Ghost Focus Analysis: As in ray tracing, and applied on every pass — including the reflected paths. A ghost that crosses a pumped medium twice more than the main beam is amplified twice more.

Small Signal Gain is evaluated in ray tracing and ghost focus analysis only:

Energy Analysis: Not supported. The gain depends on the path each ray takes through the medium; an energy flow analysis carries no spatial or geometric information about individual rays and cannot determine it. A model that assigns Small Signal Gain to a component returns an error when an Energy Analysis is run on it.
Ray Tracing Analysis: The gain factor for each ray is computed by integrating g₀ along the ray’s actual path through the medium. Rays that do not intersect the medium’s volume are unaffected.
Ghost Focus Analysis: As in ray tracing, computed independently on every pass — including reflected ghost paths. A ghost that traverses a pumped component picks up gain on each crossing.