FAQs

Just the FAQs!

 

Frequently Asked Questions on Laser Machine Tools

 

 

1. What does YAG mean?

Yttrium Aluminum Garnet. A type of solid-state laser material. Actually, a laser rod. A crystal.

 

2. What’s Nd:YAG?
The YAG crystal is doped with Neodymium, chemical symbol, Nd. It is about 2 percent Nd and 98 percent YAG. YAG is the host, simply there to hold the Nd ions that do the lasing in a crystalline lattice framework.

 

3. What are solid state lasers?
The lasing material is a solid (such as YAG, vanadate, glass and ruby). Other types of lasing materials are gases and liquids. The first working laser was ruby, developed by Dr. Ted Maiman at Hughes Malibu before 1960. YAG began to replace ruby by 1970. YAG is energized (pumped) by a lamp, called optically pumped. If pumped by a diode laser, the crystal can be vanadate. Rod Waters, Founder of Laserod, was fortunate to have worked for Dr. Maiman at his company, Korad Lasers, in Santa Monica, California.

 

4. What are gas lasers?
Some popular gas lasers are CO2, excimer, helium neon, argon and krypton. They are usually pumped by electrical discharge through the gas contained in a glass or metal tube.

 

5. Why does Laserod prefer solid state lasers?
They are far more compact than gas lasers such as excimer and CO2. YAG, at one micron wavelength, is between CO2 at ten microns, and excimers in the short wavelength UV region. Wavelength is directly related to laser cutting width. The shorter the wavelength is, the more narrow is the cutwidth.

 

CO2

Laser

YAG

Laser

Excimer

Laser

Wavelength

(microns)

10.6

1.06

0.248

Spot Size

(microns)

120

12

3

 

 

6. Trepanning is a curious word. From whence does it come?
Brain surgeons trepan, or saw, a circular bone segment out of a skull, do their thing, then replace the segment and sew up the patient. Laser machinists swing their beam in a circle, thereby drilling a hole. As opposed to percussion drilling.

 

7. What is the minimum feature size that can be produced by laser micromachining?
A width of slightly less than one micrometer. But this is for thin coatings under one micron thickness. A typical value is 10 microns laser cut width for deeper beam penetrations.

 

8. How “micro” do you expect laser micromachining can do in the future?
A rule of thumb is about one laser wavelength, or 1 micron for YAG, 0.5 micron for frequency doubled YAG and 0.25 micron for frequency quadrupled YAG. These numbers are for cut widths in thin coatings. Multiply by 10 for deeper beam penetrations.

 

9. What’s the meaning of tolerance, resolution, accuracy and precision?
Tolerance is the acceptable deviation from specification.

 

Resolution is the minimum increment to which a measurement can be made. For us, this is a design parameter of the X-Y stage motion encoders or galvo.

 

Accuracy is how close a measurement is to the “true” value. “Truth” is the traceability of the measurement to a primary standard at NIST, a USA governmental agency, National Institute for Standards & Technology. For us, this is conformance to our customer’s metrology.

 

Precision is repeatability. For us, precision is half the increase in laser line width or hole diameter when the laser is run repeatedly over the same part a number of times.

 

All are plus/minus numbers except resolution.

 


YAG, CO2 and Excimer Lasers Compared (as Industrial Lasers)

 

YAG is an acronym for Yttrium Aluminum Garnet, a crystal doped with the rare earth element, Neodymium, abbreviated as Nd:YAG or simply “YAG.” Nd does the lasing, YAG is the host for the Nd. The crystal, called a laser rod, is mostly YAG, only a few percent Nd. A nice characteristic of solid state lasers like YAG is safety. There are no compressed or lethal gasses. Another crystal, vanadate, is used. Loosely speaking, we call it YAG for convenience.

 

Solid state lasers were the first to be invented (1960), CO2 in 1964 and excimer in 1970. YAG, a solid state laser, has the most experience. Laserod has years of experience in all the major YAG types: lamp, fiber and diode.

 

Both CO2 and excimers are mixtures of various gases. CO2 is a source of far infrared (IR) radiation only. Excimers are ultraviolet (UV) sources only whereas YAG is multi-wavelength from near IR to UV. YAG is therefore more versatile.

 

Both carbon dioxide (CO2) and excimer are gas lasers. Solids are denser than gases. YAG is more compact than either of the large and bulky gas lasers. However, Laserod’s principle holds a patent on a compact excimer whose laser head is only a few feet long. And Synrad, a CO2 supplier, offers low power compact CO2 sources. Each laser type has it’s unique applications. For example excimers are used in semiconductor wafer lithography and are famous for eye surgery. But the vast majority of lasers in the world are solid types: computer hard drives and DVDs. But the majority of industrial lasers are CO2.

 

YAG vs CO2 and Excimer:

 

There are more than 500 laser job shops in the United States. Most specialize in CO2 lasers. Our specialty is YAG. Excimer houses are even more rare. CO2 and YAG are expensive, but excimers tend to be more expensive. The most expensive laser to operate is excimer with UV diode pumped type coming in as a close second. High power industrial excimers are jokingly said to require PhDs for maintenance; UV YAGs require no maintenance, just diode replacement.

 

The big difference between YAG compared to CO2 lasers is the narrow kerf of less than 0.001 inch (25 microns). Therefore, YAG permits precision machining. Because of the 10:1 wavelength difference, CO2 lasers, as a rule of thumb, have a kerf ten times greater than YAG for the same beam delivery optics. Two examples of optics are fixed beam with moving part and galvanometer (galvo) moving beam. It’s possible to combine a galvo and an X/Y stage or a galvo and a moving web to both move the beam and the part. Both CO2 and YAG lasers integrate well into these devices.

 

More YAG versus CO2 differences are:

 

  • wavelength: YAG’s fundamental wavelength is 10 times smaller and produces relatively slag free cuts. YAG can be frequency multiplied (wavelength divided), CO2 cannot. When frequency tripled to the UV, YAG produces a kerf 30 times smaller. Doubled to the green, it’s 20X smaller.
  • peak power: YAG has many orders of magnitude higher peak power (by Q-switching) producing cleaner and smoother cuts due to higher vaporization temperatures. Yet in spite of the higher focused beam temperature, thermal effects are usually negligible. CO2 is not normally Q-switched. Laser peak power is pulse energy divided by how long the laser pulse lasts — femtoseconds to milliseconds.
  • average power: Both are available at multi-kilowatt average powers – which is laser energy delivered per second. By comparison, peak power is energy delivered per pulse.
  • efficiency: CO2 is easily an order of magnitude more efficient than YAG but this is mainly important to scientists, not us machine tool makers.

 

 

YAG vs Excimer and CO2:

 

  • frequency multiplication of YAG from IR to green (1064 to 532nm) and to UV at 355nm allow YAG lasers to compete with excimers.
  • pulse rate of excimer is typically 100 pulses per second (Hz) compared to up to 400,000 for one of our YAGs.
  • pulse energy of excimer can be joules. YAG is millijoules. These orders of magnitude differences in energy and speed make for vastly different applications.
  • applications: low power CO2 is good for thick plastics, high power for thick metal cutting. YAG is good for thin metal cutting and UV YAG for thin plastics. But YAG cuts are cleaner. Q-switched YAG lasers excel in high precision line ablation compared to excimers as area ablators. Consider plated surfaces – a metallized coating of gold, copper, or ITO for example – are easily ablated or patterned by either YAG or excimer. YAG excels as a line scriber, excimer for ablation of small pattern areas. YAG can pattern a thin coating up to 1.6m x 1.6m whereas excimer is an order of magnitude smaller. CO2 lasers cannot ablate copper or gold. Feature size of excimer can be submicron whereas YAG is 10um.

 

The choice of which laser to use is application specific. It comes down to what works best for a given job. Our job is to prove what works for you.

 

You may call us, fax us or e-mail your requirements. Typically, send us a sketch or dxf via e-mail. In most cases you supply the material. We will quote on a turnkey basis. Prototypes are welcome! We sell systems as well as offering a laser processing service.

If you have any further questions that were not answered above, please contact us directly at Laserod.