Deceleration and Trapping of SrF Molecules

We report on the electrostatic trapping of neutral SrF molecules. The molecules are captured from a cryogenic buffer-gas beam source into the moving traps of a 4.5-m-long traveling-wave Stark decelerator. The SrF molecules in $X^2{\mathrm{\Sigma }}^{+}(v=0,N=1)$ state are brought to rest as the velocity of the moving traps is gradually reduced from $190\mathrm{m}/\mathrm{s}$ to zero. The molecules are held for up to 50 ms in multiple electric traps of the decelerator. The trapped packets have a volume (FWHM) of $1{\mathrm{mm}}^3$ and a velocity spread of $5(1)\mathrm{m}/\mathrm{s}$, which corresponds to a temperature of 60(20) mK. Our result demonstrates a factor 3 increase in the molecular mass that has been Stark decelerated and trapped. Heavy molecules ($\mathrm{mass}>100\mathrm{amu}$) offer a highly increased sensitivity to probe physics beyond the standard model. This work significantly extends the species of neutral molecules of which slow beams can be created for collision studies, precision measurement, and trapping experiments.

Figure 1

(a) Experimental setup: The SrF molecules are produced in a cryogenic buffer-gas source. On exiting from the cell, molecules enter the 4.5-m-long TWSD that is mounted 36.9 cm behind the source exit. The molecules travel through the decelerator in the guided or the deceleration mode. They are then detected at a distance of 1 cm from the last ring electrode of the TWSD. (b) The typical absorption signal of the molecular beam measured at a distance of 5 mm from the cell exit. (c) The experimental time-of-flight profile with a bin size of $200\mu \mathrm{s}$, shows the guiding of the molecular beam of SrF with an average velocity of $190\mathrm{m}/\mathrm{s}$ at 5.0 kV. Inset: an enlargement of the guided peak with a bin size of $5\mu \mathrm{s}$, which shows the individual electric field traps filled by the molecules inside the TWSD.

Figure 2

Time-of-flight LIF signals depicting the deceleration of SrF molecules from $190\mathrm{m}/\mathrm{s}$ to different final velocities until $10\mathrm{m}/\mathrm{s}$ at a voltage amplitude applied to the decelerator of 5 kV with a bin size of $200\mu \mathrm{s}$. A vertical offset has been added to different plots for clarity.

Figure 3

Enlarged view of the time-of-flight histograms around the arrival time of the decelerated peaks with a bin size of $5\mu \mathrm{s}$, for a few selected final velocities 170, 130, 90, 50, $30\mathrm{m}/\mathrm{s}$. The peaks labeled (*) correspond to the synchronous molecules, which represent the first packet of molecules that is detected after the electric fields of the decelerator are switched off.

Figure 4

Time-of-flight histograms with a bin size of $400\mu \mathrm{s}$ demonstrating the trapping of SrF molecules for different trapping times $\mathrm{\Delta }t$. The undecelerated molecules are only shown for the case of $\mathrm{\Delta }t=0$. A vertical offset has been added to the plots for clarity. The inset shows an enlargement of the trapping peak for the case of $\mathrm{\Delta }t=50\mathrm{ms}$.