532nm and 520nm are both common green lasers in the laboratory. The difference is that one is a diode pumped solid state(DPSS) laser and the other is a semiconductor laser.
532nm is a commonly used wavelength in dpss laser. DPSS lasers have advantages in compactness and efficiency over other types, and high power DPSS have replaced ion lasers and flashlamp-pumped lasers in many scientific applications, and are now appearing commonly in green and other color laser pointers.
The choice of the semiconductor material determines the wavelength of the emitted beam, which in today’s laser diodes range from infra-red to the UV spectrum. Laser diodes are the most common type of lasers produced, with a wide range of uses that include fiber optic communications, barcode readers, laser pointers, CD/DVD/Blu-ray disc reading/recording, laser printing, laser scanning and light beam illumination. With the use of a phosphor like that found on white LEDs, Laser diodes can be used for general illumination.