LIGO Mirror Birefringence Testing
Faculty Mentor Name
Ellie Gretarsson, Andri Gretarsson
Format Preference
Poster
Abstract
Ever since the discovery of lasers in 1958, measurements - most notably those that use interferometry - have greatly advanced. Interferometry is the process of measuring or observing certain quantities/qualities through the use of interference of waves. Since light is a wave and lasers are simply and very focused and directed source of light that is very well characterized and controlled, the use of lasers in interferometry was quickly used as the new standard wave source. Laser Interferometer Gravitational-Wave Observatory (LIGO), as its name implies, is an interferometry device that uses the interaction of lasers with itself to observe the presence of gravitational waves. LIGO is, in its simplest form, a pair of multi-kilometer L-shaped arms in which a laser is split, sent down each end, reflected off a mirror, and then reassembled as one beam. Gravitational waves, initially implied by special relativity, act on space as a form of shear, causing a slight distortion that is normally imperceptible. By measuring its effects on the laser and how much it is shifted from its original path/set distance, these waves can be seen in the non-perfect reconstruction of the lasers as they interact with each other destructively or constructively.
Due to the very high sensitivity required to detect the minute effects of gravitational waves, LIGO requires very well-behaved lasers and mirrors. How well-behaved a mirror is dependent on the amount of “noise” associated with the reflection, where noise is additional meaningless information that either makes the detection of waves impossible or very difficult. To this aim, mirrors must be extremely well behaved as even the thermal noise, noise made from the vibratory modes of molecules as a result of thermal energy, can significantly impact the collected data. Aluminum Gallium Arsenide (AlGaAs) mirrors have shown promise in lowering the detectable thermal noise for use in LIGO. Traditional glass mirrors have worked well in the past due to them being amorphous, where amorphous means it has no internal repeating structure, they do not exhibit birefringence however AlGaAs mirrors do. Birefringence is the property of optically anisotropic materials, partially crystals. Birefringence affects the polarization of light as it reflects or refracts in such materials. AlGaAs mirrors are built as singular crystals using ALD (Atomic Layer Depositions) and then deposited on a substrate to maintain their structure. Since they are built as a singular crystal with repeating internal structure, AlGaAs mirrors exhibit a non-negligible amount of birefringence, and therefore, it must be studied before its implementation in LIGO.
LIGO Mirror Birefringence Testing
Ever since the discovery of lasers in 1958, measurements - most notably those that use interferometry - have greatly advanced. Interferometry is the process of measuring or observing certain quantities/qualities through the use of interference of waves. Since light is a wave and lasers are simply and very focused and directed source of light that is very well characterized and controlled, the use of lasers in interferometry was quickly used as the new standard wave source. Laser Interferometer Gravitational-Wave Observatory (LIGO), as its name implies, is an interferometry device that uses the interaction of lasers with itself to observe the presence of gravitational waves. LIGO is, in its simplest form, a pair of multi-kilometer L-shaped arms in which a laser is split, sent down each end, reflected off a mirror, and then reassembled as one beam. Gravitational waves, initially implied by special relativity, act on space as a form of shear, causing a slight distortion that is normally imperceptible. By measuring its effects on the laser and how much it is shifted from its original path/set distance, these waves can be seen in the non-perfect reconstruction of the lasers as they interact with each other destructively or constructively.
Due to the very high sensitivity required to detect the minute effects of gravitational waves, LIGO requires very well-behaved lasers and mirrors. How well-behaved a mirror is dependent on the amount of “noise” associated with the reflection, where noise is additional meaningless information that either makes the detection of waves impossible or very difficult. To this aim, mirrors must be extremely well behaved as even the thermal noise, noise made from the vibratory modes of molecules as a result of thermal energy, can significantly impact the collected data. Aluminum Gallium Arsenide (AlGaAs) mirrors have shown promise in lowering the detectable thermal noise for use in LIGO. Traditional glass mirrors have worked well in the past due to them being amorphous, where amorphous means it has no internal repeating structure, they do not exhibit birefringence however AlGaAs mirrors do. Birefringence is the property of optically anisotropic materials, partially crystals. Birefringence affects the polarization of light as it reflects or refracts in such materials. AlGaAs mirrors are built as singular crystals using ALD (Atomic Layer Depositions) and then deposited on a substrate to maintain their structure. Since they are built as a singular crystal with repeating internal structure, AlGaAs mirrors exhibit a non-negligible amount of birefringence, and therefore, it must be studied before its implementation in LIGO.