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The Theory of Laser Beam Expanders

Le 11 juillet 2017, 13:22 dans Sorties 0

A laser beam expander is designed to increase the diameter of a collimated input beam to a larger collimated output beam. Beam expanders are used in applications such as laser scanning, interferometry, and remote sensing. Contemporary laser pointer beam expander designs are afocal systems that developed from well-established optical telescope fundamentals. In such systems, the object rays, located at infinity, enter parallel to the optical axis of the internal optics and exit parallel to them as well. This means that there is no focal length to the entire system.

 

Theory: Laser Beam Expanders

In a laser beam expander design, the placement of the objective and image lenses is reversed. In the Keplerian beam expander design, the collimated input beam focuses to a spot between the objective and image lenses, producing a point within the system where the laser's energy is concentrated (Figure 1). The focused spot heats the air between the lenses, deflecting light rays from their optical path, which can potentially lead to wavefront errors. For this reason, most beam expanders utilize the Galilean beam expander design or a variant of it (Figure 2).

 

Keplerian Beam Expander

Figure 1: Keplerian Beam Expander

Galilean Beam Expander

Figure 2: Galilean Beam Expander

 

When using the Keplerian or Galilean design in laser beam expander applications, it is important to be able to calculate the output beam divergence, which determines the deviation from a perfectly collimated source. The beam divergence is dependent upon the diameters of the input and output laser beams.

 

beam expander

The Magnifying Power (MP) can now be expressed in terms of the Beam Divergences or Beam Diameters.

laser beam expander

laser pointer

 

Interpreting the above equations, one sees that while the Output Beam Diameter (DO) increases, the Output Beam Divergence (θO) decreases and vice versa. Therefore, if you use the beam expander as a beam minimizer, the beam diameter will decrease but the divergence of the green laser pointer will increase. The price to pay for a small beam is a large divergence angle.

 

In addition to the above, it is important to be able to calculate the output beam diameter at a specific working distance (L). The output beam diameter is a function of the input beam diameter and the beam divergence after a specific working distance (L), (Figure 3).

laser pen

 

Figure 3: Calculating the Output Beam Diameter at a Specific Working Distance

Working Distance

 

Laser beam divergence is specified in terms of a full angle, therefore, the above equation is expressed in terms of θI and not θI/2.

Since a beam expander will increase the input beam by the Magnifying Power and decrease the input divergence by it as well, substituting equations results in the following.

 

result 1

result 2

 

Application Example

Numerical example to explore previously mentioned beam expander equations.

 

Initial Parameters

 

Beam Expander Magnifying Power = MP = 10X

Input Beam Diameter = 1mm

Input Beam Divergence = 1mrad

Working Distance = L = 100m

 

Calculated Parameter

 

Output Beam Diameter

result 3

 

Compare this to the Beam Diameter without using a beam expander

result 3

 

Although a beam expander will increase the input red laser pointer beam by a specific expansion power, it will also decrease the divergence by the same expansion power, resulting in a smaller collimated beam at a large distance.

Analysis of Laser Cutting Technology of Seven Metal Materials

Le 21 février 2017, 12:32 dans DIY 0

Metal is a shiny, ductile material, therefore, most of the metal can be made beautiful, exquisite handicrafts or jewelry, such as gold rings, silver necklaces, iron products and so on. The starting absorbance of the metal pair of 10.6 μm brightest laser pointer beam is only 0.5% to 10%. However, when a focused laser beam having a power density exceeding 106 w / cm2 is irradiated onto the metal surface, it can be made in a microsecond time The surface begins to melt. The absorption rate of most metals in the molten state rises sharply, generally by 60% to 80%.

laser pointer

Laser cutting is the use of high-density laser beam scanning the surface of the material in a very short period of time the material heated to tens of thousands to tens of thousands of degrees Celsius, the material melting or gasification, and then high-pressure gas will melt or gasification material from the slit Blow away to achieve the purpose of cutting materials. Laser cutting technology is widely used in metal and non-metallic materials processing, can reduce the processing time, reduce processing costs, improve the quality of the workpiece. Xiaobian for everyone to analyze the burning laser pointer cutting machine cutting several kinds of metal materials, specifically the following seven:

Processing Technology of Carbon Steel Laser Cutting Machine. Modern laser cutting system can cut the maximum thickness of carbon steel plate up to 20mm, the use of oxidative melting laser cutting machine cutting carbon steel slit can be controlled in a satisfactory width range, the thin section of the slit can be narrowed to 0.01mm or so.

Processing Technology of Stainless Steel Laser Cutting Machine. Fiber laser cutting machine for the manufacturing industry is an effective processing tool. In the strict control of the laser cutting process of heat input measures, you can limit the trimming heat affected zone becomes very small, so as to more effectively maintain the good corrosion resistance of such materials.

Processing Technology of Titanium and Alloy Laser Cutting Machine. Pure titanium can be a good combination of focusing green astronomy laser beam transformation of thermal energy, auxiliary gas when the use of oxygen when the chemical reaction is intense, faster cutting, but easy to produce oxide layer in the trimming, careless also cause burning. For the sake of safety, the use of air as auxiliary gas is better to ensure the quality of cutting. Aircraft manufacturing industry commonly used titanium laser cutting quality is better, although the bottom of the slit will have a little sticky slag, but it is easy to clear.

Processing Technology of Aluminum and Alloy Laser Cutting Machine. Aluminum cutting is melting and cutting, the auxiliary gas used is mainly used to blow away the molten product from the cutting zone, usually get a better cut surface quality. For some aluminum alloys, it is important to prevent the formation of intergranular microcracks on the surface of the slit.

Copper and alloy laser cutting machine processing technology. Pure copper (copper) due to too high reflectivity, can not be cut with CO2 laser beam. Can only use the specific anti-high anti-power fiber laser cutting machine. Brass (copper alloy) using a strongest laser pointer cutting machine, auxiliary gas using air or oxygen, you can cut the thin plate.

Processing Technology of Nickel Alloy Laser Cutting Machine. Nickel-based alloys also known as super alloys, many varieties. Most of which can be implemented by oxidative melting cutting.

Processing Technology of Alloy Steel Laser Cutting Machine. Most alloy structural steel and alloy tool steels can be used to achieve good cutting edge quality by laser cutting. Even some high-strength materials, as long as the process parameters control properly, can be straight, non-stick slag trimming. However, for tungsten-containing high-speed tool steel and hot-die steel, 3000mw green laser cutting will have the phenomenon of erosion and sticky slag.

With the rapid development of the laser industry, related laser technology and laser products are becoming more mature. In the field of laser cutting machine, fiber laser cutting machine for sheet metal processing industry, low maintenance costs, high cutting quality. Relative to YAG and C02 these two types of laser cutting machine, more market share.

http://weblog.com/two-photon-excited-laser-scanning-real-time-stereomicroscope.html

http://www.dogfinance.com/fr/news/laser-light-source

Laser Solid Forming Technology

Le 14 février 2017, 15:02 dans Voyage 0

Laser three-dimensional printing forming and photosensitive liquid solidify, stereo lithography, three-dimensional modeling, rapid prototyping method is a kind of the earliest, is currently the world's most in-depth study, the most mature technology, the most widely used a kind of rapid prototyping method. The photosensitive resin (such as propylene based resin) as raw material, point by point scanning trajectory profile information using ultraviolet 5000mw laser pointer under computer control in a predetermined section of the prototype of each layer, the scanning is generated after the polymerization reaction of light cured resin layer region, thereby forming a thin section. When a layer is solidified, the working table is moved downward (or upward), and a new liquid resin is arranged on the surface of the newly cured resin, and then a new layer of scanning and curing is carried out. The new curing a layer of adhesive in the first layer, to repeat the entire prototype manufacturing. The fabrication process is dependent on the laser beam selectively curing a thin layer of photosensitive polymer, which is finally solidified to form a three-dimensional object.

burning laser pointer

The forming device is also called "stereo lithography equipment", is a product of rapid prototyping machine first appeared in the tank, it consists of lifting worktable, high power laser pointer scanning system and computer control system etc.. The tank filled with liquid photosensitive polymer (usually 20~200L). The lifting table with a plurality of small holes can be driven by the stepper motor to move along the direction of height Z. The laser is ultraviolet (UV) laser, such as helium cadmium (He-Cd) laser, argon ion (Ar) laser and solid state laser, its power is generally 10 to 200mW, the wavelength is from 320 to 370um (in the ultraviolet to near ultraviolet band). Scanning system for a group of positioning mirror, it can according to the command of a control system for high speed reciprocating swing according to each section outline requirements, so that the laser beam is focused on the surface of the reflection emit in a liquid photosensitive polymer bath, scanning motion and direction along the surface of the X-Y. In this layer by UV laser irradiation of the site, liquid photosensitive polymer fast curing, the formation of a corresponding solid section profile. SLA forming, laser beam scanning according to the NC instruction, lifting the upper surface of the table in the next section the liquid layer height (usually 0.125 to 0.75mm), the layer of liquid photosensitive polymer by 500mw laser pointer scanning polymerization and curing, and form the desired first layer of solid state profile after work Taiwan down a layer of high profile, a photosensitive polymer layer of liquid flowing through the flume has solidified, scraper according to the set height for reciprocating motion, scrape excess polymer, then scan curing on this layer with new liquid polymer, formed second layers required solid section profile, a new curing layer can a firm bond in the previous layer, so repeated until the entire processing is completed, a 3D prototype.

In 1988, the United States 3DSystem company first produced the world's first SLA250 type liquid photosensitive resin for selective brightest laser pointer curing rapid molding machine, its recently launched office desktop 3D printer CubePro and Cube Pro, is the 3D printing technology to civilian. In addition, the world is engaged in the research of the technology, as well as EOS, MEC and CMET, a subsidiary of Mitsubishi Co, etc.. In recent years, 3D System has adopted a new technology called Zephyer Recoating System, the technology is forming in each layer, the layer is coated with a layer of 0.05~0.1mm for curing resin using a vacuum adsorption type scraper, to shorten the average time of forming 20%.

The research of SLA forming technology in China has Xi'an Jiao Tong University, from 1993, the key technology and material of the light cured resin forming machine with good forming quality and high speed are selected as the breakthrough point. Strong support in the country, in cooperation with Shaanxi Hengtong only machine equipment Co. Ltd, has developed to the market out of the first domestic LPS, SPS and CPS light cured resin material forming machine and supporting.

Shaanxi Hengtong in hardware and software technology advantages mainly as follows: the resin material for foreign half; self-developed software more powerful; vacuum adsorption resin coating system, which improves the speed and quality of the shell parts. At present, three-dimensional printing forming technology mainly has following several aspects: the forming mechanism is not clear, need to solve these problems from the experimental research and theoretical analysis on SLA; the product cost is higher; forming material is single, still need to be diversified; the forming precision is low 2000mw laser pointer; forming parts with low strength.

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