In recent years, a laser display apparatus using laser light sources of three colors, i.e., red, green, and blue (hereinafter referred to as “RGB lasers”) has been proposed. Since the laser display apparatus employing the RGB lasers is capable of realizing monochromacy and a broad color representation range of laser, a color display of highly vivid is enabled.
To realize a large-screen display apparatus using RGB lasers, a laser light source of several watts is needed. As means for realizing such laser light source, a high output power Ar laser or Kr laser has been conventionally used. However, since energy conversion efficiencies of these gas lasers are quite low as about 0.1%, a large-scale apparatus construction including a cooling device is needed.
In order to solve this problem, light generation of short wavelength light using a solid laser has been examined.
For example, by carrying out wavelength conversion of light of 1.064 μm emitted from a solid laser such as YAG into a second harmonic by a wavelength conversion element, generation of high power green light is realized. Recently, generation of high output power green light using a Yb-doped fiber laser has been reported, and further, non-patent Document 1 reports that generation of green light of 60 W can be realized by, using a LBO crystal (nonlinear optical crystal: LiB3O5) as a wavelength conversion element, carrying out wavelength conversion of light of fundamental wave that is entered thereto by the wavelength conversion element.
Further, there have been proposed methods of using green light or blue light which is directly generated from a solid laser as a light source. For example, patent Document 1 suggests and discloses a method of generating red light and green light by exciting a laser medium doped with trivalent praseodymium ion (Pr3) with a GaN system semiconductor laser, and applying the lights in a laser display apparatus.    Non-patent Document 1: Optics Letters vol. 30, No. 1, pp. 67-69 (2005)    Patent Document 1: Japanese Published Patent No. 2001-264662