A space-borne ultra-stable laser system with an excellent long-term frequency stability for gravitational wave detection

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.