Getting started

This page takes you through a first bench: a laser, a lens and a screen. It then tours the window, and shows how to keep and share what you make.

A first bench

1. Open JEKray. A new bench is empty. If it isn’t, choose File › New bench.
2. Click + Add part (or press A), choose Source, and click the bench to place it. A fan of rays leaves it to the right.
3. Add a Lens about 50 mm to the right of the source, and a Screen beyond it, facing back towards the light.
4. Drag the screen along the beam. Its panel on the right shows the spot it records. The spot is smallest at the lens’s focus.

The window

The bench is the large dark area. Drag an element to move it, drag its round handle to turn it, and scroll to zoom. Drag on empty bench to select several elements with a box. Right-click for a menu of what you can do with what is under the pointer.

The parts rail runs down the left edge of the bench. Its coloured buttons choose a palette of parts:

• Free space (orange): free-space optics;
• Fibre (red): fibre components;
• Electronics (amber): electronics;
• RF (yellow): millimetre-wave horns, lenses and mesh filters;
• Draw (purple): drawing tools for figures.

The buttons below the palette open groups of parts.

The panel on the right shows whatever is selected. With nothing selected, it shows the whole bench: its parts, notes and settings. With an element selected, it shows that element’s settings and readouts.

The bar along the top holds the File menu (under the bench’s name), + Add part, Undo and Redo, and the View, Sweeps and Help menus. Save shows a dot when the bench has changed since it was opened or saved. On a phone the bar is one row: the name, +, Save and ⋯, a menu holding the rest.

The 3D view

For a first go, take the tour under Help › Build a periscope in 3D: it builds a periscope step by step, tipping two mirrors with their rings.

The 2D / 3D switch at the bench’s top right (or View › 3D view) shows the tab in three dimensions. Every part sits at the beam height, 75 mm above a breadboard, and is made from its own numbers: a lens from its surfaces, a mirror from its curvature. The light is drawn as the trace has it: rays as lines, and Gaussian beams as tubes as wide as the beam is, in the bench plane and out of it.

Choose between them with the Mouse menu on the 3D view’s bar. On a touch screen, one finger turns, two pan and pinch to zoom. F fits the view to the parts, Z zooms to the selection, and Shift+1 to Shift+7 give the front, back, left, right, top, bottom and isometric views. Click a face, edge or corner of the view cube to look from there. PNG saves the view as a picture. The eye beside each part in the Bench panel’s list hides it in the 3D view, to see past a housing or a mount; the light still meets it as before.

Arranging parts in 3D. Drag a part to slide it across the table: it snaps to the grid as on the 2D bench, and a selection of several moves together. Right-click a part, or the bench, for the same menu as in 2D: duplicate, copy and paste, rotate, lock, move to another tab and the rest. A part added from + Add part lands where the view is looking, and one dragged from the parts rail lands where it is dropped. Undo and redo work as ever.

Objects from CAD. Mounts, posts, housings and baffles come in as .stl files: Open ▾ → Import an object (.stl), or drop the file on the bench. Each is an opaque STL object, placed and turned as any part, that stops the light that meets it.

Moving a part along x, y and up. Click a part and three double-ended arrows appear, out of both sides of it: orange along the bench’s x, green along its y, blue straight up. Drag either end of an arrow to move the part along it alone, snapped to the grid (up in 0.5 mm steps, Shift: 0.1 mm), or type it in X, Y and z in its panel, where each can be swept like any other number. The light follows a part’s height: a part above or below the beam is missed, and a lens or curved mirror met off its centre turns the beam up or down (see Free-space optics: heights). On the 2D bench, a part not at the beam height shows by how much under its name.

Turning a part about its three axes. Click the part again and the arrows give way to three rings of one size round it, square to each other and crossing, each the colour of the axis it turns about:

• the blue ring, flat round the part, turns it to face another way (its Facing);
• the green ring, upright through the way it faces, tips it up or down about its own across axis, as the vertical knob of a kinematic mount does (its Tip);
• the orange ring, square to the way it faces, rolls it about its own axis, right-handed (its Roll): a cylindrical lens at 45°, a Dove prism turning the image, a waveplate’s axis.

Drag a ring round, by its dot or anywhere on it (the dot sits an eighth of a turn from where the part is turned to, clear of where the rings cross, and moves round with it): Shift turns in 15° steps, and Alt a tenth as fast, for fine alignment. Click the part a third time for its arrows again. Two mirrors tipped against each other walk a beam up and leave it level, as on a real bench; two tipped 45°, one over the other, make a periscope. A tipped source sends its light up at that angle. A tipped or rolled part shows by how much under its name on the 2D bench.

The 3D view is a view of the same bench: select a part and its panel opens as usual, and anything you change there shows at once. Any tab opens in 3D: its free-space parts are drawn there, while fibre, electronic and chip parts show in 2D only (their light leaves and reaches the free-space parts as ever). Drawings show in 2D only.

Settings and sweeps

Every number in a panel can be typed or dragged. Beside most is the sweep button, ∿: it moves the value back and forth over a range, and the bench follows as it plays. A swept number shows its sweep folded to one line, with Play; click the line, or ∿, to edit it. A panel’s sections fold away under their headings, and the longer explanations are kept under About this part at the foot. That is the quickest way to see how a system depends on one thing. The Sweeps menu also holds an optimiser and a tolerance study. The pin at the top of a panel keeps it open while you select other things, and its × closes it: a pinned panel is unpinned, and the main panel goes until you select something again (or choose View › Show the side panel).

How the light is drawn is set for the whole bench, under Light in the Bench panel (the gear at the bench’s bottom right opens and closes it; a click on empty bench closes any panel): three ticks for the rays, the Gaussian beams’ envelope and their diffracted field, each on or off. The field’s Field intensity is linear, or logarithmic over 30 dB or 60 dB. With both on, the envelope marks the field’s 1/e² edge.

In the 3D view the diffracted field glows along each beam as light scattered out of it by a faint haze would: each point on the picture shows the irradiance added up along that line of sight, in W/mm against the key at the bottom left. Seen side-on through a beam’s middle that is its power per mm across it; where beams cross, or you look along one, their light adds. Point at the light to read the light along that line of sight, and the brightest irradiance on it and where it is. Beams of one laser running together add as fields, so an interferometer’s dark port is dark here too; beams crossing at an angle or running opposite ways add as intensities, their fringes being far finer than the view. A tight focus is far brighter than the beam that makes it, so choose 60 dB to see both; on a slow computer or a phone, untick the field to leave the beams as outlines.

Saving and sharing

• Autosave. Your bench is kept in this browser as you work, so closing the tab loses nothing.
• File › Save as .jekray saves a file you can open again anywhere.
• Share link puts the whole bench in a link. Anyone who opens it sees your bench, and nothing is stored on a server.
• File › Export layout saves a PNG, SVG or PDF of the bench for a paper or a talk. Export layout (current view) saves just what is on screen.
• With JEKrayPro, benches can be saved to your account, with version history, forks and team workspaces.

Where to go next

• Concepts: coordinates, units and the ideas the rest of these pages use.
• Free-space optics: how rays, beams and fields are worked out.
• The FAQ, for common questions.