Laser materials processing
04 Guidance and Focussing of Laser beams
04 Guidance and Focussing of Laser beams
Which part of the laser beam is known as "focus depth" ?
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Wich two optical elements can be used for focusing a laser beam? (in case of YAG- and CO2-Lasers)
YAG-LAsers:
Lens-optics, consisting of glass.
CO2-Lasers:
Lens-optics, consisting of ZnSe (Zinc-selenide, Zinkselenit), are in use in case of lower laser-powers up to ca. 5 kW. The employment of ZnSe with higher laser powers leeds to an increasing danger of self-combustion (Selbstentzündung) of the lens due to the amount of laser-energy absorbed by the ZnSe-material.And: The combustion-products of ZnSe are harmful ! (note: Here glass as lens-material is not possible due to the CO2-lasers wavelength.) Therefore, in case of higher laser-powers (> 5 kW) mirror-optics are in use for the focussing of CO2laser-beams (mostly parabolic-mirrors).
Beam-Guidance to the workpieces via free-propagation:
Wich benefits are resultig from a short beam-path (<2m)
.
The short path between laser-resonator and focussing-lens is beneficial in several ways:
•Divergences Omega0 of the raw beams don´t lead (along the short path) to unwished changes of their diameters.
•No (or rare) optical elements for the beam-guidance (e.g. mirrors), thus low dangers through dust etc.
•To maintain laser-safety only short metallic tubes around the beam-path are necessary.
•Misalignment-dangers (Dejustiergefahren) between laser and lens are low (intercept-theorem [Strahlensatz] with short lengths! ). Therefore justifiable (vertretbar) low mechanical complexity (Aufwand) for a stable and rigid beam-guidance.
How are laser beams transported over longer (>2m) distances ?
Distinguish between the different types of lasers.
Beams of YAG- or Diode-lasers would be guided on longer paths via light-conducting-cables.
In the case of longer beam-paths between laser and workpiece, a beam-guidance via free-propagation is only used with CO2-lasers.
Wich spechial complexities has to be mentioned in case of longer beam-guidance via free propergation (using a high power CO2-laser) ?
- Limiting the divergence of the raw beam via Telescopes
- Constant-keeping (Konstanthaltung) of the raw beam´s diameter D and its divergence at the location of the focussing-element (am Ort des fokussierenden Elementes) via a “BeamTrombone”(“Strahlposaune”)
- Measures against dangers of dirt and misalignment
Name the main benefits of using light-conducting-cables (fiber-cabels)
- No danger of dirt-pollution along the beam´s path
- Laser-safety is reached simply: The cable has a plastic covering (wrapping), that can be checked against its through-melting via integrated electrical signal-wires
- No misalignment-dangers: The cables are flexible and follow all movements
Why are there bending restrictions for light conducting cables and how are these restrictions technicaly achieved?
Bending restriction: for guiding a beam through a LLK total reflection on the casing is required. If the bending radius passes a certain limit, total reflection is not longer possible.
Bending Radius limitations: for this purpose „bending-radiuslimiters“are part of the outer shielding-covers of the LLK (e.g. Kevlar-fibers).
Wich angle is crucial for incouppling a laser beam into a light conducting cable?
angle of aperture
Wich two different types of light conducting cables are relevant for materials processing ?
Wich one is the most important one?
1. Step Index Fibrer --> (most important one)
2. Gradient Index Fiber
Wich reasons for unsing a monitoring device can you think of?
- During the programming of the machinery along the edges of a workpiece (control)
- During the laser-materials-processing: e.g. observing the luminous-effects (Leuchterscheinungen) of the processing and the comparison of those observed during successful processings. Often used as quality-proofs during processes with quality-documenting-obligations.
Describe the principle setup of a laser guidance unsing a LLK.
.
How can you calculate the focus diameter of a laser beam after leaving a LLK?
-
How is a high beam-quality defined?
Which benefits reslt from a high beam-quality?
High beam-quality: long focus-length (Rayleigh-length)
Benefits:
- better accessibility to the workpiece (e.g. entering into a bore-hole)
- advantageous for ar„emote-beamguidance“(„Remote-Strahlführung)
Special Optics:
How can you achieve a twin focus?
.
Special optics:
Explain the functionality of 1- and 2-dimentional scanning optics
The beam ist guided via mirrors into the different directions.
Name one example for the use of 1-dimentional and and one examlpe for the use of 2-dimentional scanning optics.
1-dim.: Optics for laser hardening
2-dim.: Optics for "remote-laser-weldung"
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Cartes-fiches
Which part of the laser beam is known as "focus depth" ?
-->
Wich two optical elements can be used for focusing a laser beam? (in case of YAG- and CO2-Lasers)
YAG-LAsers:
Lens-optics, consisting of glass.
CO2-Lasers:
Lens-optics, consisting of ZnSe (Zinc-selenide, Zinkselenit), are in use in case of lower laser-powers up to ca. 5 kW. The employment of ZnSe with higher laser powers leeds to an increasing danger of self-combustion (Selbstentzündung) of the lens due to the amount of laser-energy absorbed by the ZnSe-material.And: The combustion-products of ZnSe are harmful ! (note: Here glass as lens-material is not possible due to the CO2-lasers wavelength.) Therefore, in case of higher laser-powers (> 5 kW) mirror-optics are in use for the focussing of CO2laser-beams (mostly parabolic-mirrors).
Beam-Guidance to the workpieces via free-propagation:
Wich benefits are resultig from a short beam-path (<2m)
.
The short path between laser-resonator and focussing-lens is beneficial in several ways:
•Divergences Omega0 of the raw beams don´t lead (along the short path) to unwished changes of their diameters.
•No (or rare) optical elements for the beam-guidance (e.g. mirrors), thus low dangers through dust etc.
•To maintain laser-safety only short metallic tubes around the beam-path are necessary.
•Misalignment-dangers (Dejustiergefahren) between laser and lens are low (intercept-theorem [Strahlensatz] with short lengths! ). Therefore justifiable (vertretbar) low mechanical complexity (Aufwand) for a stable and rigid beam-guidance.
How are laser beams transported over longer (>2m) distances ?
Distinguish between the different types of lasers.
Beams of YAG- or Diode-lasers would be guided on longer paths via light-conducting-cables.
In the case of longer beam-paths between laser and workpiece, a beam-guidance via free-propagation is only used with CO2-lasers.
Wich spechial complexities has to be mentioned in case of longer beam-guidance via free propergation (using a high power CO2-laser) ?
- Limiting the divergence of the raw beam via Telescopes
- Constant-keeping (Konstanthaltung) of the raw beam´s diameter D and its divergence at the location of the focussing-element (am Ort des fokussierenden Elementes) via a “BeamTrombone”(“Strahlposaune”)
- Measures against dangers of dirt and misalignment
Name the main benefits of using light-conducting-cables (fiber-cabels)
- No danger of dirt-pollution along the beam´s path
- Laser-safety is reached simply: The cable has a plastic covering (wrapping), that can be checked against its through-melting via integrated electrical signal-wires
- No misalignment-dangers: The cables are flexible and follow all movements
Why are there bending restrictions for light conducting cables and how are these restrictions technicaly achieved?
Bending restriction: for guiding a beam through a LLK total reflection on the casing is required. If the bending radius passes a certain limit, total reflection is not longer possible.
Bending Radius limitations: for this purpose „bending-radiuslimiters“are part of the outer shielding-covers of the LLK (e.g. Kevlar-fibers).
Wich angle is crucial for incouppling a laser beam into a light conducting cable?
angle of aperture
Wich two different types of light conducting cables are relevant for materials processing ?
Wich one is the most important one?
1. Step Index Fibrer --> (most important one)
2. Gradient Index Fiber
Wich reasons for unsing a monitoring device can you think of?
- During the programming of the machinery along the edges of a workpiece (control)
- During the laser-materials-processing: e.g. observing the luminous-effects (Leuchterscheinungen) of the processing and the comparison of those observed during successful processings. Often used as quality-proofs during processes with quality-documenting-obligations.
Describe the principle setup of a laser guidance unsing a LLK.
.
How can you calculate the focus diameter of a laser beam after leaving a LLK?
-
How is a high beam-quality defined?
Which benefits reslt from a high beam-quality?
High beam-quality: long focus-length (Rayleigh-length)
Benefits:
- better accessibility to the workpiece (e.g. entering into a bore-hole)
- advantageous for ar„emote-beamguidance“(„Remote-Strahlführung)
Special Optics:
How can you achieve a twin focus?
.
Special optics:
Explain the functionality of 1- and 2-dimentional scanning optics
The beam ist guided via mirrors into the different directions.
Name one example for the use of 1-dimentional and and one examlpe for the use of 2-dimentional scanning optics.
1-dim.: Optics for laser hardening
2-dim.: Optics for "remote-laser-weldung"
