Laser arrangement with auxiliary ring

The use of a transparent auxiliary ring having a ring inner diameter dR and a length lR, which auxiliary ring has an inner lateral surface, an outer lateral surface, a first end surface and a second end surface and is suitable for reflecting non-useful light, coupled in at the first end surface, at the inner lateral surface by means of total internal reflection and for coupling out and/or scattering and/or absorbing said light at the second end surface and/or the outer lateral surface,

• for adjusting and/or for operating and/or for protecting a device for coupling laser radiation into an optical fiber, wherein the device comprises a focus lens having an effective aperture D and a focal length f, wherein the focus lens focuses the laser radiation in the direction of the fiber end face into a focus, wherein
• the first end surface is arranged in a first plane situated at a distance s upstream of the focus, and the ring inner diameter dR is less than D·s/f, and
• the inner lateral surface is centered with respect to the optical axis, and
• the length lR of the auxiliary ring is less than the distance s.

A method for coupling laser radiation into an optical fiber, wherein the optical fiber has a coupling-in end having a fiber end face, comprising

• a) providing at least one collimated beam bundle,
• b) focusing the collimated beam bundle into a focus by means of a focus lens,
• c) coupling the focused beam bundle into the optical fiber,
• wherein the focus lens has an effective aperture D, a focal length f, an optical axis and a fiber-side lens surface,
• wherein a transparent auxiliary ring having a ring inner diameter dR and a length lR is provided, wherein the auxiliary ring has an inner lateral surface, an outer lateral surface, a first end surface and a second end surface, wherein the auxiliary ring is arranged in the beam path downstream of the focus lens, and
• the first end surface is arranged in a first plane situated at a distance s upstream of the focus, and
• the ring inner diameter dR is less than D·s/f, and
• the inner lateral surface is centered with respect to the optical axis, and
• the length lR of the auxiliary ring is less than the distance s,
• wherein the auxiliary ring is suitable for reflecting rays, coupled in at the first end surface, at the inner lateral surface by means of total internal reflection and for coupling out and/or scattering and/or absorbing said rays at the second end surface and/or the outer lateral surface.