JOKARUS—An optical absolute frequency reference on a sounding rocket based on molecular iodine

We present the JOKARUS payload, which was launched aboard the TEXUS 54 sounding rocket mission in May ’18. It demonstrated the first iodine-based optical frequency reference in space, using a frequency-doubled 1064 nm diode laser for Doppler-free saturated-absorption spectroscopy of the R56(32-0) transition in molecular iodine. In ground-based operation, this optical oscillator provides a fractional frequency stability of 4 ⋅ 10-13 at an integration time of 1 s. During the 15-minute flight, the laser frequency was measured by an optical frequency comb, confirming autonomous operation as an absolute frequency reference in space