The DPSSL - How It Works

The most common DPSSL in use is the 532 nm wavelength green laser pointer. A powerful (>200 mW) 808 nm wavelength infrared GaAlAs laser diode pumps a neodymium-doped yttrium aluminium garnet (Nd:YAG) or a neodymium-doped yttrium orthovanadate (Nd:YVO4) crystal which produces 1064 nm wavelength light. This light is then frequency doubled using a nonlinear optical process in a potassium titanyl phosphate (KTP) crystal, producing 532 nm light. Green DPSSLs are usually around 20% efficient, although some lasers can reach up to 35% efficiency. In other words, a green DPSSL using a 2.5 W pump diode would be expected to output around 500-900 mW of 532 nm light.

In optimal conditions, Nd:YVO4 has a conversion efficiency of 60%, while KTP has a conversion efficiency of 80%, in other words, a green DPSSL can theoretically have an overall efficiency of 48%.

In the realm of very high output powers, the KTP crystal becomes susceptible to optical damage. Thus, high-power DPSSLs generally have a larger beam diameter, as the 1064 nm laser is expanded before it reaches the KTP crystal, reducing the irradiance from the infrared light. In order to maintain a lower beam diameter, a crystal with a higher damage threshold, such as lithium triborate (LBO), is used instead.