Peace All
Spectra and lasers actually fall under Optics but knowledge of geometry is required to understand the fundamentals of how prisms work.
Prism has two definitions … one is that which splits light and the other is a 3D object.
In geometry prism is a defined word for extruded 2D shapes that appear as rectangular in the height dimension. For example a tube is a circular prism, where the cross-section is a circle and the length is a rectangle. A cuboid is a prism too. The shape of a Toblerone chocolate bar is a triangular prism and so on.
In terms of optics, firstly light is a mixture of photons moving in an array of ways they have a sense of frequency and wavelength and certain energies correspond to these. Light is part of the electromagnetic spectrum most of which is invisible to us. It is interesting that green is the middle colour of the visible spectrum and hadith mentioning that it is favoured by our prophet Muhammad (SAW), such that he always chose the middle path as the one to tread, favourite colours it seems were no exception.
Green light has special characteristcs in that it is the brightest perceived colour in dark/twilight conditions, which makes it a useful colour in the dark … it can be seen as the colour of guidance. Another interesting fact.
White light contains a mixture of all the visible colours and light from the sun contains many things besides just visible light. Gamma rays are stopped at the atmosphere (mostly). All things give off photons in the Infra Red region. It should be considered a blessing that we cannot see infra-red, or else we would constantly be in light without dark to go to sleep in.
The basis of prisms works on refraction. This is a method of splitting colours from a mix of light. Different colours have different energy levels, which means they have different physical characteristics.
File:Light dispersion conceptual waves.gif - Wikipedia
The properties of prisms are that they allow light to enter, but they bend light on the interfaces. The amount they bend light differs on the wavelength and hence you have something called dispersion, and the light spreads out, in to an array of colours.
Lasers are made using prisms of a special type. They are fine crystals that end up blocking other types of light allow few ranges through and increase intensity by constructive interference. A laser contains coherent light which means it is of one colour and all of it is polarised in the same way. Polarity is the physical plane of the laser light. A laser light should have no spectrum it should not disperse a lot in a prism if it is any good.
The way polarised sunglasses work is by allowing the diffused light in, but stopping transverse waves which are polarized to the horizontal plane. They become transverse by a series of reflections of flat surfaces causing something known as glare. If two polarised lenses are placed over one another you will get an interesting effect of total black out when you cross their polarised planes.
Another type of polariser is the circular form, which does many more interesting things.