Obviously, the prerequisite for laser generation is that a strong beam rich in ultraviolet and green light shines into the laser rod, so that the ion inversion density reaches the threshold. A widely used method is to use pulsed xenon lamp to strengthen the light source. The structure is very simple, as long as the light from the xenon lamp is projected onto the ruby stick. Flash has several important parameters. In fact, we only care about two, arc length 1800v, and the energy of lamp explosion under electrolytic capacitor. Generally, in order to adapt to industrial use, the nominal working voltage of the data table is above1500 V, and only when this energy storage voltage is met can the nominal light energy density and pulse width be achieved (the main peak is below 0.5ms, which meets the needs of drilling).

Mainstream flash has the following two types:

1, the earliest structure is ring flash.

The world's first laser used a multi-ring flash. The efficiency is not as high as linear flash, but the energy tolerance is much greater. This kind of flashlight is generally difficult to buy, the tube length is too long to trigger, the pulse shaping network is difficult to make, and the capacitor storage voltage is high, but it is suitable for being a flashlight that can withstand very large energy. It is very difficult to model this kind of flash memory, and the data sheets are very different, so there is no general summary rule. Generally, the working endurance exceeds 2KJ.

2. But later, a linear flash appeared.

At present, more than 80% of industrial solid-state lasers adopt this xenon lamp structure. High pumping efficiency, convenient water cooling, simple manufacturing process and easy triggering are the reasons why most industrial lasers adopt this structure. These flashlights are pulsed xenon lamps. A typical value is that a xenon lamp with an arc length of 10cm and a diameter of 8mm can easily accommodate 2200J energy under 400V energy storage. From the simple circular cavity used in the ring flash lamp at first, to the elliptical reflection cavity (double focus), double elliptical cavity (triple focus) and diffuse reflection cavity that appeared later.

In fact, the efficiency of these modern and latest reflecting cavities is between 80% and 95%, and it is acceptable to exceed 60% under amateur conditions. You know, wrapping a flash and a laser bar with white paper can reach 60%.

1, elliptical mirror reflector (suitable for water cooling, but difficult to process. Only one xenon lamp can be installed, and the spot energy distribution of the output light is not particularly uniform)

The bracket can be made of processing material and covered with mirror mask, such as polished aluminum foil paper or silver-plated copper skin. Or directly flatten it with a section of aluminum tube with a slightly diffused polishing belt point inside.

It can also be directly processed by machine tools.

The advantage of this kind of cavity is that it can realize high machining accuracy and dense pulse. Generally, only laser rapid finishing equipment adopts this scheme.

A variant of elliptical cavity-double elliptical reflector cavity can hold two lamps, and at the same time, it is convenient for water cooling, achieving good quasi-continuous output effect of large energy, as many laser weapons did in the 1980s. Have the ability to deal with this form can be considered. The picture shows the cross-sectional structure and optical density of rod-shaped section simulated by ZEMAX software in a paper. The spot quality is not very good, but it can reach great energy. For example, a Nd glass rod with a diameter of 40mm and a length of 90cm can achieve a pulse output of 2000J with this structure, which requires a capacitor of 100kJ for energy storage. Each flash lamp shares 50KJ of energy, which is easy to reduce the volume and facilitate water cooling.

2. Wrap the diffuse reflection cavity tightly

The efficiency does not have to be much different from that of the elliptical cavity. If it is water-cooled, it can be made of ceramics and rubber without polishing, which greatly reduces the technical difficulty and becomes the method used in more than 90% industrial applications. A relatively simple method is to wrap it tightly with aluminum foil paper, which can easily achieve more than 90% efficiency. If copper-clad silver foil is used, the efficiency can be further improved, and the structure is as simple as that.

The simulation results in this paper are very good and the spot quality is satisfactory.

Considering that some devices require high efficiency of the reflection cavity, this is the relationship between reflectivity and wavelength of two commonly used coating reflective materials (gold and silver), which have excellent corrosion resistance and optical properties. Please refer to the table.

Gold begins to reflect from above 500 nm, which makes it not suitable for ruby laser (mostly absorbing ultraviolet and green light), but suitable for YAG laser (ultraviolet will inhibit the efficiency of laser). Silver has a wider emission wavelength range and is more suitable for ruby laser. Although the performance in the infrared range is not as good as that of gold, the difference is not too big.