Tara heard back from the machine shop, and they can do 1/4-80 threading. I finalized the design this morning. I was sure to check whether the frequency could be sufficiently tuned, and whether the screw on the grating mount would fit into the box. After making some changes, I printed out the designs and went to the machine shop with Tara to talk about our design. It should be ready sometime next week between Wednesday and Friday. Finalized designs are on the SVN.
Frank (from the Birmingham group) emailed us back about the ECDL. He said they used the $1000 current driver from Thorlabs (http://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=10), although he recommended the $4800 Vescent current driver (http://www.vescent.com/products/electronics/d2-105-laser-controller/). He also said that there was not a good way of predicting the noise budget beyond knowing what contributes to noise at different frequency ranges:
- temperature/environmental noise at low frequencies
- acoustic vibrations at a few hundred Hz to kHz
- current noise at kHz to MHz
- relaxation oscillations of laser diode at a few MHz
Frank also said that he would be leaving the Birmingham in September and has discontinued the ECDL project, so they haven't gotten past making a working prototype. He was otherwise very willing to help.
I'm currently talking to Thorlabs to see if they can give us the current noise density instead of an RMS noise on their current driver. It seems that if we use the Thorlabs 100 mA driver (instead of the Thorlabs 200 mA driver we had been planning on), the noise is reduced a lot. At 100 mA, we should get an output power of ~75 mW from the Thorlabs diode and ~50 mW from the QPhotonics diode. This actually is probably sufficient for what we need, so the lower current input should not be a huge problem. From a range of 10 Hz to 10 MHz we have the following values:
- Vescent current driver (200 mA): 0.3 uA
- Thorlabs current driver (200 mA): 1.5 uA
- Thorlabs current driver (100 mA): 0.2 uA
Vescent current driver does much better at lower frequency ranges, and has RMS noise of 0.05 uA between 10 Hz and 100 kHz, but is comparable over a larger range with higher frequencies. While the RMS values are promising, we aren't sure how the noise density compares over the entire frequency range... I'm hoping to hear back from Thorlabs soon about this. It seems like the Thorlabs driver is an actual possibility though.
Tomorrow Tara and I are going to get started in the lab. Tara will show me around, and I'll try to get the TEC working.