Laser device, light source, and measurement apparatus
Provided is a laser device in which: a laser medium doped with ytterbium emits light upon absorption of excitation light; the light emitted by the laser medium is amplified to obtain output light; and the output light is outputted in the form of a plurality of pulses. In the laser device, a spatial filter is disposed in the optical path of the light emitted by the laser medium or is disposed in the optical path of the output light outputted from an optical resonator, the spatial filter being configured to filter out a portion of the light or of the output light around the optical axis.
1. A laser device comprising an optical resonator that includes a saturable absorber and a laser medium that is arranged to emit light upon absorption of excitation light, the laser medium being arranged to emit the light upon an input of the excitation light, which is pulsed light, into the optical resonator, the optical resonator being arranged to amplify the light emitted by the laser medium to obtain laser light and output the laser light as output light,
the laser medium being doped with ytterbium (Yb),
a pulse width of the excitation light, a cavity length of the optical resonator, and the saturable absorber being set such that the excitation light is single-pulsed light and that the output light is composed of a plurality of pulses,
the laser device comprising a spatial filter that is disposed in an optical path of the light inside the optical resonator or that is disposed in an optical path of the output light outside the optical resonator, the spatial filter:
having a cylindrical opening portion extending along a light path extending through the spatial filter, the cylindrical opening portion having a length along an optical axis of the light path that is shorter than a Rayleigh length of a beam waist of the light or of the output light, and
being configured to filter out a portion of the light or of the output light around the optical axis so as to bring a transverse oscillation mode close to single mode.
2. The laser device according to claim 1 , wherein the laser medium is a medium obtained by doping yttrium-aluminum-garnet (YAG) with ytterbium (Yb).
3. The laser device according to claim 2 , wherein an output pulse width of the output light is not less than 4 ns.
4. The laser device according to claim 1 , wherein an output pulse width of the output light is not less than 4 ns.
5. The laser device according to claim 1 , wherein the spatial filter includes: an optical system that is configured to cause light to converge; and a diaphragm that is configured to filter out a portion of the light around the optical axis at a beam waist of the light.
6. The laser device according to claim 1 , wherein the saturable absorber is doped with chromium (Cr).
7. The laser device according to claim 6 , wherein the saturable absorber is a saturable absorber obtained by doping yttrium-aluminum-garnet (YAG) with chromium (Cr).
8. The laser device according to claim 7 , wherein the laser medium and the saturable absorber are integral with each other.
9. The laser device according to claim 1 , wherein the laser device is for use as a source of pump light for optical parametric oscillation.
10. A light source comprising: a laser device as set forth in claim 1 ; an optical parametric oscillator that includes a non-linear crystal which is configured to wavelength-convert laser light outputted by the laser device to light with a wavelength longer than that of the laser light; and an optical system that is configured to output the laser light which has been wavelength-converted by the optical parametric oscillator.
11. A measurement apparatus comprising:
a light source as set forth in claim 10 ; and
a light detector that is configured to detect light that has been outputted by the light source and reflected at a to-be-measured object or that is configured to detect light that has been outputted by the light source and passed through the to-be-measured object.