Abstract: Laser apparatus (1) comprising a reference source (2), a reference fiber (3), and at least one laser diode (4), wherein the reference fiber (3) comprises a core (5) having a refractive index n1 and a first cladding (6) having a refractive index n2, the first cladding (6) is surrounded by a second cladding (7) having a refractive index n3, the refractive index n1 is greater than the refractive index n2, the refractive index n2 is greater than the refractive index n3, the laser diode (4) emits laser radiation (8) that is guided through the first cladding (6) of the reference fiber (3), the reference source (2) emits reference radiation (9) that has a predetermined wavelength ?R (10), the reference radiation (9) is guided through the core (5) of the reference fiber (3) to the laser diode (4), and the reference radiation (9) that is guided through the core (5) of the reference fiber (3) to the laser diode (4) has a power (11) at the predetermined wavelength ?R (10), which power is greater than an injection lockin