A diode is a semiconductor device that allows electrical current to flow in one direction while blocking it in the other.
The basis of a solid-state diode laser is, of course, the diode. Laser diodes can have different emission wavelength—most of them have between 405 nm to 808 nm. The diodes usually have TO3, TO5, TO9, ...
A diode is a device that allows electric current to flow in only one direction, from its anode towards its cathode but not the other way around. There is plenty of online material explaining diode ...