Tip-tilt retrieval using trilateration of a sodium laser guide star

Area of Science:

• Optical astronomy
• Adaptive optics
• Optical communications

Background:

• Tip, tilt (TT) and focus modes are crucial for optical communications but difficult to measure directly using laser guide stars (LGS).
• Residual TT errors in ground-to-satellite optical links cause beam wander and signal fades.
• Accurate TT measurement is essential for effective pre-compensation in laser communication systems.

Purpose of the Study:

• To develop and evaluate a method for full tip, tilt (TT) retrieval solely using laser guide stars (LGS).
• To assess the feasibility and required technological advancements for this TT measurement technique.
• To improve the performance of ground-to-satellite optical communication links.

Main Methods:

• Utilizing trilateration with differential arrival times of a pulsed LGS at multiple detectors.
• Determining LGS position to derive TT from the uplink path.
• Simulating the method's performance with specific detector timing resolution and photon collection rates.

Main Results:

• The proposed method can retrieve tip and tilt modes with an accuracy of approximately 0.45 arcsec.
• Achieved accuracy requires a detector timing resolution of 10^-12 s and photon collection rates of at least 10^8 photons/s.
• Pre-compensation using this LGS-based TT measurement can increase received power by over 2 dB for low Earth orbit (LEO) satellite links.

Conclusions:

• The trilateration method enables accurate full tip, tilt (TT) retrieval using only laser guide stars (LGS).
• This technique offers a viable solution for mitigating TT errors in optical communication systems.
• The method promises significant improvements in received signal power for ground-to-satellite laser communications.