Abstract: The invention relates to a single-mode laser provided with a folded optical resonator, comprising a laser rod 1, resonator mirrors 3A, 3B deposited by evaporation on a single mirror plate 3, a stop 6 provided with two separate apertures 6A, 6B which are overlapped by the laser rod 1 when they are viewed along it and which are located so that the rays traversing the aperture 6A or 6B towards the resonator mirrors 3A, 3B, respectively, completely impinge only on the high reflecting resonator mirror 3A or on the semitransparent resonator mirror 3B, a foil Q-switch 5 and a reversing prism 4.The device according to the invention is compact, of moderate price and is provided with a dynamically stable optical resonator, it generating single-mode laser pulses with a divergence below 2 mrad, but with an energy about 15 mJ and with a width about 10 nsec.The device according to the invention is intended for use e.g. in ophthalmology or elsewhere where the laser pulses characterized above are required.