Radiation-induced degradation of low noise quadrant photoreceivers for LISA

The optical signals of the three LISA interferometers (long-arm, reference, and test-mass) on each optical bench are detected by opto-electronic devices named Quadrant Photoreceivers (QPRs). Each QPR features three main components: (1) an InGaAs quadrant photodiode (QPD) with four segments; (2) front-end electronics (FEE) incorporating a transimpedance amplifier; (3) mechanical enclosures for the previous two. QPR components have already been developed by LISA Consortium members from the Netherlands, Japan, and Germany, yielding QPR prototypes satisfying the low equivalent input current noise requirement of <2 pA/ÖHz over a 5 to 25 MHz bandwidth. During the nominal and extended mission lifetime (6.5 and respectively 12 years), the LISA QPR will be subject to different types of radiation, particularly protons from solar flares. This particularly harsh environment can cause temporary or permanent degradation of electrical characteristics due to a total non-ionizing dose (TNID). To guarantee the long-term functionality of the LISA QPDs, degradation of performance caused by radiation needs to be understood to be able to prevent/delimit radiation damages. For such purpose, a proton irradiation campaign of various LISA QPDs is planned for September 2022, using the MEDYCIC cyclotron facility of the Mediterranean Institute of Proton therapy, Centre Antoine Lacassagne (Nice, France). The irradiation plan includes proton energies of 20 MeV and 60 MeV and fluence levels corresponding to those to be experienced by the QPR during the LISA lifetime mission. The QPR radiation test plan includes various measurements of the performance before and after irradiation, such as dark current vs bias voltage and temperature, capacitance vs bias voltage vs frequency, equivalent input current noise vs. frequency, and FEE gain. Different QPR prototypes have already been benchmarked prior to irradiation. This talk will give a summary of these results, as well as a look over the tests planned during the September irradiation campaign. This work is primarily carried out by teams from Observatory de la Cote d'Azur (Nice) and ONERA Lab (Toulouse), and in collaboration with the LISA QPRWG.