A laser absorption spectrometer for making measurements of absorption spectra which includes a wavelength sensor that can measure the average wavelength of pulses from a laser on a pulse-by-pulse basis and that can measure the internal wavelength variation of laser pulses. In the semiconductor device, the insulating substrate is composed of cBN or diamond. 1 wt % is provided that has increased wear resistance and increased fracture toughness over conventional steel rail. The spindle motor may be capable of turning the spindle at a set of different speeds during the drilling operation. The main controller decreases the power of the pump light supplied to the amplification section, on the occasion of ending the output of the pulsed laser light, and thereafter makes the pulse modulator end the output of the seed light from the seed light source.