CH4 AND CO2 IPDA LIDAR MEASUREMENTS DURING THE COMET 2018 AIRBORNE FIELD CAMPAIGN

In order to measure the two most important anthropogenic greenhouse gases CO2 and CH4 by means of the integrated path differential absorption (IPDA) lidar technique, stringent requirements with respect to the frequency stability of the transmitter need to be fulfilled In order to measure and optimize the frequency stability of the on-line and off-line wavelengths of an airborne IPDA lidar, a compact optical frequency comb (OFC) was for the first time employed and its performance characterized on board of an aircraft. This compact and rugged device could successfully been operated under tough in-flight conditions. Previously, such measurements were only possible in the laboratory

Pulsed optical timing distribution system with sub-ps accuracy for applications in geodesy.

Here we report on the recent progress of the highly stable optical pulsed Timing Distribution System (TDS) commissioned at the geodetic observatory in Wettzell (Germany). The system connects a master clock (H-maser) to a mode-locked femtosecond-laser, which in turn uses delay compensated fiber lines for the coherent transmission of time and frequency. In order to use time itself for sensitive delay compensation, we developed a new generation of electronic interfaces for the generation and distribution of Pulse-Per-Second (PPS) signals with sub-ps stability, a low temperature coefficient (1ps/°C) and a constant delay with respect to the master reference. For the interfacing to the respective measurement systems, a set of required standard RF-Signals (5, 10, 100 MHz) with low phase noise (-160 dBc/Hz at 10kHz) and high fractional frequency stability (Allan Deviation 8x10-14 in 1s) are provided. This indicates that the system indeed distributes the stability of the master clock without penalties, which is equivalent to having a true copy of the master clock in perfect synchronization at each end point

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 spac

Iodine Frequency Reference on a Sounding Rocket

Frequency-stable laser systems are a key technology in precision experiments and have recently become applicable in space. Optical frequency references based on cavities, atoms, or molecules allow for precise laser frequency stabilization and thus enable, for example, high-precision laser ranging in space missions. Examples are the gravity recovery and climate experiment-follow-on (GRACEFO) mission [1,2] that was recently put in operation, the planned laser interferometer gravitational wave observatory LISA [3], and future global satellite navigation systems based on optical clocks [4,5]. In the context of these and other missions, frequency references based on optical cavities [6,7] and unequal-arm-length interferometers [8,9] have been developed as compact, ruggedized instruments for application in space, featuring good short-term instability. One way to also realize low long-term instability is the stabilization to atomic or molecular transitions, providing an advantage in accuracy over relative frequency references. Together with optical frequency combs, such absolute references can further be operated as optical clocks with instability relevant for global navigation satellite systems (GNSS). Several such systems are under *[email protected] investigation today at various wavelengths, based on thermal calcium beams [10–12] or hot vapor cells using single- [13] or two-photon transitions in rubidium [14,15]. Another, already matured frequency reference is based on saturation spectroscopy of molecular iodine using the second harmonic of the narrow linewidth Nd:yttriumaluminum- garnet (YAG) laser at 1064 nm. These systems rely on the modulation-transfer spectroscopy (MTS) technique applied to the rovibronic transition R(56)32- 0, featuring narrow transitions with a natural linewidth of 300 kHz [16]. The hyperfine spectrum of this transition was studied in detail [17], the absolute frequency was accurately measured with an uncertainty of 1.1 kHz by Nevsky et al. [18], and Ye et al. demonstrated operation of a molecular iodine optical clock over the course of a full year [19]. In the past decade, several groups realized compact and portable iodine references with fractional frequency instability in the low 10−15 regime [20,21] and subjected their setups to environmental tests [22]. We believe that, using available technology at 1064 nm, developed in the context of the LISA and the GRACE-FO mission and established in satellite laser communication terminals, such systems can be developed for spaceborne instruments on relatively short time scales. Here, we present a stand-alone iodine frequency reference at 1064 nm, named JOKARUS, that is based on a microintegrated extended-cavity diode laser (ECDL) 2331-7019/19/11(5)/054068(9) 054068-1 © 2019 American Physical Society KLAUS DÖRINGSHOFF et al. PHYS. REV. APPLIED 11, 054068 (2019) [23,24] in a master oscillator plus power amplifier (MOPA) configuration. JOKARUS was built to demonstrate the maturity of our technology and its applicability in space missions. To this end, we operate JOKARUS on a sounding rocket mission and thereby prove the autonomous operation of an optical iodine frequency reference.We compare the optical frequency to a chip-scale atomic clock (CSAC) via a self-referenced frequency comb on the ground and in space. This paper is organized as follows. Section II describes the optical iodine frequency reference and its autonomous operation, as well as the optical frequency comb used to verify the frequency instability of the iodine reference aboard the sounding rocket. Section III presents results on the characterization of the frequency instability of the iodine frequency reference obtained on the ground and from the operation in space. Finally, in Sec. IV, we summarize the results and give a conclusion

An Optical Absolute Frequency Reference For A Sounding Rocket Mission Based On Iodine

We present a compact absolute optical frequency reference based on hyperfine transitions in molecular iodine for application on a sounding rocket mission. It is based on a micro-integrated extended cavity diode laser at 1064 nm with integrated optical amplifier, fiber pigtailed second harmonic generation wave-guide modules, and a quasi-monolithic spectroscopy setup with operating electronics. This frequency reference is scheduled for launch end of 2017 aboard the TEXUS 54 sounding rocket as an important qualification step towards space application of iodine frequency references and related technologies. We aim for a fractional frequency instability of better than 3 × 10−14. The payload will operate autonomously and its optical frequency will be compared to an optical frequency comb during its space flight

Enthalpy Changes during Photosynthetic Water Oxidation Tracked by Time-Resolved Calorimetry Using a Photothermal Beam Deflection Technique☆☆☆

The energetics of the individual reaction steps in the catalytic cycle of photosynthetic water oxidation at the Mn4Ca complex of photosystem II (PSII) are of prime interest. We studied the electron transfer reactions in oxygen-evolving PSII membrane particles from spinach by a photothermal beam deflection technique, allowing for time-resolved calorimetry in the micro- to millisecond domain. For an ideal quantum yield of 100%, the enthalpy change, ΔH, coupled to the formation of the radical pair YZ⋅+QA− (where YZ is Tyr-161 of the D1 subunit of PSII) is estimated as −820 ± 250 meV. For a lower quantum yield of 70%, the enthalpy change is estimated to be −400 ± 250 meV. The observed nonthermal signal possibly is due to a contraction of the PSII protein volume (apparent ΔV of about −13 Å3). For the first time, the enthalpy change of the O2-evolving transition of the S-state cycle was monitored directly. Surprisingly, the reaction is only slightly exergonic. A value of ΔH(S3 ⇒ S0) of −210 meV is estimated, but also an enthalpy change of zero is within the error range. A prominent nonthermal photothermal beam deflection signal (apparent ΔV of about +42 Å3) may reflect O2 and proton release from the manganese complex, but also reorganization of the protein matrix