Alignment of CTH: YAG and Alexandrite cavity mirrors

[Laser Ben]

I am working on a project for the Intel Science Fair. I am demonstrating using 435nm LEDs to excite CTH YAG and Alexandrite to create a CW laser. I have already gotten my CTH YAG and mirrors for it thanks to Steve Roberts here and I recived a very nice new set of Alexandrite mirrors from Piotr here! Thanks Guys!

I am really interested to find out the proper way to align the cavity. All of the mirrors are flat, and the cavity length will be approximately 6 inches in length. The Crystal being pumped is centered in the cavity and the clear ends are 3x3mm.

I do not know if the HeNe method will work well for this project as it is absorbed by both mediums. What would you guys recommend for aligning the mirrors?I can most likely get a hold of any specialty equipment for aligning it, so if there is a really easy way to align it that works better, let me know.

Thanks!

[mixedgas]

[quote
I am really interested to find out the proper way to align the cavity. All of the mirrors are flat, and the cavity length will be approximately 6 inches in length. The Crystal being pumped is centered in the cavity and the clear ends are 3x3mm. end quote ]

Are you sure the mirrors I sent you are flat?

you have a choice of a laser or autocollimator.

Steve

[Laser Ben]

Steve,

I checked the mirrors on a optical flat with a monochromatic light like you suggested, they are flat for sure.

How would I do it with a laser and what wavelength would I need?

[mixedgas]

How would I do it with a laser and what wavelength would I need?[/QUOTE]

see:


http://www.st.northropgrumman.com/sy...e_absorpti.PDF -

http://www.st.northropgrumman.com/sy..._YAG_graph.pdf

print the above on a paper and a transparency and overlap them and pick a wavelength

Doubled yag looks good.... Green henes dont mind back reflections.


make a centering disk with a hole in it for each end of the rod, align the alignment beam down the rod centers with the disks, adjust the beams back to the alignment laser. Warning, some lasers do not like back reflections. Make sure the alignment laser is at least 10-20 cavity lengths from the solid state cavity.

Steve

Steve

[Laser Ben]

I thought I would offer a status update.

Northrop Grumman was kind enough to cut, polish, and coat all of the crystals I needed for my project at no cost. I am getting 2 pieces of each material, Alexandrite and CTH YAG in 3x3x5mm crystals.

The LEDs have been donated from Lumileds, they are 4x1 arrays of 1mm square die. They are high power 435nm LEDs used in the newest production test samples as pump units for white LEDs. I am expecting to get ~5 watts of optical power out.

Today I got a response from Thorlab's Executive Director of Sales offering to pay for the hardware (Breadboard, Kinematic mounts for cavity).

I also machined out the mounts for the crystals yesterday. The pictures don't show the completed ones, however they are now finished and the mount area for the crystal is only the length of the crystal to allow for full access to the crystal faces for the beam. I made two so I can put one of the crystal types in each. Hopefully when the crystals return from NGC I will be able to put everything together and use Steve's alignment method.

[dar303]

Wow, impressive project! Nice to see that you are getting on with it and make good progress, we will stay tuned!

[mixedgas]

Ben, remember, single pass gain measurements are your friend. Make friends with a university prof that has a tunable IR rig, they are all over the place in California, if it doesnt lase, you can always measure gain. You run the risks of below threshold, unable of being able to detect a weak beam, or wrong optics. Single pass gain works for any of these problems.

How did you have the rod ends coated? HR, OC or AR? Please say AR!

Calculating laser medium pump, saturation,and cavity optics transmission are best done from simple math in Silfvasts book on lasers.

[Laser Ben]

Hi Steve,

Could you help explain the gain calculations? I was reading the section in the book about gain and population inversion, however, it was way over my head. Could you show me basic gain calculations?

I did get the coatings done in AR.

[mixedgas]

Some time by end of business day tomarrow I'll get back to you.

Right now I'm putting out a bunch of finanical fires.

Steve

[Laserman532]

Some time by end of business day tomarrow I'll get back to you.

Right now I'm putting out a bunch of finanical fires.

Steve

Must be nice to be able to just burn money all day long