Hygroscopicity of LBO

[mophead]

How hygroscopic is LBO?

I snagged one of the B&W Tek 473nm that were on ebay a few days ago and plan to open the head to determine pinout, take some macro pics, ect. It is a rainy humid day here in the south - probably 80+% rH.

It will take longer than just a few minutes to do everything I want to do. Will it be okay to place the head, disassembled, in a sealed container with some dry CaCl2 or a few packs of silica gel in between times it is being worked on?

[mixedgas]

QUOTE:
It will take longer than just a few minutes to do everything I want to do. Will it be okay to place the head, disassembled, in a sealed container with some dry CaCl2 or a few packs of silica gel in between times it is being worked on?[/QUOTE]

No, you need to handle it in argon filled glove box.
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Just kidding!
SilIca Gel packs in a small bucket or lunchbox will be fine, the stuff doesn't melt into jelly on exposure to air, and the coatings on the faces protect the two optical surfaces. It can take weeks or months to degrade. One does want to keep any optics cleaning fluids on the coated faces.

Steve

[Kyle]

I opened mine up for the first time just yesterday, and took some shots today. It's quite humid here as well; I'll be ordering some silica gel packets this evening. I've attached a few pics of the cavity. I used a point and shoot so they're certainly not macro shots.

Although I've not personally seen the insides of a DPSS blue before I couldn't help but notice that the Nd:YAG crystal appears to be side pumped at an angle. Either that or it is some type of prism, I suppose. It is standing vertically underneath the aluminum cover with the red marking. When the laser is on I can see a thin line of blue light hitting the internal facet between the two sides of the crystal.

I've also been trying to temperature tune the laser but I'm not sure which pot controls the diode current and haven't wired the diode in series with a DMM to find out. I've adjusted two pots and both of them seemed to produce rather immediate results, with the lone pot closest to the laser head connector having a more dramatic affect than the center pot.

I got about 50% more output with the photodiode assembly attached by turning the center pot about two revolutions. I turned it back to the original setting as I'm unsure whether or not if this pot controls temperature or diode current.

I also noticed that when fiddling with the pot closest to the laser head connector with the photodiode assembly removed from the front of the laser the power output stabilized to about 30mW regardless of what the pot was set to. I'm beginning to wonder if the regulation circuitry overrides the potentiometer settings and increases diode current until a maximum current level is reached. I guess I'll have to go ahead and connect the multimeter in series with the diode to finally find out which pot, if any, controls the diode current.

- Kyle

[ElektroFreak]

the Nd:YAG crystal appears to be side pumped at an angle.

This arrangement is typically due to the use of an anamorphic prism pair for bump beam correction. There is probably a pair inside the black cylinder just after the pump diode, but it could also be some sort of other arrangement as well. It's hard to tell for sure without seeing inside the cylinder..

Also, to answer the OPs question, every blue DPSS laser I've seen personally has the LBO encased in a teflon container inside the laser head to protect it from moisture.

[MechEng3]

Sorry guys...its BiBo. The case is to proved a layer of protection from stray I/R and damage when assembled. The cavity is aligned in a fixture at the factory and set aside with the others in the line. They just drop in the cavity as a module component and align the pump spot....temp tune and off it goes. While no where that simple or fast, but it conveys the message. The anomorphics are coated and serve well for other purposes...The optics for beam compression/expansion are still in testing when I have time. Good for parts...the flaky ones...diode is a good transplant after a GRIN or FAC install.....2 watt unit....based on output levels from factory settings. Driver is good for up to 4 amps....

[mophead]

Cool, thanks guys.

I'm going to take some hi-res macro shots of everything in the cavity and the driver boards too. Not sure they will be up tonight, but they are comming. Also going to try and pinout the head and post it up as well.

Maybe I'm wasting time, maybe it will help someone. Regardless, the info will be out there.

I asked B&W about it; They said it was built for an OEM customer and everything was IP thus no info *at all*. I noticed the driver board had a RS232 10-pin and a JTAG.... Maybe need to spend a few minutes with those ports.

[drlava]

Hi guys, the title of this thread should be 'internals of that B&W Tek CNI 10mW ebay 473nm laser' probably more people would read it and chime in. Just saw it now. Anyway, I've already done the conversion of one to analog modulation. The pot you were adjusting is the optical output setpoint. This is why it didn't have any effect when you removed the pickoff sensor, it just ramps to max current. There is another adjustment (not sure which pot yet) that sets the maximum pump current. On mine this was set to 1.95A. I also have written down some of the pinout for the head connector, I can post tomorrow. I'll be great if we can figure out which pot does what. This is a start.
Good pictures so far.

[mophead]

Sweet, Andrew.

I hadn't intended for the thread to go this way, but hey, why not? There are a few of these units out there, seller might have some more (functioning or not).

I ourta run take some pics {EDIT-- will get good macro pics tomorrow. Don't have good lighting here.} Maybe start a new thread?

[Kyle]

This arrangement is typically due to the use of an anamorphic prism pair for bump beam correction. There is probably a pair inside the black cylinder just after the pump diode, but it could also be some sort of other arrangement as well. It's hard to tell for sure without seeing inside the cylinder..

Also, to answer the OPs question, every blue DPSS laser I've seen personally has the LBO encased in a teflon container inside the laser head to protect it from moisture.

Ah, that makes sense. At first glance I thought the Nd:YAG itself might have been some type of prism. I'll be sure to take a closer look at the first black cylinder the next time I open the laser head up. Thanks!

Sorry guys...its BiBo. The case is to proved a layer of protection from stray I/R and damage when assembled. The cavity is aligned in a fixture at the factory and set aside with the others in the line. They just drop in the cavity as a module component and align the pump spot....temp tune and off it goes. While no where that simple or fast, but it conveys the message. The anomorphics are coated and serve well for other purposes...The optics for beam compression/expansion are still in testing when I have time. Good for parts...the flaky ones...diode is a good transplant after a GRIN or FAC install.....2 watt unit....based on output levels from factory settings. Driver is good for up to 4 amps....

Thanks MechEng3, very informative! That does seem to be a simpler way to mass produce these blue DPSS lasers.

A quick Google search shows that BiBo is generally more efficient than LBO and is not hygroscopic. In these Chinese DPSS units where the cavity isn't airtight it makes sense to use it over LBO, although I was under the assumption that BiBo was more expensive than LBO.

So within the white container lies the high reflectance mirror, BiBo crystal and the output coupler? I noticed on my unit that the beam exiting the crystal was hitting the side of the container, any idea on how difficult it would be to realign? Could it be a matter of simply changing the angle or position of the crystal housing?

Hi guys, the title of this thread should be 'internals of that B&W Tek CNI 10mW ebay 473nm laser' probably more people would read it and chime in. Just saw it now. Anyway, I've already done the conversion of one to analog modulation. The pot you were adjusting is the optical output setpoint. This is why it didn't have any effect when you removed the pickoff sensor, it just ramps to max current. There is another adjustment (not sure which pot yet) that sets the maximum pump current. On mine this was set to 1.95A. I also have written down some of the pinout for the head connector, I can post tomorrow. I'll be great if we can figure out which pot does what. This is a start.
Good pictures so far.

Thanks drlava, good info and good ideas. I was thinking about using a FlexMod to drive the diode after I got the beam cleaned up and the output a little higher. Were you able to just connect the diode to the FlexMod and use the original TEC driver?

As far as the pot, that's what I was thinking, so that's good to know.

From my fiddling it seems that the pot closest to the center of the board controls the diode current, because on my unit the affects of adjusting that pot were seen nearly immediately. Turning this pot about two revolutions with the pickoff sensor in place yielded approximately 50% higher output.

I have a version 4.0 board, so I'm assuming the last pot must control the temperature of the BiBo crystal. Surely it wouldn't be diode temperature as it seems the temperature of the doubling crystal is more important.

I'm hoping I didn't burn the coating of the BiBo because I noticed a little extra scatter in the beam after adjusting the center pot. Oddly enough the beam has stayed in an ovular near-TEM00 mode but the pattern of the new scatter will fluctuate slightly during warm up. I'm thinking this fluctuation may have been present all along and I just haven't noticed it before.

Cool, thanks guys.

I'm going to take some hi-res macro shots of everything in the cavity and the driver boards too. Not sure they will be up tonight, but they are comming. Also going to try and pinout the head and post it up as well.

Maybe I'm wasting time, maybe it will help someone. Regardless, the info will be out there.

I asked B&W about it; They said it was built for an OEM customer and everything was IP thus no info *at all*. I noticed the driver board had a RS232 10-pin and a JTAG.... Maybe need to spend a few minutes with those ports.

Sweet, Andrew.

I hadn't intended for the thread to go this way, but hey, why not? There are a few of these units out there, seller might have some more (functioning or not).

I ourta run take some pics {EDIT-- will get good macro pics tomorrow. Don't have good lighting here.} Maybe start a new thread?

mophead, I'm very sorry for derailing your thread! I jumped in because I had just opened my laser up and felt like providing a few pics so that you could possibly get an idea of the wiring layout, etc of the head before you took the risk of opening your unit. And many thanks for speaking to B&W about these lasers, I had figured they wouldn't want to disclose too much but it never hurts to ask.

I did see on B&W Tek's web site that they do sell some sort of computer interface for these lasers. Maybe that is what the RS232 and JTAG connectivity is for.

I can't wait to see some good macro shots of the cavity! Should be interesting.

Thanks again to all.

- Kyle

[300EVIL]

Sorry guys...its BiBo. The case is to proved a layer of protection from stray I/R and damage when assembled. .

You sure about that? I'm pretty sure that case is there mostly for thermal reasons.