Diode Stacks | previous | next | feedback |
You can buy diode stacks from:
- DILAS offers vertical, horizontal and two-dimensional CW and QCW stacks that have tight tolerances and can be customized to meet the performance and production configurations for stacked array solutions.
- JENOPTIK Laserdiode GmbH, manufacturer of high power diode laser stacks with or without collimation and up to 25 stacked elements, each with up to 120 W output power.
Ask RP Photonics for advice on how to select the right diode stack for your application.
Definition: arrangements of multiple diode bars, delivering very high output power
A diode stack (also called diode laser stack, multi-bar module, or two-dimensional laser array) contains a number of diode bars, which are arranged in the form of a stack. The most common arrangement is that of a vertical stack as shown in Figure 1. Effectively this is a two-dimensional array of edge emitters. Such a stack can be fabricated by cleaving linear diode laser arrays (diode bars) from a wafer, attaching them to thin heat sinks, and stacking these assemblies so as to obtain a periodic array of diode bars and heat sinks. There are also horizontal diode stacks (see below), and two-dimensional stacks.
Figure 1: Schematic structure of a laser diode stack. The emitters are shown in blue, and the microchannel coolers in dark gray.
For the highest beam quality, the diode bars should be as close to each other as possible. On the other hand, efficient cooling requires some minimum thickness of the heat sinks which need to be mounted between the bars. Due to that minimum spacing, the beam quality of the combined output of a diode stack in the vertical direction (and subsequently its brightness) is much lower than that of a single diode bar. There are, however, several techniques for significantly mitigating this problem, e.g. by spatial interleaving of the outputs of different diode stacks, by polarization coupling, or by wavelength multiplexing. Various types of high-power beam shapers and related devices have been developed for such purposes.
Depending on the application, a diode stack may be used with or without attached optics. A common option is the use of fast axis collimation lenses, which are directly attached to the bars (see Figure 2). Further optics can be used for collimation also in the slow axis (horizontal) direction, or even for coupling the output into a multimode fiber.
Figure 2: Photograph of water-cooled diode stacks, kindly provided by DILAS. The number of diode bars varies from 1 (left-hand side) to 10 (right-hand side). One device has fast axis collimation lenses attached to the bars.
Diode stacks can provide extremely high output powers of hundreds or thousands of watts, as used for pumping of high-power solid-state lasers, or used directly e.g. for material processing. There are also fiber-coupled diode stacks, delivering e.g. several kilowatts from a multimode fiber with a core diameter of 600 μm. Some applications such as welding of metals or plastics, where a high beam quality is not required, can directly utilize the output of such a laser system, which can have a very high wall-plug efficiency. This is also attractive for other direct laser diode applications such as hardening, alloying, and cladding of metallic surfaces. If laser radiation with much higher brightness is required, the laser radiation may be used for pumping a high-power fiber laser based on a double-clad fiber. Such a device can serve as a brightness converter, delivering a somewhat reduced output power but with much higher beam quality.
There are also horizontal stacks, where the diode bars are arranged side-by-side, leading to a long linear array of emitters. Such an arrangement is more easily cooled, and may thus also allow for a higher output power per emitter. The emission pattern of a horizontal stack is suitable for, e.g., pumping of rod lasers, whereas it is probably less convenient when an approximately circular output beam is required. The number of diode bars in a horizontal stack (and thus the total output power) is more limited than in a vertical stack.
The cooling of such diode stacks is somewhat challenging for continuous-wave operation, but less so for quasi-continuous-wave operation with pulses of e.g. a few hundred microseconds duration and a pulse repetition rate of some tens of hertz. The latter mode of operation makes it possible to obtain very high peak powers, which can be used e.g. for pumping Q-switched high-power solid-state lasers.
See also: laser diodes, diode bars, fiber-coupled diode lasers, high-power lasers, brightness, wall-plug efficiency
Since October 2008, the Encyclopedia of Laser Physics and Technology is also available in the form of a two-volume book. Maybe you would enjoy reading it also in that form! The print version has a carefully designed layout and can be considered a must-have for any institute library, laser research group, or laser company.
You may order the print version via Wiley-VCH.
