Patent ID: 7894131

Claim:
A laser microscope comprising: a laser light source configured to emit ultrashort-pulsed laser light; an objective lens adapted to face a specimen; a pulse expander which comprises an optical system producing negative dispersion, and which is configured to expand the ultrashort-pulsed laser light emitted from the laser light source and adjust an amount of negative dispersion in order to minimize a pulse width of the ultrashort-pulsed laser light exiting the objective lens; a large-diameter single-mode fiber configured to transmit the ultrashort-pulsed laser light expanded by the pulse expander; a pulse compressor which comprises one of: (i) an isotropic, high-refractive-index, positive-dispersion material, and (ii) an anisotropic, high-refractive-index, positive-dispersion material, and which is configured to compress the ultrashort-pulsed laser light transmitted by the single-mode fiber; and a microscope main body configured to irradiate the specimen with the ultrashort-pulsed laser light compressed by passing through the pulse compressor; wherein the single-mode fiber has a core diameter that is at least equal to a minimum effective core diameter set according to the following equations: D min =2×√( A eff /π) (1) A eff =2 π/λ×n 2 ×P o — max ×L/a (2) P o — max 2×√( ln 2/π)× P ave /(Δ t in ×ν) (3) Δ t in ≈Δt out ×√{1+7.68×[( GDD f +GDD c )/(Δ t out 2 )] 2 } (4) where D min is the minimum effective core diameter of the single-mode fiber; A eff is an effective cross-sectional core area; λ is a wavelength; n 2 is a nonlinear refractive index of the single-mode fiber; a is a constant; L is a length of the single-mode fiber; P o — max is a maximum incident peak intensity on the fiber for which it is possible to transmit a pulse of Δt out or less; P ave is an average output power at an exit end of the fiber; ν is a repetition frequency; Δt in is an incident pulse width at the fiber; Δt out is an exit pulse width of the objective lens; GDD f is a group delay dispersion of the fiber; GDD c is a group delay dispersion of the pulse compressor and the microscope main body; Δt out is set to range from about 1 to 3 times a pulse width of the laser light source; P o — max corresponding to the set Δt out is determined by an experimental system constructed for introducing the ultrashort-pulsed laser light into the fiber; and a is determined by the following equations: γ=(2π/λ)·( n 2 /A eff ) (5) L n1 =1/(γ· P o — max ) (6) a=L/L n1 =L·γP o — max (7) where γ is a nonlinear constant; and L n1 is a nonlinear length.