Space-based gravitational wave needs prototype Laser Detectors

Space-based gravitational wave needs prototype Laser Detectors 

The Laser Interferometer Space Antenna (LISA) is a kind of prototype laser. It is set at the center of the first space-based gravitational wave observatory. Researchers outlined for LISA's instrumentation in a way that the new laser can meet nearly all the crucial requirements. It has been an important step in bringing the successful accomplishment of the observatory program. 

Steve Lecomte said, "What a motivating challenge it was to realize a laser system with state-of-the-art performances, capable of meeting the stringent reliability requirements of a space mission." He works with CSEM, a Swiss research firm. He demonstrated the detail performance of the prototype at The Optical Society's (OSA) 2019 Laser Congress in Vienna, Austria. The program held from 29 September to 3 October.   

The U.S. National Science Foundation (NSF) has funded earlier ground-based gravitational-wave detectors. One of them is Laser Interferometer Gravitational-wave Observatory (LIGO). LISA is able to cooperate with LIGO by deploying a gravitational wave detection system in space. LIGO is the first observatory to observe the direct observations of gravitational waves. In his general theory of relativity, Albert Einstein predicted the ripples in the fabric of space and time more than 100 years ago. NSF has confirmed that LIGO has identified the ripples in the spacetime fabric.  

Both the LIGO and LISA are dependant on the laser. Lasers help them to detect gravitational waves. Any gravitational wave detector requires precision and reliability. Long-term use in space is another criterion for the lasers used in the LISA mission. When it can meet all the needs it gives the best result to detect gravitational waves. 

The mission of LISA is mainly led by the European Space Agency (ESA). The U.S. National Aeronautics and Space Administration (NASA) provided a helping hand to ESA on this mission. 

According to the future plan, LISA is scheduled to launch its expedition in the 2030s. It will have three spacecraft in a triangle shape. They will travel millions of kilometers across. By relaying laser beams back and forth, the spacecraft will study their signals. It helps them to find evidence of gravitational waves.  

The LISA system contains a multitude of components and they must work together to complete the mission successfully. For this reason, the laser must maintain all its standards. Power output, wavelength, noise, stability, purity is some of the parameters that should be double-checked before the expedition. 

The joint collaboration of ESA and NASA has resulted in developing a laser that is able to meet almost all the requirements. The system consists of both optical and electrical components. The latest technologies are used to make these space-grade components so that they can cope with the space environment.  

The seed laser is the starter of the system. It is a kind of packaged self-injection and it is locked. It helps in realizing the mission-specified wavelength of 1064 nanometers. The seed laser emits light and it is injected into a core-pumped Yd-doped fiber amplifier (YDFA). The amplifier than accelerates the average power from 12 to 46 milliwatts. The optical reference cavity works on the directed fraction of the amplified light. It follows the orders of magnitude to improve the spectral purity and stability of the laser.  

The phase-modulator is the pathway that is used by the main part of the light to cross. It is done to add features allowing the mission to compare the signals coming from the three spacecraft. The whole process is known as interferometry. There are also other YDFA. They are second core-pumped YDFA and a double-clad large mode area YDFA. They amplify the signal to almost 3 watts. 

The research team needed a special station to assess how the prototype laser system works. They created the station to see the prototype laser system’s performance. As a part of their experiment, the team used an optical frequency comb, a cavity-stabilized ultra-narrow 1560 nanometer laser, temperature-stabilized low-drift photodetectors, and an active H-maser to measure the stability of the system's frequency and amplitude.

The full frequency ranges from 1 megahertz and above 5 megahertz. During the tests, all the LISA specifications compliance was demonstrated in that range. There were exceptions below or over that range. The problem regarding the noise was also considered. The team has also found the minor deviations from the specifications. They have found the causes and have found probable solutions to modify the system. According to these solutions, some technical modifications are needed to improve the seed laser.   

 Lecomte said, "While a launch date shortly after 2030 might appear far away, there is still substantial technological development to be performed. The team is ready to further contribute to this exciting endeavor."