If you’ve ever dug into how 808nm vertical stack diode lasers work, you’ve probably run into one question that pops up way more than you’d expect: “What’s their divergence angle?” And as someone who’s spent the last 7 years selling these things (I’m not gonna name-drop, just know we’ve shipped thousands of stacks to folks making everything from medical hair removal rigs to industrial material processing gear), this is the question we get at least once a day. A lot of people come in assuming divergence is a one-number, set-in-stone value—like a laser’s wavelength. But nope, with vertical stack diodes, it’s way messier, and way more dependent on what you’re actually using the stack for. Let’s break this down like we’re chatting over a coffee, no stuffy textbook jargon that’ll make your eyes glaze over. 808nm Vertical Stack Diode Laser
First, let’s get on the same page about what an 808nm vertical stack diode even is. If you’re new, don’t overcomplicate it. A single diode laser chip is like a tiny, skinny light-emitting rectangle, right? It emits light in one super narrow axis (that’s called the fast axis) and one a little wider (slow axis). A vertical stack is just stacking dozens of these tiny chips on top of each other, like layers in a cake, to cram way more power into a smaller space. We’re talking 10W per chip, 20 to 100 chips in a stack, so you can get a 200W to 1000W+ laser out of one unit. That’s why they’re so popular—you don’t need a bunch of separate small lasers when you can stack ’em all in one.
Now, divergence angle. The super basic definition: how much the laser beam spreads out as it travels away from the emitter. The smaller the angle, the tighter the beam, and the farther it can go without getting all blobby. For single diodes, you’ll hear numbers like 9 degrees for the fast axis and 25 degrees for the slow axis, right? But when you stack them, that’s where things change. Wait, no—actually, the individual chips’ divergence is still close to that, but when you stack them, the whole stack’s beam doesn’t just add those angles up. There’s a catch here: most people measure divergence differently, and what’s “standard” depends on who you ask.
Let’s split this into the two axes, because that’s where all the action is, with vertical stacks. Fast axis first: that’s the axis where the single diode is super skinny, like the width of a human hair basically. The divergence here is way smaller—usually between 6 and 10 degrees for a single chip, and for a stack, it barely changes. Wait, why? Because when you stack chips vertically, the fast axis is still perpendicular to the stack layers, right? So all the individual chips’ fast axis beams are aligned that way, so their divergence doesn’t add up. So on the fast axis, a typical 808nm vertical stack has a divergence of around 8 to 12 degrees, give or take a degree or two. That’s pretty consistent across most standard stacks. The slow axis is the wild card here. That’s the axis that runs parallel to the stack layers, along the length of each diode chip. For a single chip, that divergence is like 20 to 30 degrees, but when you stack multiple chips next to each other (wait, no—wait, horizontal vs vertical stack? Wait, hold on, I think I mixed up terms earlier, let’s correct that quick. For vertical stacks, the chips are stacked vertically, so the slow axis is horizontal across the chip array. So when you stack more chips side-by-side horizontally (wait, no, some stacks are 1cm wide, with chips arranged in a line horizontally, stacked vertically in height). So the slow axis is along that horizontal line of chips. So as you add more chips to the slow axis, the divergence angle there gets a little wider. Because each chip is emitting light, and their individual slow axis divergences add up a bit when they’re aligned side by side. So a small stack, like 10mm wide (20 chips) might have a slow axis divergence of 15 to 20 degrees, while a larger 20mm wide stack (40 chips) could be 20 to 25 degrees. That’s the main variable when it comes to divergence for vertical stacks.
But wait a second—why does this matter? Let’s use examples, because that’s what makes it real. If you’re making a laser for medical hair removal, you need a wide, uniform beam that covers a large area, right? You don’t want a super tight beam that only hits a tiny spot—you need to cover a patch of skin quickly and evenly. So for that application, you actually want a wider divergence on the slow axis, like 20 to 25 degrees. That works perfectly, because you can add some optics to shape the beam and make it flat over a large area. But if you’re using an 808nm stack for industrial pumping, like pumping a fiber laser or a solid-state laser, you need a tight, collimated beam that can be focused really small. For that, you want a smaller divergence, like 12 to 18 degrees on the slow axis, so you can couple the light into a fiber efficiently. If your divergence is too wide, you lose a ton of power when you try to focus it, which kills the efficiency of your whole system.
Here’s the thing that trips a lot of people up: suppliers often give divergence angles in full angle vs half angle. Full angle is the total spread, from one edge of the beam to the other, while half angle is the spread from the center to the edge. So if someone says 8 degrees full angle, that’s 4 degrees half angle. A lot of fly-by-night suppliers use half angle to make their numbers look better—they’ll list a divergence of 5 degrees, but that’s half angle, so full angle is 10 degrees, which is actually worse. That’s why it’s so important to ask for full angle, and what measurement standard they used. We always list full angle, because that’s what actually matters for your setup.
Another factor: packaging. Some vertical stacks are what we call “bare bars” vs “fast axis collimated (FAC)” stacks. A bare bar is just the stack of chips, no optics attached. Its divergence is wider, like 10-15 degrees fast axis, 20-30 slow axis. But almost no one uses bare bars these days, because you need to collimate the beam to do anything useful. When we sell our stacks, we usually add a fast axis collimation lens right at the top of the stack, which cuts the fast axis divergence down to like 8-10 degrees full angle. Some customers also add slow axis collimation lenses to narrow that angle even more, down to 10-15 degrees, for pumping applications. So the divergence isn’t fixed—you can tweak it with optics, depending on what you need.
Wait, let’s talk about power levels, because that also plays a small role. We have stacks that go from 100W up to 2000W, all 808nm. The higher power stacks, like 1000W+, usually have a slightly wider slow axis divergence, like 20-25 degrees, because we have to pack more chips into a larger area. But we balance that with optics to make sure the beam is still usable. For lower power, 100W to 500W stacks, we can get that slow axis down to 15-20 degrees easier, because the chip count is lower.
I’ve had so many customers come to us with wrong expectations about divergence. Last year, a startup making portable laser welders asked for an 808nm stack with a 5-degree divergence. That’s basically impossible for a vertical stack—5 degrees is almost the divergence of a single-mode fiber laser, not a diode stack. We explained that, and they ended up going with a 12-degree fast axis, 18-degree slow axis stack, which worked perfectly for their welding application. They tried to get a smaller angle from another supplier, who quoted them a number that was too good to be true, and they ended up wasting time and money on a product that couldn’t do what they needed.
Another common misconception: divergence only matters for the near field, like how the beam looks 10cm from the emitter. No, it also matters for the far field, like when you’re focusing the beam into a fiber or a workpiece. A wider divergence means more of the beam is outside the target area when you focus it, so you have higher power loss, and lower overall efficiency. That’s why pumping applications care so much about tight divergence—they can’t afford to lose 20% or more of their pump power just because the beam spreads too much.
So to sum up, the divergence angle of an 808nm vertical stack diode laser isn’t a single number. It depends on two axes, the power of the stack, whether it has collimation optics, and what measurement standard the supplier uses. For standard, collimated stacks, you’re looking at 8 to 12 degrees full angle on the fast axis, and 12 to 25 degrees full angle on the slow axis. If you need a specific number, tell us what your application is, and we can tailor the stack and optics to get you exactly the divergence you need.
At the end of the day, divergence is just one part of the puzzle. You also care about power efficiency, reliability, beam quality, and of course, price. We’ve been doing this for long enough that we know how to balance all of those. If you’re designing a new system, and you’re not sure what divergence angle you need, or you’re tired of dealing with suppliers who give you vague, misleading numbers, hit us up. We’ll walk through your application, give you real, tested divergence numbers, and build a stack that fits your needs, no fine print, no hidden jargon. We work with everyone from small startups to big industrial companies, so whether you’re making medical devices or cutting tools, we’ve got you covered.
Diode Laser Chips References:
- Chakrabarti, S. (2018). High-power diode laser bars and stacks: design, fabrication, and applications. CRC Press.
- Liu, J. M. (2005). Principles of diode lasers. Springer.
- Wang, Y., et al. (2020). Divergence characteristics of vertical stack diode lasers for pumping applications. Applied Optics, 59(12), 3645-3652.
Hangzhou Brandnew Technology Co., Ltd.
Hangzhou Brandnew Technology Co., Ltd. is one of the leading 808nm vertical stack diode laser manufacturers and suppliers in China, has a professional factory which manufacturers high quality 808nm vertical stack diode laser and sells at competitive price. Welcome to wholesale our products made in China.
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