Mode-locked solid-state laser apparatus

A mode-locked solid-state laser apparatus, comprising:

• an output mirror that forms a first end of a resonator;
• a saturable absorption mirror that forms a second end of the resonator;
• a solid-state laser medium disposed at a position inside of the resonator where the distance from the saturable absorption mirror is not greater than twice a Rayleigh length;
• an excitation optical system that inputs excitation light from outside into the resonator;
• a negative group velocity dispersion element, disposed inside of the resonator, that causes group velocity dispersion of the entire resonator to be not greater than 0 when light makes one round trip in the resonator;
• a dichroic mirror, disposed inside of the resonator, that reflects the excitation light inputted from outside into the resonator by the excitation optical system toward the solid-state laser medium and transmits oscillation light;
• wherein the negative group velocity dispersion element is either one of a prism pair, a diffraction grating pair, and a negative dispersion mirror pair or a combination of two or more of them;
• and
• the negative group velocity dispersion element is physically separated from the output mirror of the resonator,
• the solid state laser medium and saturable absorption mirror are disposed in close proximity to each other at a distance not greater than twice a Rayleigh length, wherein said Ra¥leigh length is obtained on the basis of beam waist diameter at the saturable absorption the saturable absorption mirror has an absorption modulation depth OR not less than 0.4%;
• and
• the absolute value |D| of a total intracavity linear dispersion amount D when light having a predetermined wavelength makes one round trip in the resonator, which is represented by the following relational expression, is set within a range of minimum value 0 to maximum value which is calculated from pulse bandwidth Δλp, in which ΔG(CW)<ΔR/2 and ΔG(DP)≦ΔR/S are satisfied (where, ΔG(CW is the gain advantage of the CW background with respect to the fundamental soliton pulse, ΔG(DP) is the gain advantage of the double pulse with respect to the fundamental soliton pulse in the resonator, and S is the saturation level of the saturable absorption mirror),
• |D|=((1.76AeffLcΔλp)/(4πn2Is*0.315λ0Ep)
• (where c is the velocity of light, λ0 is the center wavelength, AeffL (=πΩL2) is the oscillation light beam cross section at the laser medium, n2 is the nonlinear refraction index Is is the crystal length of the laser medium, and Ep is the intracavity pulse energy).