Laser Controller for Space Applications

Ground and space-based telescopes are often calibrated using a network of “standard stars” that are used as reference points. Currently, astronomers use the star ‘Vega’ as a reference point for calibration; however, modern methods such as the use of an artificial star are needed to increase the accuracy of the calibration. The goal of this project is to design a high precision laser controller to be flown on a spacecraft, which will provide a reliable and accurate laser light source to serve as an artificial star reference point for telescope calibration. Given the intended use of this laser controller, its error must be extremely low. Otherwise, fluctuations in the laser may cause improper calibration of the telescopes. This project aims for a percent error of less than 0.25% for the controller. Factors that can cause fluctuations in the laser output are temperature as well as the current supplied to it. This laser controller will be used to calibrate telescopes that detect and analyze exoplanets and black holes, including the GMU telescope.

My name is Lina Alkarmi and today I’ll be presenting my fall 2022 research project which is a laser controller for space applications. Many ground and space-based telescopes use a network of standard stars that are used as reference points, however these reference points have been identified back in the 1970s, so modern methods are being researched to increase the accuracy of this calibration. An example is using an artificial star which is just a controlled reference point rather than using actual stars. This is done through laser systems. One caveat to this is that lasers are sensitive to temperature and current so you need to make sure you have a very steady temperature and current so that way you can properly calibrate everything.
The goal of my project is to design a high Precision laser controller that will be flown on a spacecraft to provide a reliable and accurate laser light source that will serve as a reference point for telescope calibration. It needs to have a very low error, less than 0.25 percent, otherwise fluctuations in the laser can cause improper calibration. This project will allow scientists to learn more about exoplanets and dark matter.
This is a block diagram of the laser controller. On the right we have the laser mock-up which will contain the laser diode, fan, the TEC which is thermoelectric cooling which will maintain the temperature, some temperature sensors, and some current sensors. We also have the laser driver to supply current to the laser and the TEC controller that will supply current to the TEC. We have 5 volts DC power and then finally everything will be interfaced with Raspberry Pi. I designed the board using kicad and printed it and soldered it. You can see the laser mock-up right here on the left. It has the thermistors, the TEC, and the fan mounted right here. The main components of the laser controller are the laser driver, the laser mock-up which will be actually the laser diode in the final Design, TEC to maintain temperature, the TEC controller, thermistors to measure temperature, and interfacing with Raspberry Pi.
Testing and Analysis was done so the thermistors measure the bottom side of the TEC and the TEC is connected to the board with the top side facing down. So when the current is non-reversed the top of the text Cooling and the bottom side is Heating, and one current is reversed the top is Heating and the bottom side is cooling. So I measured the heating and cooling of the TEC over time under different current and voltage supplies. This is an example of some of the data, so we have two thermistors and I took the average between both so they’ll give us resistance readings which correspond to temperature. Then I timed it so as time passed we had the temperature of
the thermistors. So I did this for non-reversed current and reversed current. You can see right here so on the left we have the non-reversed current; it’s heating up and then at about 100 seconds I turned off the current Supply so it’ll cool back down to room temperature. Here it went up to about 30 degrees and 100 seconds and then you can see the same thing for the reversed current temperature but now it’s cooling down and then it’ll go back up to room temperature.
So this same thing was done for 0.5 amps, everything looks about the same but it heats up a lot faster so in about 60 seconds to 38 degrees and then on the right it cools down a lot faster as well because of the higher current. And then finally the highest current supplied was 0.75 amps so it heats up in 60 seconds to 50 degrees Celsius and then for the cooling on the right it cools all the way down to about 12 degrees Celsius in 60 Seconds. So overall it was found that thermoelectric cooling can properly maintain the laser temperature and the current supplied to the TEC is used to control the heating and the cooling. Some applications of this project are calibrating telescopes that detect exoplanets and black holes, for example the GMU telescope and the observatory. Astronomers may also use the laser to calibrate their measurements of dark energy, and satellites can also use it to calibrate their instrumentation. Some of my next steps are to test the laser mock-up under different currents and voltages so that we can analyze the performance of the TEC. I’ll also be designing and testing the PCBs for the laser driver and the TEC controller. I’m going to connect everything in the end into one design and interface with Raspberry Pi. these are my sources and thank you very much for watching.