Patent ID: 7573921

Claim:
A laser light source comprising: a first laser for generating a laser beam of a wavelength λ 1 ; a second laser for generating a laser beam of a wavelength λ 2 ; and a nonlinear optical crystal that uses the laser beam of the wavelength λ 1 and the laser beam of the wavelength λ 2 as inputs and outputs a coherent beam having a wavelength λ 3 of a difference frequency that satisfies a relationship of 1/λ 1 −1/λ 2 =1/λ 3 , and wherein: the wavelength λ 1 is selected in the range of 0.9-1.0 μm, the nonlinear optical crystal is LiNbO 3 having a periodically poled structure of a single period and satisfies a relation as follows: sin 2 ⁢ ⁢ ( Δ ⁢ ⁢ kl 2 ) ( Δ ⁢ ⁢ kl 2 ) 2 ≥ 0.5 ⁢ ⁢ where Δ ⁢ ⁢ k = k 3 - k 1 + k 2 + 2 ⁢ ⁢ π Λ , k i = 2 ⁢ ⁢ π λ i ⁢ ⁢ n i , and l is a length of the nonlinear optical crystal, refractive indices of the wavelengths λ 1 , λ 2 , and λ 3 are represented by n 1 , n 2 , n 3 , respectively, and Λ is the single period, and the wavelength λ 3 of a difference frequency varies between 3.1 μm and 2.0 μm when the wavelength λ 2 varies between 1.3 μm and 1.8 μm.