A space-borne ultra-stable laser system with an excellent long-term frequency stability for gravitational wave detection
Jialu Chang, Qiyue Wu, Zhiyuan Wang, Jingxuan Zhang, Qiang Wei, W. H. Yuan, Deyuan Zhu, Jiarui Zhang, Xuying Li, Xinpeng Wu, Z. H. Lu, Jie Zhang
Abstract
Abstract Ultra-stable lasers are pivotal in various scientific applications, notably in space gravitational wave detection projects. We develop a space-borne ultra-stable laser system based on a home-made non-planar ring oscillator (NPRO) laser and an ultra-stable cavity laser stabilization system. The ultra-stable cavity is a vertically mounted 8 cm long cavity, with tunable zero-crossing temperature and low vibrational sensitivity. To make a cavity with any standard grade ultra-low expansion glass (ULE) material, and tune the zero-crossing temperature to the satellite platform temperature, we design three ultra-stable cavities with different configurations to unambiguously explore their thermal properties. The measurement results meet the design goals well, and the zero-crossing temperature of the cavity can be tuned from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>−</mml:mo> <mml:msup> <mml:mn>19</mml:mn> <mml:mrow> <mml:mstyle scriptlevel="0"/> <mml:mrow> <mml:mo>∘</mml:mo> </mml:mrow> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> C to 16.0 °C. We measure the temperature fluctuation noise through modulation experiment, and it agrees well with the theoretical simulations. The vibrational sensitivities in three directions are measured to be around 10 −11 /g–10 −10 /g. The total weight of the system is 14.0 kg, with a volume of about 18 L, and the power dissipation of the electrical system is 18.6 W. Finally, the prototype of the space-borne laser shows a frequency instability of 9.5 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>16</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> at 0.2 s, and the frequency noise is measured to be 3.6 Hz/Hz 1/2 at 6 mHz over three months, satisfying the mission targets of all current space gravitational wave detection programs.