# Are the bandwidths of a laser pointer and a sodium-vapor lamp comparable?

The question is not about the slightly differing wavelength of the devices caused by manufacturing processes or the shift from changing temperature.

A German source says that the spectral width with which laser diodes emit their light is only 1 nm, in the case of the Distributed Feedback Laser (DFB) it is only 0.1 nm. (“Die spektrale Breite mit der Laserdioden ihr Licht aussenden, beträgt nur 1 nm, im Falle des Distributed Feedback Lasers (DFB) ist sie sogar nur 0,1 nm.“) Could I suppose that a cheap laser pointer has a bandwidth of more than 1 nm?

The bandwidth of a sodium-vapor lamp has two spectral lines very close together at 589.0 and 589.6 nm. This turns out that the bandwidth of this lamp is around 0.6 nm?

For the background see this question about The function of the pinhole in the double slit experiment and therein the comments below the answer.

At any rate all of these things will be sufficient to perform double-slit experiments. In a double slit experiment light from two slits $$d$$ apart (the slits are assumed to be much smaller than $$d$$ and larger than $$\lambda$$) interfere to after a distance $$L$$ to make maxima space by $$\delta=L\lambda/d$$. If you have multiple wavelengths then these will all diffract but with slightly different phase shifts (and thus spacing). But the relative shift in $$\lambda$$ is so small you should have no worries about fringes `running into each other' as it were.