OSRAM unveils direct-emission green laser diodes emitting at wavelengths from 510 to 530 nm

The 30 and 50 mW laser diodes have the correct visual green color for projectors and light shows.

May 13th, 2019
OSRAM unveils direct-emission green laser diodes emitting at wavelengths from 510 to 530 nm
OSRAM unveils direct-emission green laser diodes emitting at wavelengths from 510 to 530 nm
An output spectrum (left) as a function of temperature is shown for an example OSRAM true-green laser diode (right). (Images: OSRAM)

Indium gallium nitride (InGaN)-based laser diodes are straightforward to fabricate in blue-emitting versions, but are more difficult to make so that they emit in green -- especially the longer-wavelength green that humans perceive as true green: early green laser diodes have typically had a slight cyan cast. OSRAM Opto Semiconductors (Regensburg, Germany), which was a commercial pioneer in the introduction of green-emitting InGaN laser diodes, has been pushing the long-wavelength boundary and has now introduced InGaN-based direct emission green laser diodes with wavelengths from 510 to 530 nm for picoprojection and other red-green-blue (RGB) or green laser applications. (OSRAM also make blue laser diodes.)

The 510 to 530 nm range encompasses "true green."

Mounted in a TO38icut or TO56 package (these are quite small, with flange diameter of 3.8 mm) with integrated photodiode, these lasers have a typical divergence angle of 7° parallel and 22° perpendicular, small enough for circularization and collimation with relatively simple optics. This is an important property for micro-electro-mechanical systems (MEMS)-based projectors in which the color components per pixel result ›from the emission time of the laser diode, says OSRAM.

Existing small green-laser competition comes mainly in the form of frequency-doubled diode-pumped solid-state (DPSS) lasers of the form commonly found in the first green laser pointers. These lasers are relatively complicated, containing an infrared pump laser diode to pump the solid-state laser, and a nonlinear optical crystal to frequency double the resulting IR light into the green. In comparison, a direct-emission laser diode contains only -- well, a direct-emission laser diode.

Two of OSRAM's green laser-diode models, PL 520B & PL 520, have slightly different wavelength ranges at power levels of 30 mW or 50 mW at 25°C. The single-mode PL 520 laser diode has an output wavelength of 515 to 530 nm, an optical output is 50 mW and an efficiency typically of 5% to 6% at present, says OSRAM. The lasers have an operating temperature range of up to 85° C without active cooling.

Direct-emission green laser diodes can help enable practical high-power embedded projectors and could lead to the end of frequency-doubled DPSS lasers in small projectors. The lasers are also useful for laser light shows, as their high beam quality enables extremely fine structures to be displayed at a considerable distance, says OSRAM. The projectors also benefit from the high thermal stability and small size of the laser diodes. When used in point- or line-projecting lasers used, for example, in distance meters by builders, farther distances are possible because green light is far more visible than red at the same optical power.

Source: OSRAM Opto Semiconductors

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