Narrow Linewidth Opo Light Source For Precision Spectroscopy

Precision spectroscopy of fundamental bands of molecules in the mid-infrared (MIR) region is of great interest in applications of trace detection and testing fundamental physics, where high-power and narrow-linewidth MIR lasers are needed. By controlling the phase noise of the signal and pump light of a continuous wave optical parametric oscillator (OPO), we established a broadly tunable MIR light source which has an output power of several hundred milliwatts and a linewidth of a few tens kilohertz. The long term frequency drift of the MIR laser was reduced and calibrated utilizing a near-infrared optical frequency comb. The performance of the light source was investigated and the laser system will be used for precision measurement of fundamental vibration of HD

LAMB DIP MEASUREMENTS OF MOLECULES WITH KHZ ACCURACY IN THE MID-INFRARED

Precision spectroscopy of molecules in the mid-infrared region where the fundamental bands are located is of great interest in fundamental physics. In order to achieve a high accuracy, one can measure the spectroscopy in the Lamb-dip zone with sub-Doppler resolution, where further reduction of the laser linewidth and transit-time broadening is perspective. Here we report a new method to reduce the mid-infrared laser linewidth of an optical parametric oscillator (OPO) by locking the pump and idle lights to a frequency comb, resulting in a narrow linewidth and good long-term stability of the signal laser. In this way, we demonstrate that the measured Lamb dip linewidth can be as narrow as tens of kHz and the transition frequency can be determined to an accuracy of a few kHz

A MOLECULAR FOUNTAIN

The resolution of any spectroscopic experiment is limited by the coherent interaction time between the probe radiation and the particle that is being studied. The introduction of cooling techniques for atoms and ions has resulted in a dramatic increase of interaction times and accuracy, it is hoped that molecular cooling techniques will lead to a similar increase. Here we demonstrate the first molecular fountain, a development which permits hitherto unattainably long interrogation times with molecules. In our experiment, beams of ammonia molecules are decelerated, trapped and cooled using inhomogeneous electric fields and subsequently launched. Using a combination of quadrupole lenses and buncher elements, the beam is shaped such that it has a large position spread and a small velocity spread (corresponding to a transverse temperature of less than 10$mu$K and a longitudinal temperature of less than 1$mu$K) while the molecules are in free fall, but strongly focused at the detection region. The molecules are in free fall for up to 266 milliseconds, making it possible, in principle, to perform sub-Hz measurements in molecular systems and paving the way for stringent tests of fundamental physics theories

NARROW LINEWIDTH OPO LIGHT SOURCE FOR PRECISION SPECTROSCOPY

Precision spectroscopy of fundamental bands of molecules in the mid-infrared (MIR) region is of great interest in applications of trace detection and testing fundamental physics, where high-power and narrow-linewidth MIR lasers are needed. By controlling the phase noise of the signal and pump light of a continuous wave optical parametric oscillator (OPO), we established a broadly tunable MIR light source which has an output power of several hundred milliwatts and a linewidth of a few tens kilohertz. The long term frequency drift of the MIR laser was reduced and calibrated utilizing an optical frequency comb. The performance of the light source was investigated and tested by measuring the saturated absorption spectroscopy of a few molecular transitions at 3.3 $\mu$m

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements