REVIEW: Coherent Obis Galaxy laser combiner
(originally published here: http://blog.everydayscientist.com/?p=3174)
We recently purchased new lasers for our TIRF scope. I wanted the flexibility and low cost of a home-built laser combiner, but also I wanted the ease and stability of a turn-key laser box. I stumbled upon Coherent’s Obis Galaxy combiner, which uses up to 8 fiber pigtailed lasers and combines the emission into one output fiber. What I really love about the idea is that you can add lasers in the future as your experimental needs grow. (Or your budget does.)
The other aspect I love is that it’s just plug and play! If I were on vacation when a new laser arrived, anyone in lab should be able to add it to this system.
We also purchased the LaserBox, which supplies power, cooling, and separate digital/analog control to 5 lasers.
The new system just sits on the shelf. It’s tiny:
Here it is in action. The lasers were being triggered and sequenced by the camera and an ESio board, so they were running so fast I had to jiggle my iPhone in order to see the different colors.
One problem that I have faced is that the throughput is lower than spec (should be 60%+, and it’s down at 40%). Coherent is going to repair or replace the unit. And fortunately, we’re only running the lasers at 10% or less for most experiments currently, so there’s no rush to get the throughput higher!
If you’re ever in Genentech Hall UCSF and want a quick demo, drop me a line!
- Flexibility to add laser lines or upgrade lasers in the future at no additional cost (besides the pigtailed laser itself) and no downtime
- Super easy installation
- Cheaper than many of the other turn-key boxes
- No aligning or maintenance needed
- Each laser can be separately triggered and modulated (digital and/or analog)
- Replaceable output fiber if it gets damaged (although it might not be as high-throughput as the original fiber)
- Small and light, so it’s easy to find a place for it in any lab
- No dual-fiber output option
- Two boxes and some fibers going between the two makes it a little less portable than some of the other small boxes
- No space to add optics (e.g. polarizers) in launch
- Fans for LaserBox are not silent
- Power and emission LEDs are too bright
- NA of Coherent fiber is slightly smaller than that of Nikon TIRF illuminator expects, but the effect is barely observable (Coherent is working on a second fiber option that would even better match the TIRF illuminator)
Bottom line: I’d definitely recommend the Galaxy if you’re primary goals are color flexibility and simplicity. If you want more turn-key (and probably stability, but I can’t speak to that yet), there are other boxes to consider: Spectral ILE, Vortran Versa-Lase, Toptica MLE, and so on. Also, if you needed two (or more) fiber output, the Galaxy doesn’t have that option.
Edit 11/10/2014: I’ve found one issue. The NA of the Coherent fiber is smaller (0.055) than the standard Oz Optics fiber that Nikon uses for the TIRF launch (0.11). That means that the illumination is more compact at the sample. Because the beam is Gaussian shaped, that means that the illumination is less flat (i.e. very bright in the center and darker on the edges). I’m going to try a solution using a second fiber with the correct 0.11 NA and an Oz Optics AA-300 lens style universal connector. I’ll update if this works…
Edit 3/5/15: So it turns out that the NA difference isn’t that huge. Most of the discrepancy is just a difference in the way the two manufacturers report the NA. Not only that, but in practice the NA difference makes a tiny change in the illumination area in TIRF. I wouldn’t let the different NA stop you from considering this product. Also, Coherent is working on second fiber option that would even better match the TIRF illuminator. Contact Coherent to see if they can make one with a 0.074 NA (1/e2) output to match the NA of the Oz Optics (Corning) fibers that the Nikon illuminator expects.
Edit 7/30/15: The LaserBox has a 50 Ohm impedance for the digital modulation (2 kOhm for analog), because it needs to be able to driven up to 150 MHz, according to Coherent. This makes controlling the digital TTL with an Arduino a challenge, because the Uno is rated for 40 mA max. The ESio board (and maybe the TriggerScope?) can handle the higher currents. That said, the Arduino Uno seems to handle the higher current draw even though it’s not spec’ed to: I have a lot of anecdotal evidence that you can use an Arduino to control Obis lasers. (Maybe not 2 lines simultaneously?) Contact Coherent before you order to see if they can send one with higher impedance for the TTLs.