CSIST Has Made Progress in the Research of High Efficiency Radiation Resistance Mid Infrared Laser Crystal

2.7~3μm mid infrared laser has important potential application in spectrum analysis, gas detection, laser medicine as well as optical parametric oscillator pumped laser and other areas. Recently, funded by the National Natural Science Fund, a research group lead by SunDun Lu, a researcher from the laser center of Anhui Institute of Optics and Fine Mechanics, Hefei Institute of material science has made a series progress in the research of high efficiency radiation resistance 2.7~3μm mid infrared laser crystal; and has published its research results in Optics Letters,Optics Express.

As for the research of radiation resistance function of laser crystal, researchers has made comparative study about the features of absorption, fluorescence spectrum, level lifetime, laser characteristics and others of Er:GYSGG、Yb,Er,Ho:GYSGG crystal before and after irradiated by 100 Mrad γ ray; results shows that this new type crystal has excellent radiation resistance (Optics Letters, 2013, 38:1218-1220).

 

As for the improvement of mid infrared crystal laser efficiency and high repetitive frequency laser characteristics, researchers mixed in retreat activated ions such as Pr3+, Ho3+ and sensitized ions such as Yb3+, Cr3+; so as to study their impact on Er:GYSGG crystal’s absorption, fluorescence spectrum, level lifetime, laser characteristics and other functions. Results showed that after the mix of retreat activated ions, the laser lower level lifetime of the crystal was reduced, laser efficiency and high repetitive frequency laser characteristics were improved, which laid the foundation for the practical application of the crystal.

 

Furthermore, the research group has been studying crystal thermal bonding technology and the relevant functions. As for GYSGG/Er,Pr:GYSGG thermal bonding composite laser crystal, temperature of the crystal end was lowered, thermal lensing effect was improved, the laser characteristic was obviously increased, pure GYSGG crystal if used as end cap could have the effect of heat sink cooling, and that could realize high performance LD end pumped solid laser (Optics Express, 2014,22:23795-23800).

 

Related work is funded by General Project as well as Training Program of the Major Research Plan of the National Natural Science Foundation of China.

                                          

Chart 1. Laser output power curve of Yb,Er,Ho:GYSGG before and after irradiated by 100 Mrad γ ray

Chart 2. Laser Characteristic curve of Cr,Er,Pr:GYSGG at repeat frequency rate 1~60Hz

                                         

Chart 3. Upper and lower level fluorescence decay curve of Er,Pr:GYSGG

Chart 4. Temperature distribution of end pumped Er,Pr:GYSGGG and GYSGG/Er,Pr:GYSGG

Chart 5. Laser output power characteristics of end pumped Er,Pr:GYSGG and GYSGG/Er,Pr:GYSGG

Laser Drilling Applications in the PCB Industry

Two kinds of laser technique can be used in laser drilling of PCB. CO2 laser wavelength is within far ultrared-ray waveband and ultraviolet laser wavelength is within UV band. CO2 laser is widely used in micro-vias production of printed circuit board, requiring micro-vias' diameter greater than 100μm (Raman, 2001) . It has high productivity in large-size hole manufacturing since it needs very short time to finish punching by CO2 laser. UV laser technique is widely applied in micro-vias production, with diameter less than 100μm even 50μm. It has very high output when produce holes with diameter less than 80μm. Therefore, more and more manufacturers have brought in double-ended laser hole-drilling system in order to meet the increasing demand of micro-vias production.

laser drilling

Below are the three main types of double-ended laser hole-drilling system in current market:
1) double-ended UV drilling system;
2) double-ended CO2 laser drilling system;
3) mixed laser drilling system (with both CO2 and UV) .

Each type has its merit and demerit. Laser drilling system includes double-ended single wavelength system and double-ended dual-wavelength system. Two parts influence the drilling quality:
1) laser power / pulse energy;
2) beam positioning system.

Laser pulse energy and transmission efficiency of beam decide the drilling time, which means the period of time needed to drill a micro-via by laser drilling machine. Beam positioning system decides the speed of movement between two holes. The speed of laser drilling machine is determined by all the factors together. Double-ended UV drilling system is ideally suited to drilling less than 90μm in integrated circuit, with high aspect ratio.

Double-ended CO2 laser drilling system makes use of Q-switch RF-excited CO2 laser. It's principle advantages include high repetition rate (which reaches to 100kHz), short drilling time and wide interface.

In the HDI manufacturing process, mixed laser drilling system is the most popular system composed of UV laser head and CO2 laser head. The comprehensive application of mixed laser drilling methods allows both copper and dielectric medium drilling occur at the same time. Ultraviolet radiation drill the copper to form a particular size and shape, and CO2 laser drill the uncovered dielectric adjacently. The drilling process is to drill a 2inX2in area, which is called domain.

co2 laser

CO2 laser can remove dielectric effectively, even the non-uniform glass-reinforced dielectric. However, it is unable to drill hole less than 75μm and remove copper, with an exception of pre-treated thin copper foil (lustino, 2002) less than 5μm. UV laser can drill very small holes and erase every ordinary copper (3-36μm, 1oz, even electro copper foil). It can also erase dielectric material by itself but it is quite slow. And the result is not good on non-uniform materials like glass-reinforced FR-4. It is because that only when the energy density is improved to some extent, the glass can be successfully removed but bonding pad will be destroyed in the meantime. Since mixed laser drilling system contains both CO2 and UV laser, it can achieve the best result in the two fields, with UV laser in copper foil and small hole and with CO2 laser in fast drilling on dielectric.

At present, the distance between the two heads is fixed in most double-ended laser hole-drilling system, with stepping-repeat beam positioning technology. Stepping-repeat laser remote controller has large regulating range, reaching to 50X50 μm. Its disadvantage is that the laser remote controller has to move in the fixed area, and the separation distance between the two heads is fixed as well. Typical separation distance between the two heads is about 150μm. It is impossible to get the optimum allocation operation like programmable head when it comes to different panel sizes.

Nowadays, there are various specification of performance for double-ended laser hole-drilling system, which can apply to small printed circuit board manufacture as well as mass production.

laser hole-drilling

Ceramic aluminum oxide is used in printed circuit board manufacture for its high dielectric constant. But it is frangible and the mechanical pressure in drilling need to reduce to the minimum, which is an advantage for laser drilling. Rangel had proved in 1997 that Q-switch Nd - YAG laser drilling can be applied in aluminum oxide baseboard and aluminum oxide baseboard covered with gold and anchor. Laser with short pulse, low energy and high-peak power can protect sample from mechanical pressure and make high quality hole less than 100μm.

Interpretation of the Amazing Laser Technology : Laser Crystal

Laser crystal can transfer power from the outside world into crystal material with high parallelism and monochromatic laser in space and time through optical resonator. It’s the operation material of crystal laser. Laser crystal consists of luminescence center and host crystal. Most luminescence center of laser crystal is made up of active ion. While active ion partly replaces the positive ion of the host crystal to form doped laser crystal; while active ion becomes part of the host crystal, then it will become self-activated laser crystal.



Active ions used in laser crystal are mainly transition metal ions and trivalent rare-earth ions. The optical electron of transition metal ion is the 3d electron of the outer shell; this optical electron can be directly affected by the surrounding crystal field, its spectral characteristic differs in different structure type crystals. The 4f electron of the trivalent rare-earth ion is shielded by 5s and 5p electrons of the outer shell, thus reduces the effect of its surrounding crystal field; while the perturbation of the crystal field may lead to transition of the originally forbidden 4f electron, and forms narrow bandwidth absorption and fluorescence spectrums. So the change of the trivalent rare-earth ions in different crystals is obviously different from transition metal ions.

Host crystals used in laser crystal are mainly oxides and fluorides. As a host crystal, it should have stable physical and chemical characteristics; it can easily generate large size crystal with good optical homogeneity and low price. At the same time, we should notice the adaptability between the host crystal and the active ions: for example, the radius, electro negativity and valence state between host positive ion and active ion should be close as possible. Besides, we should also take into account of the impact of host crystal field upon active ion spectrum. For some host crystal with special function, it can directly generate laser with certain special function after mixed with active ions; for example, in some nonlinear crystals, after generating laser, active ion can be directly transferred into harmonic wave output through host crystal.

JK Laser Drilling Solution

JK Lasers' JK and eCO2 laser products are suited to all kinds of drilling applications, such as small hole, irregular shaped hole, blind hole and taper hole. Laser is used to processing holes with severe angles and drill holes on difficult-to-process materials. Once set up, it can achieve hundreds of different sizes on 3D surface.

 
Advantages of laser drilling are:
non-contact process
high precision and good consistency
accurate control on calorific value
capability of drilling small hole with high aspect ratio
easy programming and suitable for automation
fast set up and few fixtures to improve production efficiency
flexible in samples' transformation and small batches production
universality
easy beam combining
drilling different shapes at the same time
applicable to various materials

JK laser series in pulse Nd: YAG laser can drill on metal, ceramic and graphite composite material. These lasers drill by generating discontinuous pulses which can control energy, peak power and local shape. Pulse YAG laser becomes comprehensive drilling system through the control of these pulse parameters. The key of drilling by pulse YAG laser is peak power. Even pulse YAG laser of low average power can make high quality holes, because the reaction between materials relies on peak power and pulse energy, not average power.


 
Source : thescienceofacne

Percussion drilling of Nd: YAG laser
The drilling size of percussion drilling is decided by the size of laser focus. In the drilling process, there is no relative movement between laser beam and components. Suitable pulse parameter and pulse quantity can make high quality hole. It can drill holes of 25μm-100μm diameter with different limits according to different materials and thickness. Most diameters are within 300μm-600μm. The adoption of special "high-speed" drilling can promote the speed of drilling. High speed drilling is usually applied in turbine engines components, which makes laser drill in a specific and continuous position around the component, launched by motion system encoder signal. If drilling a hole needs ten pulses, high speed drilling system will revolve the component ten times and  send out a pulse for each turn. The speed is promoted by the elimination of dislocation. Percussion drilling helps to control drilling conicity and improve drilling speed by improving the reaction between laser beam and materials. Pulse shaping is programming on partial pulse shape. It can also enhance drilling quality and speed by cutting a long pulse into three or four short parts; each parts is divided by a transient laser shutdown. The last laser needs longer time to cut the crumbs in the process. Use low peak power in the beginning of pulse can avoid bell mouth of hole.

Trepan of Nd: YAG laser
Trepan needs moving system, which is completed by the relative movement between penetrated laser and components. Diameter tolerance of trepan is half of percussion drilling, which can processing custom-built taper or change section shape in depth direction. It requires good moving precision and programming capability. Trepan can also make big hole of given shapes and make complex 3D finishing.

Drilling quality on metal is determined by drilling diameter tolerance, drilling conicity, thickness of recast layer and micro-crack. Diameter tolerance of percussion drilling is generally less then +/- 50μm while that of trepan is reduced to +/- 25μm. Recast is solidification of melted metal in inner-wall of hole; thickness of recast is usually less than 100μm, which is diverse for various alloy and hole depth. The maximum drilling depth is 50mm but most are within 15mm.

Work Theory of the Laser Cutting Machine

Laser has been applied in teaching, military as well as industrial production. Laser cutting machine is one of the applications. It can be used in both metal and non-metal cutting, Melting surface material by laser beam. This article will discuss the work theory of laser cutting machine.

Introduction on the work theory of laser cutting machine.

Laser cutting machine adopts the energy released on the time when laser beam irradiate metal surface. The metal is melt by laser and sinter is blow away by gas. Because laser power is highly focused, only a very little heat effects the other part of metal plate and causes a little or no deformation. Laser can cut any complex shape precisely, which needs no further processing.

Laser source is generally CO2 laser beam with operating power of 500～5000W. The power is even lower than that of many household electric heater, and because of lenses and reflectors, laser beams are focused in a very small bit of area. Highly focused energy heat the area quickly and makes the metal plate melted.

Laser cutting machine can cut stainless steal of thickness less than 16mm; when adding oxygen in laser beam, the cutting thickness is 8～10mm but it will generate a thin oxidation film in the cut surface. The maximum thickness is 16mm which leads to larger cutting deviation on the size of components.

Since the advent of laser, numerous laser products have been developed, such as laser printer, laser cosmetic instrument, laser marker, laser cutting machine etc. Due to its late start in China, the laser technology in China is greatly behind the developed countries. Although Chinese manufacturers can produce plenty of laser products, some key parts such as laser tube, driving motor, galvanometer and focus lens are imported products. This leads to an increase on cost thus an increase on consumer's payment.

In recent years, domestic research and production of  laser products become closer to advanced overseas products with the progress of laser technology in China. Some aspects are even superior to products abroad, which has a leading role in market because of the  advantages of price. Overseas products have absolute predominance in precision machining for its quality on stability and endurance.

Work theory of laser cutting machine

Laser tube is the core part of laser cutting machine. So, below is an introduction of the most popular laser tube. CO2 laser tube.

Laser tube is composed of hard glasses, so it is fragile. It adopts layer of sleeve construction with discharge tube in the most inside layer. However, the diameter of discharge tube is thicker than laser tube, diffraction between the thickness of discharge tube and the size of flare is in direct ratio; the length of tube is in proportion to output power of discharge tube.  Laser tube generates a large quantity of heat in the operation of laser cutting machine, which influences the normal work. So cold water machine is needed to cool laser tube, ensuring constant temperature for successful running.

Cutting features of laser cutting machine

Advantages of laser cutting:
One — high efficiency
Laser cutting machine is always connected to several numerically-controlled rotary tables to achieve numerical controlled cutting. It only needs to change the NC program to adjust to components of different shapes, which can make 2D cutting as well as 3D cutting.

Two — high speed
When cutting low carbon steel sheets of 2mm thickness, the speed of 1200W laser cutting is 600cmmin; when it is 5mm thick polypropylene resin plate, the cutting speed is 1200cmmin. The material needs no clamping fix in laser cutting process.

Three — high quality cutting
Laser cutting features thin kerf. The two sides of kerf are parallel and the kerf is vertical to the surface. The cutting precision can reach to ±0.05mm. The cutting surface is clean and nice, with roughness of tens of microns. The cut components can even come into use directly without further machining. After laser cutting, the heat effected area is very small and material near to kerf has not been affected, making little deformation, high cutting precicion and perfect geometrical shape.

Four — non-contact cutting
Laser cutting is non-contact cutting, which means no tool wear problem. When processing different shapes, there is no need to change tools, the only way is to alter the output parameter of laser. The whole laser cutting process features low noise, little vibration and little pollution.

Five — various cutting material
Compared to oxyacetylene cutting and plasma cutting, laser cutting can be applied on more materials, including metal and non-metal, metal matrix and non-metallic matrix composite, leather, wood as well as fibers.

Cutting methods of laser cutting machine
Vaporization cutting

It means that vaporization is the main way to remove the processed material. In the process of vaporization cutting, workpiece surface is heated to vaporization temperature quickly by focused laser beams, forming High pressure steam and spraying outward at supersonic speeds. In the meantime, a hole is formed in the laser active area and laser beams reflex several times in the hole to increase the absorption of laser by material.

When high-pressure vapors spray outward, the melted materials are blown away in the kerf till the workpiece is finally cut. Vaporization cutting needs very high power density, which is eighth power of ten watt above per square centimeter. It is usually applied in low flash point materials and refractory materials.

Reaction Fusion Cutting
When assistant airflow not only blows the melted materials from the kerf but also has thermal reaction with the workpiece, this is the so-called reaction fusion cutting. Gases that can have reaction with workpiece are oxygen or mixture gases containing oxygen. When the surface  temperature of workpiece reach to ignition temperature, strong combustion heat release occurs to improve the laser cutting ability.

Combustion heat release of low carbon steel and stainless steel is 60%. And it is about 90% for reactive metals like titanium.

Compared to vaporization cutting and general fusion cutting, reaction fusion cutting need less laser power density. However, reaction fusion cutting may effect the performance of worpiece since the combustion reaction can lead to chemical reaction on materials.

Fusion Cutting
When adding a assistant airflow system coaxial with laser to  blow the melted materials away from kerf, this kind of cutting is fusion cutting. In fusion cutting, workpiece needn't to be heated to vaporization temperature so the required laser power density is reduced greatly.

Laser Scribing
It is mainly used in semiconductor materials, in which laser of high power density make a shallow groove in the semiconductor materials of the workpiece and then makes it crack through mechanistic or vibratory methods. The quality is valued by the surface fragments and size of heat affect area.

Cold Chipping
It is a new processing method, which is put forward along with ultraviolet band superpower excimer laser appeared in recent years. The basic theory is that energy of ultraviolet photons is similar to binding energy of many organic materials; this high-energy photons are used to impact bond organic materials thus make it crack, achieving purpose of cutting. This new technology has promising application future, especially in electron industry.

Thermal Stress Cutting
Mechanism of thermal stress cutting is that laser beams heat an area of fragile material to produce evident temperature gradient. The high surface temperature makes expansion and inner lower temperature hinders expansion, forming pulling stress in the surface and radial crushing stress inside. When the two stresses exceed fracture limit strength of the workpiece, crackle appears. And then the workpiece is broken along the normal direction of the crack. It is suitable for glasses and ceramics.

Conclusion: laser cutting machine is a cutting technology of melting and gasifying surface material through focused energy generated by the use of laser specialties and focused lens. It features good cutting quality, high speed, various cutting material and high efficiency.

Functions and Application Fields of Flying Laser Marking

Flying laser marking is playing an important role in industrial equipments, which is no longer for simply purpose of showing product date and lot number. Flying laser marker can be applied in the production in daily life, such as medical health products, food and beverage, tobacco, liquor, electron industry, automobile parts, crafts, dress accessory, etc.. It can also be applied in biological pharmacy and building materials fields and it will cover more fields in the future. Below are the functions and application fields of flying laser marker:

1. Image carving
Flying laser marker is different from traditional laser marker, since it is no longer limited to singular surface word inking; it has been developed for popular image and words carving. Static laser polishing machine can complete one action in a single operation. While flying laser marker can move based on one-way axis and carve at the same time by the adoption of vector marking.

2. Driving inkjet operation
Flying laser marker jumps out of the initial singular character market and marches into the unique visual and touch sensation  market competition of inkjet machine. It is no longer plain character but image-text market. It has changes in aesthetic feeling as well as in practicability such as anti-fake and anti-channel conflict characteristics.

3. Specification and classification of flying laser marker
CO2 laser marking is mainly used on non-metallic material such as paper, leather, acrylic, glass, plastic and wood. YAG laser marking is mainly applied in fields like household instrument and electronic instrument, which can be connected to internet and scan and carve image in high speed. Semiconductor laser marker has very high speed of light conversion rate, and it belongs to maintenance-free product since its light source is semiconductor. Fiber laser marking has two types: continuous fiber laser and pulse fiber laser. It is the most advanced equipment features small volume, high speed and high quality light beam.

4. Industrial efficiency of flying laser marker
The traditional laser marker can only inkjet and mark on static objects, which brings waste of energy and seriously repeated work of production staff. While the new flying laser marker has remarkable efficiency as well as features a saving quality of labor, time and energy. Flying laser marker has gained great attention in market. Because of the perfect marking effects, It can be well accepted by the market.

5 Useful Tips For Buying A Laser Marking Machine

As known to most consumers, Laser marking machine can dramatically improve production efficiency and quality as the most advanced laser marking equipment. Faced with so many laser equipment firms, how to select the most satisfied one is a question to many customers. Below are five points for choosing a laser marking machine.

1. Consider the marking material. There are various types of laser marker according to different laser, such as optical fiber and CO2. Customers need to choose the right type for metal and non-metallic products.

2. Select Laser marking machine according to the processing demands of workpiece. Generally speaking, there are three application ways of laser machinery, including carving, cutting and marking. There are special-purpose machine and multi-functional machine, which should be chosen according to the primary demands.

3. Size of format should match with the size of workpiece. Not all the biggest format is the best when it comes to the choice of format size. On one hand, larger format means more cost; on the other hand, some low quality laser marking machine has unstable average degree of laser output on large format, causing irregularity defect. So the appropriate format is correct choice.

4. Pay more attention to company qualification than contract and price. There are different focuses for different types of laser marker, like UV laser marking machine, optical fiber laser marking machine and CO2 laser marking machine. It is necessary to check the related license of company, certification of laser equipment and qualification certificate of engineer.

5. Except for company qualification and product quality, after-sale service is another thing to be valued. For example, whether there is on-site installation and rapid debugging. Whether they offer free specialized guidance to ensure proficiency of the operator. Whether there is quality assurance services for the whole machine.