The very earliest lasers worked in the microwave, infrared, and red regions of the electromagnetic spectrum. Helium-neon-based green lasers soon followed. The invention of the laser diode in the early 1960s led to today's small, hand-held green laser pointers.

Source

Helium-neon (HeNe) lasers can be designed to produce green as well as red light. Laser diodes are also used. Since don't normally emit green light, laser makers use a longer-wavelength diode, then pass the light through a device that changes it to green.

Wavelength

Green laser light comes in several wavelengths. HeNe lasers are typically 532 nanometers (nm). Diode types emit 523, 532, 542 nm and similar wavelengths.

Power

The power range of green lasers ranges from below 5 milliwatts (mW) to 500 mW. Compared to other lasers, these are low to moderate power levels.

Format

In 2009, diode-based hand-held pointers are the most common type of green laser. Larger, helium-neon devices see use in science and optics, where its wavelength is useful.

Visibility

Human eyesight is more sensitive to certain colors than others, and it's very sensitive to green in particular. Green lasers are more easily seen than other colors for a given power level.