Diffraction of a CW atom laser in the Raman-Nath regime. (arXiv:1802.01524v1 [physics.atom-ph])

Atom interferometry is the most successful technique for precision metrology.
However, current interferometers using ultracold atoms allows one to probe the
interference pattern only momentarily and has finite duty cycle, resulting in
an aliasing effect and a low-bandwidth measurement -- also known as Dick
effect. Interferometry with a continuous-wave atom laser shows promise in
overcoming these limitations due a continuous monitoring of the interference
pattern. In this work, we demonstrate a key step towards such an interferometry
by demonstrating a diffraction of an atom laser' in the Raman-Nath regime. We
outcouple a continuous beam of coherent atoms from a reservoir of $^{87}$Rb
Bose-Einstein condensate (BEC) upto 400 ms. The atom laser' interacts with a
grating formed by a standing wave of a far detuned laser light. The atom laser
diffracts into several orders going up to 9$^{th}$ order or up to momenta of
$\pm 18\ \hbar k$. We have characterized the diffraction of atom laser for
different conditions and the results match with numerical simulations. Such
atom laser will allow for construction of an atom-interferometer to probe
physics phenomenon continuously up to a time of the order of few hundred
millisecond.