DPSS Laser is the short form of  'Diode Pumped Solid State Laser'.

Solid State Laser is not the diode laser. It's the solid state laser pumped from laser crystals such as Nd:YAG, Nd:YVO4, Nd:YFL, Yb:YAG and etc. The regular wavelength for example includes 1064nm, 914nm, 1047nm, and etc. The beam quality is usually in very good status which is quite suitable for industry use. For example, the 50W DPSS module in my EBAY list is widely used in metal marking.

Diode Laser is the beam from laser diode emitters or laser diode bars with wavelength of 632nm, 808nm, 915nm, 980nm. These are diode lasers. Usually the diode laser can not be used directly because of the very bad beam quality. Most of the time, we use diode laser beam to pump the solid state laser crystals to get good quality beam.

So for DPSS, there are 2 important pieces: the laser diode & laser crystal. The easy way to build a DPSS laser is using a diode bar or high diode emitter to pump Nd:YAG. Here are some popular pumping methods:

A. Side pumping Nd:YAG rod

This is a quite easy way to pump the YAG. Just put the Nd:YAG rod between the HR  and  OC laser mirrors. Then pump the YAG rod directly or indirectly from side. Carefully adjust the HR, OC, and YAG rod to let each surface in parallel and in-line with a He-Ne laser.  The resonator length is usually 200-700mm as my experience.

Drive the diode bar to pump the YAG rod with 808nm beam (802-809nm is suitable), and then you will get 1064nm output from the OC.

As my experience, it needs at least 30-50 watts 808nm pumping beam to get 1064nm output. This is the threshold power of the YAG rod.

Side Pumping is usually used for high power industry laser up to 10KW or even more. It is easy to get large output from side pumping structure, however, the beam quality is usually not very good. The thermal lensing will get worse while the pumping power is growing.  For a 50W DPSS module, the beam quality factor M2 is usually 10-20.

Here we introduced the beam quality factor (for Gaussian beam) M2.

M2=πDΘ/λ

π is 3.14

D is the waist diameter of Gaussian beam

Θ is the far field beam divergence (full).

λ is the wavelength.

In theory, M2 is always > 1. The M2 is smaller, the beam quality is better. To improve the M2, the key is to reduce D and Θ. To reduce D, you need to use a smaller YAG rod, or reduce the emitting area. To reduce Θ, you have to enlarge the resonator, cool the YAG rod better and reduce the thermal lensing and etc. For more details, please visit Chapter 2. Hehe.

Back to side pumping. Side pumping is usually used for high power industry applications such as metal marking (bold & deep, but not slim), steel cutting, metal welding, military use and etc.

B. End pumping Nd:YAG crystal

Usually end pumping is better in beam quality than side pumping, but it is quite hard to reach very high power output. For the 10W end pumping, the M2 can reach less than 1.5, with beam diameter less than 1mm and very little divergence.

End pumping ...

I will finish this article in the future 2-3 weeks once I have time.