A laser system has an output/input coupler unit (49) with a circulator (37). An output of the circulator (37) is operationally connected to a detector unit (43). The input/output (EA37) of the circulator is operationally connected to a transmitter and a receiver optics 41. Laser light is input to the circulator (E37). The input (E37), output (A37) and output/input (EA37) of the circulator are optical fibers. The pulsed diode (3) is not temperature stabilized. To reduce amplified spontaneous emission (ASE) generated in the optical fiber amplifier (9), a narrow band-pass filter unit (29) is used. Filter unit (29) has a central wavelength with a temperature dependence which is matched to the temperature dependent wavelength shift of the pulsed diode (3).