A class of erbium-doped silicate crystals have a general chemical formula of (Er.sub.xYb.sub.yCe.sub.zA.sub.(1-x-y-z)).sub.3RM.sub.3Si.sub.2O.sub.14, in which the range of x is 0.002 to 0.02, y is 0.005 to 0.1, and z is 0 to 0.15; A is one, two or three elements selected from Ca, Sr, or Ba; R is one or two elements selected from Nb or Ta; M is one or two elements selected from Al or Ga. Using one of such crystals as a gain medium and a diode laser at 940 nm or 980 nm as a pumping source, a 1.5 μm continuous-wave solid-state laser with high output power and high efficiency, as well as a pulse solid-state laser with high energy and narrow width can be obtained.

A class of erbium-doped silicate crystals have a general chemical formula of (Er.sub.xYb.sub.yCe.sub.zA.sub.(1-x-y-z)).sub.3RM.sub.3Si.sub.2O.sub.14, in which the range of x is 0.002 to 0.02, y is 0.005 to 0.1, and z is 0 to 0.15; A is one, two or three elements selected from Ca, Sr, or Ba; R is one or two elements selected from Nb or Ta; M is one or two elements selected from Al or Ga. Using one of such crystals as a gain medium and a diode laser at 940 nm or 980 nm as a pumping source, a 1.5 m continuous-wave solid-state laser with high output power and high efficiency, as well as a pulse solid-state laser with high energy and narrow width can be obtained.

According to one embodiment, an optical device includes a first mirror, a second mirror, and a first member. The first mirror has a first planar surface. The second mirror is spaced from the first mirror in a first direction crossing the first planar surface. The second mirror has a concave surface including a first region and a second region around the first region. First distance between the first region and the first planar surface in the first direction is longer than second distance between the second region and the first planar surface in the first direction. The first distance is half or less of curvature radius of the concave surface. The first member is light transmissive and solid. The first member includes a first portion provided between the first mirror and the second mirror. The first portion is in contact with the first planar surface and the concave surface.

According to one embodiment, an optical device includes a first mirror, a second mirror, and a first member. The first mirror has a first planar surface. The second mirror is spaced from the first mirror in a first direction crossing the first planar surface. The second mirror has a concave surface including a first region and a second region around the first region. First distance between the first region and the first planar surface in the first direction is longer than second distance between the second region and the first planar surface in the first direction. The first distance is half or less of curvature radius of the concave surface. The first member is light transmissive and solid. The first member includes a first portion provided between the first mirror and the second mirror. The first portion is in contact with the first planar surface and the concave surface.

According to one embodiment, an optical device includes a first mirror, a second mirror, and a first member. The first mirror has a first planar surface. The second mirror is spaced from the first mirror in a first direction crossing the first planar surface. The second mirror has a concave surface including a first region and a second region around the first region. First distance between the first region and the first planar surface in the first direction is longer than second distance between the second region and the first planar surface in the first direction. The first distance is half or less of curvature radius of the concave surface. The first member is light transmissive and solid. The first member includes a first portion provided between the first mirror and the second mirror. The first portion is in contact with the first planar surface and the concave surface.

A cascaded slow light amplifier and a system comprising such amplifier is described. The amplifier includes a unit wherein each unit comprising of at least one host crystal doped with ions and optically prepared to provide at least one amplification