The area of LD pump single Nd: YAG is wided continuously, is widely used in science research, spectrum, optics deposited, coherent communication, color display, laser radar, optics scale, gravitation wave detect, medicine, second-time syntony wave occur, parameter surge and constringent photic field occurring. People have researched many methods to make the laser single mode output for many years, there are already annular cavity, twisted-mode cavity (insert 1/4 wave plate in standing wave cavity), short absorb, double-refraction filter, slice cavity and so on. These project are limited. Can’t insert double frequency components in slice cavity; short absorb require the laser working matter very short, so it’s hard to get high pump absorb efficiency; and about other projects, due to it occur large ullage when inserting components, or they are limited by choosing frequency, so it’s hard to get high output power and high efficiency single mode output.

 Dream Lasers use LD cling method, end pump Nd:YVO4 crystal, use the method of combining multiple cavity and Bruce plate to realize the effectively choosing single longitudinal mode, and realize SLM Green laser’s solid, miniaturization, good stability and high efficiency output.

 Basic principle:
Mirror M and Mirror M2 compose syntony cavity. Another sub-cavity is composed by Mirror M and Mirror M1. The length of total cavity is L2, it’s syntony frequency is:

ν2i
ν2i=qic/(2∑nlLl) (1)
The length of sub-cavity is L1, it’s syntony frequency isν1i
ν1i=qic/(2∑nkLk) (2)
in this formula：L2=∑nlLl，L1=∑nkLk，but nl,Ll,Nk and Lk is the relevant length and refractive
rate of the cavity. Whenν0=ν2i=ν1j，the light which frequency isν0 is the strongest in the cavity. If the frequency is the same as 1064nm’s frequency νL, then the light which frequency is VL will oscillate first, making the number of reversal particle saturated and plus curve dropped, then it will control other longitudinal mode’s surge, making the laser is single longitudinal mode.Bruce plate choosing mode principle:

For the laser that is LD end pump Nd:YVO4—KTP double frequency in cavity, Nd:YVO4 is
anisotropic uniaxial crystal, the light is line polarization which is radiated when LD end pump.
When the line polarization light is incidence the Bruce plate at Bruce angle, and polarization direction is parallel with incident surface, the ullage is zero. For KTP, it’s light axis is parallel with the crystal surface and the angle is 45°with incidence basis frequency light’s polarization direction. When the basis frequency line polarization light through KTP, it’s decomposed o light and e light, out and home discrepancy δ isδ=4πd(no-ne)/λ

in this formula：d is the length of KTP crystal, no and ne is the different refraction rate which is occurred by different longitudinal mode in o light and e light, λ is the wavelength in vacuum which is occurred by different longitudinal mode. Only when δ=mπ, come back the same longitudinal mode of Bruce plate’s light polarization direction and original polarization direction, it’s ullage is zero. For other longitudinal mode, it will have different degree ullage. If let 1064nm light meet δ=mπ, then 1064nm’s light ullage is zero, light strong is the strongest, first surge, making the number of reversal particle saturated and plus curve dropped, then it will control other longitudinal mode’s surge, making the laser is single longitudinal mode.