Semiconductor pumped 532nm green laser has the advantages of short wavelength, high photon energy, small size, high efficiency, high reliability, long service life, long transmission distance in water, and human eye sensitivity. In recent years, it has played an extremely important role in spectrum technology, laser medicine, information storage, color printing, underwater communication and other fields, thus becoming a research hotspot in various countries. Semiconductor pumped 532nm green laser is suitable for nonlinear optical experiments in modern physics teaching in universities. In this experiment, Nd 3+:YVO 4 laser pumped by 808nm semiconductor laser is taken as the research object. The frequency doubling crystal KTP is inserted into the laser cavity to generate 532nm frequency doubling light. The frequency doubling phenomenon, frequency doubling efficiency and phase matching angle were observed.

First, the experimental purpose

1, master the basic method of light path adjustment, observe transverse mode, and measure the relationship between output infrared light and pump energy, oblique efficiency and threshold;

2. Measure the relationship between injection current and power output of semiconductor laser, and understand laser principle and frequency doubling laser technology.

Second, the experimental principle

The interaction between light and matter can be attributed to the interaction between light and atoms. Einstein proposed from the quantum theory of the interaction between radiation and atoms that there are three interaction processes under equilibrium conditions, namely stimulated absorption, stimulated radiation and spontaneous radiation.

Suppose that the ground state energy of an atom is E 1 and the first excited state energy is E 2, as shown in figure 1. If the atom begins to be in the ground state, the energy level state of the atom will remain unchanged when there is no external photon incident. If a photon with energy of 2 12 1hv E E =- is incident, the atom will absorb this photon and jump to the first excited state. The transition of atoms must conform to the transition selection rule, that is, the energy of incident photons is 2 1hv, and the energy level of atoms before absorption is 2 1E-E (for simplicity, spontaneous emission is assumed to be monochromatic here).

Excited States have a short lifetime, and will spontaneously return to the ground state and emit photons without external influence. Spontaneous emission has nothing to do with external effects. Because the radiation of atoms is spontaneous and independent, the emission direction and initial phase of photons emitted by different atoms are random and different, as shown in Figure 2.

If a photon with energy of 2 12 1hv E E =- is incident, the atom will generate a new photon under the excitation of this photon, which will cause stimulated radiation. As shown in Figure 3, the frequency, emission direction, polarization state and initial phase of photons emitted by stimulated radiation are exactly the same as those of foreign photons. Laser is produced by stimulated radiation process.