The mid - infrared laser (2 ~ 5μm) covers many atmospheric transmission windows and many molecular chemical bond absorption peak "fingerprint" regions, which have important application prospects in space optical communication, IR Laser environmental monitoring, medical, military and other fields. There are many techniques for generating mid-infrared laser, which is based on direct-pumped rare earth doped crystal in the infrared laser technology, with a simple structure, continuous output, high beam quality advantages. Directly pumped erbium ion (Er3 +) doped laser crystal is one of the most important techniques to realize infrared laser in 3μm band. In order to solve the problem that the lifetime of the lower energy level (4I13 / 2) of the 3μm laser output channel of the Er ion is much higher than that of the upper energy level (4I11 / 2), the laser ion self- Miscellaneous concentrations are often higher than 30 at%, IR Laser or even 50 at%. However, the high concentration of doping can lead to a significant decrease in the thermal conductivity of the laser crystal, and the enhancement of the excitation level on the laser level (4I11 / 2), resulting in a limited output power and a low laser efficiency in the 3 μm band.
Laser beam compression lens is mainly used for compression of the laser beam divergence angle, observed in the general distance in order to be able to observe the target at different distances, usually using zoom lens, that is close to the beam divergence angle larger, so lighting The light intensity is weakened, IR Laser the imaging part will not be saturated because of the large light intensity, IR Laser long distance so that the beam divergence angle becomes smaller, so that the illumination range is small, light intensity becomes stronger, the imaging part will not because of long-distance attenuation, Great observation distance.
The purpose of the spot shape is mainly to the semiconductor laser spot into a circular or square. We know that the semiconductor laser output spot is oval, horizontal and vertical divergence angle is generally θ‖ × θ⊥ = 8 º × 40 º. Can not be used for direct lighting observation, IR Laser and therefore need to be rounded or square. For the usual finishing rectification for display with a monitor.
CCD light-sensitive surface for the rectangular, and its length to width ratio of 3: 4, so that if we will laser spot shaping the proportion of the line, then just match each other, IR Laser resulting in visual effects are very good. If the angle of view in one of the directions is exactly the horizontal divergence angle (eg 8º) of the laser.
The LD beam is an elliptical Gaussian beam, and the vertical divergence angle of the beam is larger, and its transverse field is somewhat elongated due to the existence of the high order mode. LD beam if the direct use is not get a good lighting effect, and must be its full circle and spot homogenization. The whole process of LD beam can be done by using elliptical microlens or binary optical element.IR Laser We propose the idea of using the optical fiber to make the whole circle and spot uniformity of the LD beam. This method has the advantages of simple structure, few optical components and high coupling efficiency , Suitable for the production of small size, high power lighting source. The fiber used for beam finishing is a step index type multimode single fiber or fiber bundle.