We propose a method for measuring velocities of atoms or molecules in a gas phase based on time-resolved laser experiments. Two intensity gratings of electromagnetic field with variable time delay tau are created by interfering of four laser pulses.
Using first-order perturbation theory, we show that such arrangement can be used for measuring particle velocities, which have an optical transition to a long-living excited state. It is shown that the optical Ramsey oscillations obtain a characteristic modulation that reflects the distribution of velocities.