Getting started with JamMt

When you start JamMt for the first time you will only see the profile of a Gaussian beam with a default radius of 370 μm and the waist located at the origin.

Adding a thin lens

Let's add a lens to the plot using 'Edit->Add substrate' (by the way: the word 'substrate' means a certain material with refractive index, thickness, two interface (that may be curved), etc.; it can be used to simulate thick (i.e. real) lenses). Per default you can add a thin lens with a focal length of 0.1 m, so just press 'Ok' to start playing with JamMt. After you've done that the lens will be shown in the plot. Now you can drag it with the mouse and see the behaviour of the beam online.

Get some information

The status bar at the bottom of the JamMt window shows you the actual waist size as well as its position of the resulting beam (i.e. the beam after the rightmost substrate). You can get additional info in form of a tooltip if you point the mouse over a lens or the beam. You can also use 'View->Verbose' to constantly show a box containing information about a substrate. In that case the initial beam parameters will be shown in the statusbar, too.

Beam analyzer

To get information about the beam at a specific location use 'Edit->Add beam analyzer' and choose a name and a position in the window that just popped up. You can interact with an analyzer the same way as you would do with a lens. An overview of all analyzer can be displayed using 'Window->Beam analyzer' from the menu bar. From this window you can get even more information about the beam.

Thick lenses

Now it's time to add another lens, so choose 'Edit->Add substrate' again and add a thick lens by clicking the button 'Advanced'. Now you have access to all text fields. If you choose for example 'n=1.5' and a radius of curvature of -/+ 200mm (left/right), you will get a lens with a focal length of approximately 200 mm.

Groups

Now try to collimate your beam and after that press a number key (1-9). This will add the currently active lens to the group with the given number. Press 'TAB' to activate the other lens and press the same number key again. Now the two lenses are grouped and you can move them together. To ungroup a single lens press the key 'u' or press 'Shift-u' to ungroup all lenses in the current group.

Simulate cavities

The next step is to create a linear cavity. To achieve that we will change the two lenses slightly to represent cavity endmirrors (NOTE: a cavity mirror has to be a thick lens). Double click one of your substrates and change the 'inner' radius of curvature to 300 mm, say. Do the same with the other substrate. You can see from the plot if you got the signs right to form a symmetric cavity. Now mark the left mirror by pressing 'Shift-8' and the right one by pressing 'Shift-9'. Now you will be provided with a dialog on which you can further specify the cavity. For now giving just a name will be sufficient. After pressing 'Ok', a window containing some information about your cavity (including the modematching 'V' and the stability parameter 'g') will be shown. You can now change the cavity length and see how the eigenmode changes.

Mode matching made simple

Now we'll have a look at the fitting routine that automatically solves your modematching problems. First delete your substrates using the 'Del' key and go to 'Tools->Modematching assistant'. In this window you can specify the initial beam parameters, the parameters of the target beam, the range in between the lenses should be moved, as well as the desired visibility (overlap between initial and target waist) and the number of lenses that should be used for the modematching (this is currently limited to three lenses at most). The lenses that are used for the fit can be edited by pressing 'Edit lenses'. The default is to use thin lenses with a focal length of +/- 100 mm. When you've edited everything to your needs, press 'Start search' to start the search for possible modematchings.
When the search has finished, you can choose a solution from the list and it will be shown in the plot. If you got the message that all solutions were filtered out, then you may try to change the filter settings (click 'Result filter'), or to be less restrictive on the settings for the modematching.

Learn more

This should be enough to get started with JamMt. For further information please browse the documentation. Here are a few things that you might be interested in: