JTK Notebook

Projects

Ti:Sapph Laser GitHub Link

Ionization GitHub Link

To see the code you'll need to be added as a collaborator. Email me at karpel@wisc.edu or josh.karpel@gmail.com and let me know the email on your GitHub account and I'll add you.

To Do

Short Term

• Assemble Ti:sapph laser

Long Term

• Build box for Ti:sapph laser

Theory

• Work through Raman System Effective Hamiltonian calculations

To Buy

• Ti:sapph cavity saturable absorber
• Blue optics (cylindrical-lens telescope, focusing lens) (maybe not necessary)
• Optical breadboard

Log

2015-9-1

• Measured diode current vs power curve. Max is 2.8 W of output power at 3 A input current.
• Drilled a hole in the top of the crystal mount to add a set screw. Slathered the inside of the hole with thermal paste, slipped the crystal in, and tightened the set screw. Crystal is held quite solidly! May still have to redesign at some point, but this will definitely work for now. Some concern over thermal paste on sides of crystal, may want to clean it off at some point.
• Aligned blue beam through crystal. Very cool! Crystal mount holds at 15 deg C easily. Possible concerns over difference between this temperature and the internal temperature of the crystal inside the beam path, but we don't have a way to measure that. Ran for ~1 hour, no visible signs of damage. Not too worried.
• Took a first run at the absorption measurement. 2.8 W in, 1 W made it through the crystal, which is 64% absorption if true - doubtful. We're only measuring transmission, so we can't be sure that the full 2.8 W is incident on the crystal. Probable pre-crystal loss mechanisms: scattering, polarization/Brewster losses (although we seem to have landed very close on our rough alignment).
• Added green dots to diode tube and mount - when the dots are lined up the output is coming out p-polarized relative to the crystal. Note that rotating the diode tube changes the beam path because I'm bad at machining, so it won't be aligned if you rotate it anyway.

2015-8-31

• Finished water chiller assembly and tested it. Many possible settings give OK performance, but I the best performance is when the water temperature is as low as possible (10 deg C), with the diode mount held at 20 deg C with the full 3 A of current running.

2015-8-14

• Last water chiller parts should arrive today.
• Working on theory/programming for the most part.

2015-8-6

• Made TEC wire connector for crystal mount. Everything is ready to be assembled when the water chiller accessories get here. Incidentally: distilled water is on the fourth floor, in the nitrogen room near the undergrad labs. There's a jug under the table in the other side of the lab.
• Apparently Ann did not actually submit the mirror purchase order because my email title was not specific enough for her to look at (wtf...). Issue is resolved, order has been placed.
• Started writing up some notes on Ti:sapph stuff in LaTeX.

2015-8-5

• Zach Simmons passed his thesis defense. Huzzah!
• Ordered water chiller accessories. Should be here in two days?

2015-7-30

• Talked to Ann about the missing Thorlabs order and water chiller. Looks like she never processed the requests - issue is now resolved.
• Started working through the theory in Appendix A of Josh's thesis.

2015-7-29

• Started finalizing Gaussian Beam Tools v4.0 (commenting, examples, etc.)
• Worked with David on wrangling the cavity lock. Maybe works a bit better than before, but still not great (messy output, still no Stokes beam). Did get better output power (100 mW with vacuum, ~60 with .2 atm of D2).

2015-7-27

• Started digging into SESAMs. Got OK to buy a SESAM (centered on 800 nm), but I sent an email to the diode pumping paper people to see how they sourced their broadband SESAM. They're in England, so it may take a day or two to get a reply.
• Drilled holes for water block on diode mount. Managed to break the tap off in the second hole, rendering it totally unusable. Plan is to screw it down using only one hole. Ugh...
• Talk to Deniz and David about how to tune the Ti:sapph - looks like it's done via an aperture between the second prism and the output coupler. Will need to think about what kind of aperture to use (knife-edge?, must be on translation stage to move back and forth). Tunable is a good first step before mode-locking - proof of concept, make sure we can see the output, etc.

2015-7-24

• BATOP got back to me - all their products are just stock stuff, apparently, not very open to custom orders. Reflekron's person is on vacation, apparently. Wonderful.

2015-7-23

• Sent emails to two places that sell SAMs. Don't seem to be many places...
• Worked on Gaussian Beam Tools v4.0.

2015-7-22

• Did presentation in group meeting.

2015-7-21

• Pulled the trigger on the mirror order from Lambda.

2015-7-20

• Worked on Gaussian Beam Tools v4.0.
• Worked on Ti:sapph group meeting presentation.

2015-7-16

• Talked about final mirror order with Deniz. Decided on 10 mirrors (2 R = 10 cm curved, 2 R = 7.5 cm curved, 4 flat, 99% output coupler, 98% output coupler). Emailed Lambda for another quote request and with a few more questions (not that they've responded to my last email...). Definitely need to know what they mean by "high reflectance" - we want to minimize cavity losses to make the laser more efficient. The diode pumping papers I'm working off quote 0.7% cavity losses (Finesse is around 900).
• Emailed ECI for the revised quote as well. I imagine it will be very expensive.
• Completed NSF RCR training.
• Emailed Reflekron about a SESAM.
• Started writing Gaussian Beam Tools v4.0.

2015-7-15

• Found a stable Z cavity with a folding angle of 10 degrees, a total length of about a meter, and plenty of stability room to move the FS prisms around in. Will require tuning once it's operating to get the crystal and prisms positioned right. Need a way to do an interferometric measurement of the pulses to analyze the GVD compensation?
• Incidentally, fixed (all of?) the KeyError problems by naively upscaling all the units (so that it's not working with such small floats all the time) and adding the keys to the position list. There's now a small problem where, in a cavity, it's possible that the endpoint of the position list will not be exactly where you wanted it to be, throwing off the symmetry of the calculation. Increasing the unit upscaling seems to help. Also, wrote a neat waist detection algorithm. Now have to rewrite a bunch of older code to use that. Maybe just save it for v4...

2015-7-13

• Emailed Lambda back with more questions re: mirrors.
• Realized we need to use a Z cavity instead of a bowtie cavity so that we can use a prism pair for GVD (Group Velocity Dispersion) compensation. Started looking at cavity stability and how prism pairs work as GVD compensators.
• Decided I probably need to massage the code a little to avoid running into key errors because of floating points. Will probably recode everything so that it works in tenths of a millimeter as the "base unit" instead of meters, so that everything can be an int. My other thought is to simply add the dictionary keys to the position list - this would effectively decouple the position list resolution from the optical element positions, which would be very nice anyway (it would let you make things like cavity length scans at higher resolution than currently works). Still worried about floating point key errors with that method though. Maybe a combination....

2015-7-10

• Finished Gaussian Beam Tools v3.2, which reimplements existing cavity stability analysis MatLab code.

2015-7-8

• Tried to get some mill time today, but all the machines were full. Not urgent, so I'll let it calm down a little.
• Started making slides for talking about the Ti:sapph laser to the group.
• Watched over David's shoulder while he tried to get the cavity lock behaving better.
• Started writing Gaussian Beam Tools v3.2, which will re-implement my existing cavity analysis MatLab code.

2015-7-7

• Sent out Gaussian Beam Tools v3.1, with fixes for issues running on Mac.

2015-7-6

• Gaussian Beam Tools v3.0 is done. Sent it out. Nick found that there were some problems with running it on Mac. Will fix issues and send out v3.1 tomorrow.

2015-7-2

• Wrote some code to back out q values from measured beam parameters. Mode Matching v2 is basically done now - it replicates all of the functionality of David's code and expands it a bit by letting you use it in a "plotting" mode with no mode matching, and by letting you work with any number of lenses.
• Thinking about v3: replace lenses with optical elements as classes, handle the position rail better (maybe a class of it's own?). Basically use classes to generalize and expand what the code can do.

2015-7-1

• Continued working on Mode Matching v2.
• Heard back from ATF on mirror quote. Order is too small and specialized for them to do...

2015-6-30

• Wrote v2 of the mode matching program from scratch with some new ideas. Worked great on the first try!

2015-6-29

• A bit downtime for the next week and a half while the student shop is closed. Decided to write a program to do mode matching. Wrote v1 today, and it was awful and didn't work at all.
• Ordered the copper part of the crystal mount from eMachineShop. ETA ~3 weeks.

2015-6-25

• Got quote back from ECI - $13000! Way too expensive. Asked them to redo quote without the backs AR-coated to see what that's like. Sent quote request to Lambda.

2015-6-24

• REO got back to me and said they don't do mirror quotes for such small orders. Sent a quote request to ECI.
• ECI got back to me within 30 minutes with questions. Now that's what I call customer support...
• Made aluminum part of crystal mount.
• Haven't heard back from ATF on mirror quote or eMachineShop on copper part. It's not like it's their job or anything....

2015-6-23

• Got in early to do some machining but all three mills were already being used...
• Sent passive-aggressive emails following up on the mirror quotes.
• Got a quote on indium foil. Sent in purchase request.
• Started working through Raman system theory.
• Heard back from Advantech Machining. They won't do such a small job.

2015-6-22

• Ordered TEC, thermistor, and Kapton tape from Thorlabs. Ordered new mount from Newport. Ordered water chiller from eBay. Ordered aluminum from the stock room to make the aluminum part of the crystal mount.
• Asked for a quote on indium foil.
• Asked for quotes on making the copper part of the crystal mount from eMachineShop and Advantech Machining.
• No response on any of the mirror quotes except the questions from Layertec. Will send passive-aggressive emails tomorrow.

2015-6-18

• Realized the whole mounting scheme won't work because the Thorlabs rotation/translation mount is too large. Will rework design tomorrow to use this mount instead. Will likely have to buy more aluminum and copper stock (gdosafjoijforngoasjf). May look into getting the copper part of the mount outsourced - it's going to involve fairly precise machining on a small piece, and the shop will be closed for a week and a half anyway. The aluminum part I'll do next week.

2015-6-17

• Cut channel into diode laser mount. Waiting to drill screw holes until I get the part to see if I need to mill any more out to make it fit.

2015-6-16

• Got questions back from Thomas at Layertec. Sent answers. They're working on a quote.

2015-6-15

• Ordered water blocks from Custom Thermoelectric.
• Ordered rotation/translation mount from Thorlabs.
• Designed channel cut for diode laser water cooling modification. Looks like it should work with no problems...
• Designed crystal mount.
• Ordered crystal mount copper/aluminum stock.

2015-6-11

• Talked to Deniz about lasing direction. Decided we don't need an intracavity isolator for the Ti:sapph laser. The output coupler will provide enough asymmetry to force lasing in the correct direction.
• Sent email to Layertec requesting quote for Ti:sapph cavity mirrors.
• Talked to Zach about design for Ti:sapph crystal mount. Decided on basic design using water block, possibly from Custom Thermoelectric. Crystal should probably be wrapped in thin indium foil for better contact with copper. Also talked about cutting a "channel" out of the diode laser aluminum block to add a similar water block below the TEC.