FIG.  15 and FIG.  16 show semiconductor excitation solid-state laser apparatuses (solid-state laser oscillators) based on the conventional technology respectively.  It should be noted that FIG.  16 is a cross-sectional view of the apparatus taking along the line XVI--XVI shown in FIG.  15.  The semiconductor excitation solid-state laser apparatus comprises a solid-state laser medium 101, a semiconductor laser 103 as a laser excitation source, and an optical guide plate 105 made with a rectangular solid plate for propagating a beam excited in the semiconductor laser 103 to the solid-state laser medium 101. 
An excited beam emitted from the semiconductor laser 103 goes into the optical guide plate 105 with a certain angle of divergence, and reaches the side of the solid-state laser medium 101 being totally reflected on the internal side face of the optical guide plate 105, and is absorbed in the solid-state laser medium 101. 
When a semiconductor laser with a large angle of divergence is used, it is required to make larger a thickness (an area of an excited-beam receiving surface) of the optical guide plate 105 so that all the excited beam emitted from the semiconductor laser 103 goes into inside of the optical guide plate 105, but the optical guide plate 105 in the conventional type of semiconductor excitation solid-state laser apparatus is a rectangular solid plate in its shape, so that an area of the beam outgoing surface of the optical guide plate 105 in the side of the solid-state laser medium 101 becomes also larger according to a larger area of the excited-beam receiving surface of the optical guide plate 105, whereby the excited beam is not absorbed in the solid-state laser medium 101, so that a proportion as a loss due to the excited beam going back along inside the optical guide plate 105 becomes larger. 
To efficiently transmit a beam, it is required to third-dimensionally set positions of a semiconductor laser chip incorporated in the semiconductor laser 103 as well as of the optical guide plate 105 with a precision at a specified level or more.  FIG.  17 shows an influence of a vertical error (displacement of an optical axis) between the semiconductor laser chip and the optical guide plate onto a coupling loss.  The x-axis indicates a proportion of a vertical error to the thickness of the optical guide plate.  The coupling-loss curve shown in FIG.  17 is different depending on a divergence angle of an outgoing beam from the semiconductor laser chip as well as on a material of the optical guide plate.  This example shows the fact that, when the vertical error exceeds 30%, a coupling loss abruptly increases. 
FIG.  18 shows an influence of a gap in the direction of the optical axis between the semiconductor laser chip incorporated in the semiconductor laser and the optical guide plate onto a coupling loss.  The coupling-loss curve in this case is also different depending on a divergence angle of an outgoing beam from the semiconductor laser chip as well as on a material of the optical guide plate 105.  This example shows the fact that, when the gap error exceeds 25%, a coupling loss gradually increases.