Laser apparatus includes a laser the output of which is formed into a collimated beam then focused into a transport fiber at a particular effective numerical aperture. A parallel plate is located in the collimated beam and can be variably inclined with respect to the collimated beam for varying the effective numerical aperture of the radiation focused into the fiber. In one embodiment, a second parallel plate is located in the focused beam, and can be variably inclined with respect to the focused beam for aligning the focused beam with the optical fiber.