Is there any way to change the frequency of the laser's output light wave?

Your question is very general. The wavelength of a laser, as a linear process, is determined by the gain spectrum range and the cavity membrane of the resonant cavity **** the same. No matter how you change the length of the resonant cavity, the laser wavelength will only be within the gain spectrum of its gain medium. In practice you have to think a lot about it, because at the edge of the gain spectrum, the optical gain does not necessarily exceed the loss, and the quality of such a laser signal is poor. Nonlinear lasers have various methods of wavelength tuning: for example, supercontinuum lasers, which are realized by supercontinuum (supercontinueous) of photonic crystal fibers, or there are simple and four-wave mixing (degenerated four wave mixing), Raman lasers (raman laser), and so on. Commercial lasers are most commonly used for frequency modulation by optical parametric oscillation (OPO). This technology is very mature, that is, in the crystal to ensure that the photon momentum, energy conservation, to produce signal and idle two beams of light (signal light and idle frequency light). Through the computer to adjust the angle of incidence, continuously adjust the output light frequency. The answer downstairs is ridiculous, basic high school level. It is very wrong. First of all, adding voltage is likely to increase the pump power, the general pump power of the laser is high, the number of photons of the output laser increases, indeed, will affect the refractive index of the gain medium, this is called chirp, is chirp, a very disliked in the optical communication inside the nonlinear. Chirp changes the laser wavelength. But I have not seen the use of chirp modulation of wavelength. That optical frequency demodulator is even funnier. Optical frequency of 100T Hz, the current coherent modulation of mankind to hold up to G Hz, that is, high-frequency microwave, simply can not reach the optical frequency. The response of the optical frequency that is the idea of taking the Nobel Prize, a fool's errand.