Updates from the past few days... (sorry I forgot to elog but I've been keeping notes in my notebook)
__Monday 6/17__
I met with Tara to discuss how to get started. In order to create a useful ECDL, it must be capable of meeting the noise requirements of the experiments it is being used for. Thus, we need to see the possible experiments that we could perform to test our ECDL and choose which would be the best goal to aim for this summer. I created a power spectral density (PSD) noise plot of various experiments performed at LIGO and some noise plots from ECDLs created by other research groups. We decided to use the crackle experiment as our standard since it has the highest noise requirement and thus will be easiest to achieve at first.
List of things to order (links):
__Tuesday 6/18__
General SURF requirements: I attended laser safety training for class 3b and class 4 lasers in the morning. I attended orientation activities for SURF for the latter half of the afternoon.
In terms of my project: I remade the PSD noise plot in Matlab since this is the language I will be using (attached). The next step is to determine how to design the ECDL so that the noise requirements from the crackle experiment can be met. I met with Tara and discussed how to start doing noise calculations using the 1982 Saito paper as reference.
__Wednesday 6/19__
I attended the LIGO internal orientation and general safety training as part of the SURF requirements. Then, I continued to try to perform the noise calculations. My noise calculations will need to take into account intrinsic noise of the laser due to current and temperature fluctuations. The noise is then decreased by some factor determined by parameter X (from Saito paper) by the external cavity. I am starting with the parts from Monday's list to see if they can be arranged in a way that meets the noise requirements. I was able to determine that parameter X for a setup with 10 cm between the laser and the grating will be about 71.
I sat in on Rana's weekly talk to the graduate students, since Tara thought he might discuss phase lock loops (PLL) which I may need to measure my frequency stabilization later on.
__Thursday 6/20__
Dr. Weinstein gave a talk for the LIGO SURF students today about the basics of LIGO. He discussed the general significance of gravitational waves, how gravitational waves are generated by pulsars, and some basic interferometry to explain how LIGO works.
I spent the morning trying to figure out how to convert the calculations I have into a final linewidth and average PSD. Tara wasn't sure how to do this so I emailed Dmass about how to do this... he suggested I estimate the bandwidth of my noise (where the signal from noise would disappear) and go from there. **Using a bandwidth of about 1 GHz, I find that the linewidth after going through the external cavity should be about 12 kHz (which represents a noise level of 0.15 Hz/rtHz). This is well below the 300 Hz/rtHz that is required for the crackle experiment. Assuming that there will be noise from other mechanical sources, this seems reasonable... I think I can maybe order parts soon? I will check my calculations again tonight to make sure there aren't any glaring errors. Maybe the bandwidth of the noise signal I used was too small, I'm not positive yet. I will write this up nicely so that I can post it here, maybe later tonight. ** |