FAQ

Common questions about what JEKray does, how far to trust it, and how to get the most from it.

General

Is JEKray free?

Yes. The simulator is free under the JEKray Licence. JEKrayPro is an optional subscription that adds a cloud account: benches saved online with version history, forks, team workspaces and your own parts library.

Does my bench leave my computer?

Not unless you choose to send it. The simulator runs in your browser and your bench is autosaved there. A share link carries the bench in the part of the address after #, which browsers never send to a server. Only benches you save to a JEKrayPro account are stored online.

Which browsers does it run in?

Current Chrome, Edge, Firefox and Safari. It runs heavy work in background threads, so a recent computer helps with large benches and the diffracted field.

Models

How accurate is it?

The ray tracer is exact for the geometry it models: real surfaces, real glass (Sellmeier data), Fresnel coefficients and coatings. The Gaussian-beam and diffracted-field models are paraxial except where they say otherwise. Near a steep focus the field is summed directly by the Rayleigh–Sommerfeld integral. The validation page compares the results with analytic answers and published data, and runs in your browser.

Why is everything in a plane?

A 2D bench is how most optical setups are drawn and planned, and it keeps the tool quick and clear. The diffracted field is still worked out properly. Each element is a figure of revolution about its axis in the plane, so a beam’s field out of the plane follows from its field in the plane. Where tilts break that symmetry, a full 2D field is used. What cannot be done is anything that leaves the plane, such as a periscope or skew rays.

Can I see my bench in 3D?

Yes: use the 2D / 3D switch at the bench’s top right (see Getting started: the 3D view). It shows the same bench in three dimensions. Every free-space part can be raised, tipped and rolled, and the light follows exactly, rays, beams and the diffracted field alike: periscopes, misaligned cavities, rolled cylinders and Dove prisms (see Free-space optics: heights). Each free-space part takes all six degrees of freedom (x, y, z, facing, tip and roll); fibre, electronic and chip parts are left out of the 3D view.

Why don’t two of my lasers interfere?

Light from separate lasers adds as powers, never as fields, as it does in the lab: two free-running lasers have no steady phase between them. On a photodiode they still beat at the difference of their frequencies, and that beat is listed with the line width of both. To make two beams interfere, make the second source split from the first. They are then one launch.

Why do my fringes fade?

Because the paths differ by more than the laser’s coherence length. A source with a line of its own has a coherence length \(L_c = c/\Delta\nu\), and fringe contrast falls with the path difference (see Concepts). Set the source to a single frequency if you want fringes at any path difference.

My cavity shows no resonance. What is wrong?

A cavity is found from the light’s own path, so the light has to make at least two round trips before the tracer stops following it. Raise Interactions per ray (on the Bench panel, under the gear at the bench’s bottom right) to about 40, and lower Power floor to about 1e-4 so faint round trips are kept. Then check that the mirrors face each other and the cavity is stable: the Bench panel’s Cavity tab says so.

What is the difference between rays and the beam?

A source can launch a ray fan, many rays across its width, and a Gaussian beam, one reference ray with a beam parameter. Ray fans show geometry: spots, aberrations, vignetting. The Gaussian beam carries the diffracted field: focus sizes, interference, coupling into fibres and cavity modes. You can have both at once.

Using it

How do I model a part from a catalogue?

Type in its prescription: radii, thicknesses, glass and diameter for a lens. Or import a Zemax file: File › Import a lens (.zmx) reads the files Thorlabs, Edmund and other makers publish. To take a lens the other way, File › Export a lens (.zmx) writes the lenses you have selected as a prescription that lens-design programs open; see Lens. With JEKrayPro you can keep parts in My parts to use on any bench.

Can an AI assistant build a bench for me?

Yes. Give it the guide for AI assistants, ask for a .jekray file, and paste its answer with Ctrl+V on the bench. Anything it got wrong is listed in an import report you can hand back to it.

How do I cite JEKray?

Help › Cite JEKray, or Cite on the bar, gives a reference to copy, with the version you used, and a BibTeX entry.

I found something wrong.

Please tell us at [email protected], or use Help › Report a bug. The same goes for anything wrong or unclear in these pages.