Solid

Nd:YAG

YAG (yttrium, aluminum, garnet)

Basic wavelength (1064 nm)

• Mainly used for general-purpose engraving

Frequency doubled (532 nm) (green laser)

• Used for engraving on materials such as silicon wafers

  Used for fine printing and processing

Frequency tripled (355 nm) (UV laser)

• Used for ultra-fine processing such as LCD printing, repair processing, VIA via processing

  LCD repair process … the process of removing the resin coating for repair

  VIA via processing … hole processing of printed circuit boards

YAG laser (Nd:YAG)

YAG lasers are commonly used in various marking applications, such as marking on plastic and metal workpieces, as well as machining applications. YAG lasers emit an invisible near-infrared beam with a wavelength of 1064 nm.
YAG is a solid yttrium aluminum garnet with a crystal structure. After adding a luminescent element, in this case Nd (neodymium), the YAG crystal enters an excited state after absorbing the light emitted by the laser diode.

Nd:YVO₄ (1064 nm)

YVO₄ (yttrium vanadate)

• Used for ultra-fine text marking

  High peak energy obtained by high Q-switching frequency

  Good energy conversion efficiency

YVO₄ Laser (Nd:YVO₄)

YVO₄ Laser can be used for ultra-fine marking and machining applications. The YVO₄ laser emits an invisible near-infrared beam at a wavelength of 1064 nm, the same as the YAG laser.
YVO₄ is a Y(yttrium)V(vanadium)O4(oxide), or YVO₄(yttrium vanadate) solid with a crystal structure. After the addition of a luminescent element, in this case Nd (neodymium), the YAG crystal enters an excited state after absorbing the light from the laser diode.

Yb: Fiber (1090 nm)

Yb (Yttrium)

• For high-output imprinting

  The surface area of ​​the amplification medium is very large, and high output can be easily achieved

  High cooling efficiency, which can simplify cooling equipment and achieve miniaturization

LD (650 to 905 nm)

• Semiconductor laser (GaAs, GaAlAs, GaInAs)

Gases

CO₂ (10.6μm)

• For machining equipment, marking, laser surgery

CO₂ Laser

CO₂ Laser is mainly used for machining and marking applications.
CO₂ Laser emits an invisible infrared beam with a wavelength of 10.6μm. N2 nitrogen can be used to increase the energy level of CO₂ , and helium can be used to stabilize the energy level of CO₂ .

He-Ne laser (630 nm)
Generally (red)

• Used for measuring instruments (shape measurement, etc.)

  Used for common laser measuring instruments on the market (used for shape measurement, etc. because of low output power)

Excimer laser (193 nm)

• Used for semiconductor light leakage equipment and ophthalmic medical treatment

  Laser can be generated with a relatively simple structure by mixing inert gas and halogen gas

  Deep ultraviolet laser (DUV) has a very high absorption rate

  (In ophthalmology, vision is corrected by evaporating the lens and focusing on the retina)

Argon laser (488 to 514 nm)

• Used in physics and chemistry

  Can produce various colors, mainly used in biological research

Liquids

Dye (330 to 1300 nm)

 

• Used in physics and chemistry

  The laser makes the stimulated pigment emit fluorescence

Wavelength: 10600 nm

The wavelength of CO₂ laser is ten times longer than that of YAG, YVO₄ or fiber laser. This is the longest wavelength among the widely used industrial lasers. As the name suggests, it is produced by exciting CO₂  gas as the laser medium.

Typical characteristics of lasers in the 10600nm wavelength region

• Not absorbed by metals
• The object may melt or burn due to heat transfer at long wavelengths.
• Transparent objects such as glass and PET can be processed.
• CO₂  lasers have difficulty in achieving color contrast printing on resins compared to lasers with basic wavelengths.

Wavelength: 1064 nm

IR is the abbreviation of Infrared Ray, and its wavelength is the most widely used wavelength in laser processing. As the name suggests, IR is the spectrum of the area outside the red region, (that is,) IR has a wavelength greater than 780 nm and cannot be seen with the naked eye. But it does not mean that IR is 1064 nm.

General characteristics of lasers in the 1064 nm wavelength region

• Wide range of processing applications - from resins to metals
• Transparent objects, such as glass, cannot be processed because lasers easily pass through them.
• It is easy to discolor the resin

Wavelength: 532 nm

The wavelength of the double-harmonic generation (SHG) laser is half of the standard wavelength (1064 nm). 532 nm is in the visible spectrum and is green. The wavelength is generated by emitting light with a wavelength of 1064 nm and passing through a nonlinear crystal to reduce the wavelength by half. The reason why YVO₄  medium is often used is that its beam characteristics are suitable for complex and delicate processing.

Typical characteristics of 532 nm wavelength lasers

• It can be absorbed by various materials, including gold with high reflectivity, and copper can also be easily processed.
• Because it has a smaller beam spot than IR lasers, it can perform fine processing.
• It cannot generally process transparent objects.

Wavelength: 355 nm

The wavelength of a triple-harmonic (THG) laser is one-third of the fundamental wavelength of 1064 nm, in the ultraviolet (UV) region of light. The fundamental wavelength is generated using a YVO₄ or YAG laser, then converted by a nonlinear crystal to 532 nm, and then by a second nonlinear crystal to 355 nm.

Typical properties of a 355 nm wavelength laser

• Most materials have a very high absorption rate without generating excessive heat.
• The very small beam spot enables ultra-fine processing.
• Its high absorption rate affects the optical crystal, and it consumes more maintenance costs and consumables than other wavelength lasers.

Laser Oscillation Principle

Here is an explanation of the principle before the laser is oscillated.

1. Absorption

When external light enters, the electrons in the atoms absorb the light and enter a high-energy state from the lowest energy state (ground state). As the energy increases, the electrons move from the normal orbit to the outer orbit. This state of increased energy is called "excited".

Atomic state

Electronic state

2. Natural emission

The excited electrons, under the action of the absorbed energy, have their energy levels raised. After a certain relaxation period, the electrons with raised energy levels want to stabilize, so they release energy to return to a lower energy state. At this time, the energy is released in the form of light with the same energy. This phenomenon is called "natural emission".

Atomic state

Electron state

3. Stimulated emission

As shown in the figure below, when electrons in a high energy state emit light with the same energy as the light they hold, the emitted light has exactly the same energy, phase, and direction of motion. In other words, one photon becomes two photons during emission. This phenomenon is called "stimulated emission". The light produced by stimulated emission has the same energy, phase, and direction of motion. Therefore, a large amount of light produced by stimulated emission can produce strong light when the above three elements are set in the same way. Lasers are produced by amplifying incident light using the stimulated emission phenomenon. Therefore, it has the characteristics of (1) monochromaticity (all light energy is equal), (2) coherence (same phase), and (3) high directionality (same direction of motion).

Atomic state

Electron state

4. Population inversion state

To utilize the natural emission oscillation laser beam, the electrons in the high energy state must be increased to a density that is overwhelming that of the electrons in the low energy state. This phenomenon is called "population inversion state". In other words, when the amount of natural emission light exceeds the absorbed light, laser beams can be effectively generated for the first time.

Electrons in a population inversion state

• ＝More electrons in high energy state
• ＝Fewer electrons in low energy state

5. Laser oscillation

In a population inversion state, when one electron emits light naturally, the light causes a different electron to emit light naturally.
The resulting chain reaction increases the amount of light and produces a strong beam. This is how laser oscillation works.

Electrons in a population inversion state

In order to achieve population inversion, pumping and specific working materials are usually required.

Pumping is a process that uses light to raise atoms from the ground state to an excited state (usually a metastable state). The light source for the pump should meet two basic conditions:

1. It has a high luminous power

2. The spectral characteristics of the radiation light as the pump source should match the absorption spectrum of the laser working material.

 

 

Take the ruby ​​laser as an example. Its excitation light source is a spiral pulsed xenon lamp, and the working material is a ruby ​​rod. The xenon lamp has a strong light output in the green and blue spectrum, which just corresponds to the absorption spectrum of ruby, and finally makes the ruby ​​rod produce a large number of excited (metastable) atoms, realizing the inversion of the number of particles. The ruby ​​used as the working material needs to be made into a cylindrical rod with two parallel end faces and silver-plated, so that one end becomes a 100% total reflection surface and the other end becomes a 90% partial reflection surface (which can be regarded as an optical resonant cavity).

Most lasers are composed of a pump source, a working material, and an optical resonant cavity. An optical resonant cavity is usually composed of two reflectors at a certain distance apart (one is a total reflection surface,

the other is a partial reflection surface). This allows the incident light source to oscillate back and forth in the resonant cavity, contacting the working material as much as possible, increasing the probability of stimulated radiation of atoms in the working material.

Finally, a laser beam with strong directionality, high brightness, good monochromaticity and coherence will be emitted from the other end of the partial reflection mirror.

Laser Oscillator Tube Components

Three Components of Laser Oscillator Tubes

Various laser oscillator tubes are composed of the following three components:

1. Laser Medium
2. Excited Source
3. Amplifier

1. Laser Medium
2. Excited Source
3. Amplifier