Laser Solutions Short Courses › pdf › SC5_Juergen...Tips and tricks – free space laser A beam...

Laser Solutions Short Courses

Short Course #5

Laser Beam Sources - Which Laser for Which Application

Juergen Stollhof Course Instructor

Thursday, November 5 8:20AM

Room: Narcissus/Orange

Laser beam Sources –Which Laser for Which Application?

Juergen StollhofTechnical Sales ManagerTRUMPF Inc. Plymouth, MI

Which laser for which application? ICALEO 2009 2

Content – a world of lightBeam sources for material processing

A tool of light

A world of possibilities

Summary


Pulsed Laser ParametersPulse Energy

E= Ppeak × t

Average Power

Pavg = E × f

Where:

f = repetition ratePpeak = pulse peak powert = pulse duration

Power

tPavg

Ppeak

E

1/fTime


What makes a beam good?

Beam quality is characterized using these measures.


CO2 Gas laserFlowing gas laser - Design- Gas flowing in quartz glass tubes- Electrodes at the outside of the

tubes energize the laser gas- Total discharge length: serveral

meters- Bending mirror, rear mirror and

output mirror define the resonator- Turbine blower in the center

circulates the gas- Continues gas flow while the

cooling coil controlling the gas temperature

- Vacuum pumps ensures constant pressure (about 100 hectopascals)

Compact, powerful, and reliable: a glimpse inside a flowing gas CO2 laser with square design


CO2 Gas laser – Diffusion cooled

Resonator is based on two metal tubes, which functions as RF electrodes

Discharged path between these tubes

Beam circulates between helix mirror and Axcon mirror

Output window in the helix mirror

The medium power specialist: a glimpse inside a diffusion-cooled CO2 laser


Rod laser Disk laser

r

T

r

T

Pump lightQuasi frontal

Cooling throughground surface

Parabolic temperature profile Flat temperature profile

Laser emission

Fiber laser

- +

Diode laser

Cooling and Pumpingthrough lateral surface

Direct conversionof el. current in light

Cooling throughlateral surface

Currently used solid-state laser concepts


Light from crystals and glass

Nd: YAG- Light from arc lamp or diode laser

dumping the 4-level-laser- Crystal: yttrium aluminum garnet- Doped crstyal: Neodymium

concentration in the range of 1 %

Yb: YAG or Yb:glass- Disk laser or fiber laser- Crystal: yttrium aluminum garnet or

glass- Doped crystal: Ytterbium

concentration in the range of 10 % Doped crystal: ions of another element, or “foreign” ions, are incorporated into the crystal lattice, which is called the host lattice.


Mother of all beam sources: the rod laserLamp pumped- Rod geometry: about 5 mm

diameter and max. 20 long- Arc lamp located at each

side of the rod- The double ellipse cross

section of the cavity reflects the light into the rod.

Diode pumped- Laser diodes emitter laser

light around 808 nm, optimized for absorption in the rod

Limited by thermal lens

A laser classic: a glimpse inside a rod laser


Fiber laser – a concept with potential

All-in-one design: a glimpse inside a fiber laser


Fiber laser – a concept with potentialAll-in-one-designPump light must be fed into the pump fiberRear and output mirror integrated into the fiber core: Bragg grating generated by alternating high and low refraction indices


Rod laser Disk laser

r

T

r

T

Pump light-radial

Pumplight-frontal

Cooling through back side of the disk

flat temperature profile due to 1D- heat conduction!

Laser emission

coolingradial

parabolic temperature profile due to2D- heat conduction


TLS Disk - Cavity

Pumping a Disk Laser


1

Pump-Reflector

Disk withRear Mirror

Pump- Cavity

1

2

34

58

6

7

Prism Pair

Parabolic Mirror

Outcoupler

Laser beam

Pump- Beam

1

Pumping of a Disk

Actually: 20 passes of the pump light through the disk!


TruDisk

5

4

3

2

1 Pump unit

Cavity

Laser resonator

Power feedback sensor

Central shutter

1

2

3

4

5


Inversion and photon emission

Offset of the energy band due to different composition of the semiconductor

External voltage arranges the bands and injects electrons and positive holes into the pn-junction

InversionEmission of photons E

E


HR

Outputcoupler

Beam

Diode laser


Beam characteristic of single emitterPerpendicular to pn-junction (fast axis)

Almost diffraction limitedHeight of emission: 0.5 ...2 μmDivergence: 40..70°BPP: ~ 0.3 mm mrad

Parallel to pn-junction (slow axis)Multi-modeWidth of emission: ca. 60..200μm Divergence: 6..12°BPP: ~ 5 mm mrad


Laser diode barLateral design of optical independent emitters

Overlap of the emitted light is incoherent Asymmetrical beam characteristic - Fast Axis: 0.3 mm mrad (fundamental mode)- Slow Axis: 350 mm mrad (complete bar)


Diode stacks

Single EmitterSingle-mode: about 1 WBroad Area: up to 15 W

BarsSeveral broad area emittersAbout 100 W

StacksStacking of barsIn the range of 1000 W


LU 22

P2BPP2

LU 11

P1BPP1

Wavelengthcoupling

1+ 2P=P1+P2= ~3000 W ex 600 μmBPP=BPP1=BPP2

Power Scaling for TruDiode 3006

3 kW ex LLK06

2 Laser Units

2 Wavelengths


TruDiode with Beam Management

Laser device includesbeam management components for up to 6 fiber outputs


From Source to workpiece

The laser beam of a CO2 laser is usually expanded, routed through tubes or bellows, and finally focused with mirrors or lenses.

The laser beam of a solid-state laser is usually routed to the workstation in a fiber optic laser cable and focused using lens systems.


Tips and tricks – free space laser

A beam telescope Adaptive mirrors

A beam telescope is used to enlarge the diameter of the laser beam, so that divergence is reduced and the beam can be guided more easily.

The adaptive mirror is curved outward by water pressure to control the divergence angle of the laser beam on the focusing lens.


Beam in a cable

Total internal reflection: laser light zigzags through a step-index fiber

Fibers and laser light cable


Focus and focusing lenses

A shorter focal length (left) produces a smaller focus diameter with shorter image distance, shorter Rayleigh length, and less depth of field.


High beam quality means

Higher beam quality enables - a smaller focus diameter with the same focal length (left), - a greater standoff with the same focus diameter (center), - a smaller beam diameter on the lens (right),- bigger scanning field (not shown)


Focusing properties

Collimation Lens

Observation

f

dk

fc

dof

dof =ffc

. dkf

A =fc

mirror

dk

fc

dof

f

A

Focus diameter

Focal length of the lens

Focal length of the collimation

Core diameter of the laser light cable

Optical ratio


Optics: more than mirrors and lensesTasks of a processing optic

Supply the auxiliary materials: gas for cutting or welding or filler materials for weldingSensores for process controlProviding interfaces for the machine (for example power connections, collingwater, data interfaces)Protection glasses or crossjetsPower meters and pilot light

Welding optics for solid-state lasers


Scanning optics: Focusing plus movement

The scanning principle: two rotating mirrors deflect the laser beam.

Scanning optics for solid-state lasers: a flat field lens focuses the laser beam, producing a flat, elliptical working field.


PolarizationGood vibrations- Unpolarized: Light waves oscillates randomly in different directions- Linearly polarized light: All waves oscillate in the same direction- Circularly polarized light: The direction of oscillation rotates

Linearly polarized light (top) and circularly polarized light (bottom)


Conversion principle

Wavelength can be changed by guiding the laser beam through a crystal with nonlinear propertiesLight strikes a crystal electron shells begin vibrate (harmonically)Laser beam high intensity electron shells begin to vibrate not only harmonically but also with higher harmonics (second, third,…)

In goes infrared, out comes green: nonlinear crystals change the frequency and, thus, the wavelength of the laser light.


A world of possibilities – laser applicationsLaser meets workpiece

Welding

Cutting

Drilling

Structuring and ablation (including marking)


The optimum machining process

Heated materialMolten materialVapor

--- Ejected material

Vaporizationand ionization

Sublimationand direct dissociation

10 GW / mm²

ps

Structuring

10 MW / mm²

ns

Ablation,engraving

Vaporization

1 MW / mm²

ms

Drilling

Melting

1 kW / mm²

ms

Heatconduction welding

Main effect Heating Melting and vaporization

Power density starting from

30 W / mm² 10 kW / mm²

Interaction time s ms

Process examples Hardening,soldering

Deeppenetrationwelding,cutting

Power density and interaction time determine how much energy is delivered to the workpiece and what the resulting effects will be. Shown here: metals.


Laser meets workpiece

The laser unit is part of an interconnected whole. The properties of its components determine the machining parameter settings.


Laser Welding - Types of lasers

Fiber deliverable(1 micron, solid state laser)

Hard optics(10 micron, gas laser)

Nd:YAGNeodymium: Yttrium Aluminum Garnet

Lamp pumped rod

Yb:YAGYtterbium:

Yttrium Aluminum GarnetDiode pumped disk

CO2Carbon dioxide

RF excited

Pulsed20-550 W

CW380-4,400 W

CW1,000-16,000 W

FAF700-20,000 W

COAX1,000/2,000 W

Yb:QuartzYtterbium: Quartz

Diode pumped fiber

CW200-400 W

DiodeDirect diode

CWup to 3,000 W


Heat conduction weldingDescriptionHeating the workpiece above the melting temperature without vaporizing

CharacteristicsLow welding depth (~2mm max)Small aspect ratio (i.e. wide weld)Low coupling efficiencyVery smooth, highly aesthetic weld bead

ApplicationsLaser welding of thin workpieces like foils,wires, thin tubes, enclosures, etc.

vS

Laser beam

Processing gas

Welding seam Work-piecetS Melt


Keyhole weldingDescriptionHeating of the workpiece above the vaporization temperature and forming of a keyhole

CharacteristicsHigh welding depthHigh aspect ratioHigh coupling efficiency

Smaller HAZ, plasma supp more critical (CO2 & high P fiber), difficult on thin materials (<0.75mm)

vS

Laser beam

Processing gas

Laser-inducedplasma

Welding seam Melt Work-piece

Keyhole

tS


Coupling efficiency

Coupling efficiency is dependent on …

Laser type (wavelength)Material reflectivity / thermal conductivityMaterial quality / cleanlinessWeld joint geometryPlasma suppressionPower density

Key-Hole Weldinghigh absorption, deep weld, smaller HAZ, plasmasuppression

Thermal ConductionWeldinghigh reflection,shallow flat smooth weld, larger HAZ, no plasma

Power Density (W/cm2)

Weld

Depth

(mm)

Thre

shol

dIn

tens

ity

plasmashielding

Key-Hole Weldinghigh absorption, deep weld, smaller HAZ, plasmasuppression

Thermal ConductionWeldinghigh reflection,shallow flat smooth weld, larger HAZ, no plasma

Power Density (W/cm2)

Weld

Depth

(mm)

Thre

shol

dIn

tens

ity

plasmashielding


Inter-relationships

If the focal length “f” is doubled, then …

a. “d” increases by a factor of 2

b. “L” increases by a factor of 4

c. “Pd” decreases by a factor of 4

f1

d1 d2

L1 L2

D1 = D2

f2


Pulsed laser weldingTypical applications:hermetic welding, pseudo continuous welding and spot welding.

Key parameters …1. Pulse energy (Ep = Pp x t)2. Peak power (Pp = Ep / t)3. Average power (Pave = Ep x )4. Hermetic requirements, %OL

( = 5V/dw) for 80% overlap

Power

tPavg

Ppeak

E

1/ Time


Weld Geometry & BPP/Power Density

TruFlow 6000

P = 5700 W at workpiece

V = 2.3 m/min

M2 = 1.8 (approx. Gaussian)

TruFlow 6000


V = 2.3 m/min

M2 = 3

TruFlow 8000 (high order mode)


V = 2.3 m/min

M2 = 7.7 (approx. top hat)

What’s the disadvantage?

1. Need excellent part fit-up and seam location for butt weld

2. Small weld width at interface for overlap weld

What’s the disadvantage?

1. Slower for a given weld penetration

2. Larger HAZ and distortion


Seam and joint types

Name

Seam weld on butt joint

Lap weld on lap joint

Example Characteristics

+ weld fusion area(less material, weight & cost savings)Also: faster or less power, no issues w/Zn, no step

- positioning tolerance(edge requirements, fit up can bemore difficult to obtain)

+ positioning tolerance(larger process window)

- weld fusion area(more energy required = slower or higher power, more distortion/HAZ)


Schweißen mit TruDisk 8002, TruDisk 6002, TruDisk 4002

0

5

10

15

20

25

0 2 4 6 8 10 12 14

Einschweißtiefe in mm

Schw

eißg

esch

win

digk

eit i

n m

/min

P = 8 kWP = 6 kWP = 4 kW

Werkstoff : Baustahl Fokussieroptik: PFO33Fokusdurchmesser: 0,6 mm

TLS259oy05.03.2007

Welding with cw DPSSL -TruDisk 4002, 6002 and 8002

Wel

ding

Spe

ed[m

/min

]

Welding depth [mm]

Material: Mild steelFocusing head: PFO 33Focus diameter: 0,6 mm


Laser Cutting - How it worksFocused beam strikes the workpieceMaterial starts to meltLaser beam pierce the workpieceLaser beam moves along the part contourJet of gas is usually used to blow out the melt


Principle of laser cuttingProcess steps

AbsorbingHeatingMelting and evaporatingStart of cutting process after complete penetrationAssist gas to blow out the molten material


Cutting criteria: Quality

1 Spatter

2 Blowout

3 Striation

4 Erosion

5 Burr / dross

6 Perpendicularity


Cutting with TruFiber 300

Speed limited by machine: 60 m/min


Comparison YAG – CO2 Nitrogen cutting (metals)

SSL CO2

Very thin material thickness, Foil < 1mm

extremely good results good result

Thin material thickness1 – 3 mm

very good results very good results

Medium material thickness3 – 6 mm

limited results very good results

Thick material> 6 mm

poor results good result

Simplified view for N2 cutting


Sublimation Cutting of Metal

No significant melt or debris

No measurable Heat Affected Zone

Materials (i.e.):• Stainless Steel• Nitinol• Copper• ….


How it worksFocused beam melts and vaporizd he materialVapor pressure expels the molten materialMolten and vapor shoot upwards to the opticsOnce the beam breaks through: spatter and vapor exit through the bottom

How laser drilling works: the laser melts and vaporizes the material. The vapor pressure expels the molten material from the hole.


Drilling strategiesSingle-shot drilling:

Single laser pulse, high pulse energyLarge number of holes can be created in an extremely short time

Percussion drilling:Multiple short-duration, low-energy laser pulsesdeeper, more precise holes than single-shot drillingSmaller holediameters

Trepanning drilling:Multiple laser pulsesPilot hole is first created using percussion drillingLaser enlarges pilot hole, moving in increasing larger circlesMaterial is expelled downward

Helical drilling:No creation of pilot hole, laser moves in circles as the pulses are deliveredLaser works its way in a downward spiralMaterial shoots upward


What distinguishes a good hole?Dimension and tolerancesTaperMaterial depositsEdge quality and burr formationEffect (HAZ) on the workpiece

Factors used in determining the quality of the hole. Cool air flows out of film-cooling holes and over the turbine blades.


Influence of Pulse Duration on Quality

Pulse Duration

meltdebris

nonlineareffects

precisionQua

lity


Automotive: Drilling with high Aspect RatioHelical Drilling of Stainless Steel

No melt or debris

No Heat Affected Zone

Free selection of taper (positive, negative or zero)

Diameters: 50 to 100 μm

Material thickness: up to 1.5 mm

Applications: Injectors


Automotive: Drilling with high Aspect RatioHelical Drilling of Stainless Steel

No melt or debris

No Heat Affected Zone

Free selection of taper (positive, negative or zero)

Diameters: 50 to 100 μm

Material thickness: up to 1.5 mm

Applications: Injectors


Drilling on the fly of Green Ceramic FoilsDrilling on the fly (percussion)

Diameter < 100 μm

Drilling rate: > 800-1000 holes/sec

Negligible melting of Mylar tape on backside


Efficiencyof theablation process

Ablation threshold decreasing with pulse duration

Ablation rate per pulse increases with pulse energy

Higher efficiencyshorter pulse duration increased pulse energy increased frequency Higher average power


Economical point of view

Average power [W]

Pulse length [s]10-15 10-12 10-9

Q-switch,cavity

dumping,MOPA

Mode locking

LZH

CPA

ns regimeps regimefs regime

1

10

100

FU Berlin


PV: Laser Border Deletion – TruMicro 7050Removal rates increased by quadratic fibersAblation rate up to 50 cm²/s – through glassHigh transmission through delaminated areaInsulating resistance > 100 M


PV: Thin Film AblationLaser patterning of thin TCO on CIGS

Advantages:- Burr free- Melt free- No delamination- High speed (> 1,2 m/s)

Application: P3 step for CIGS cell connection


PV: Thin Film AblationLaser patterning of thin films on Silicon

Direct patterning of SiO/SiN layers

Thickness of layers: 100 nm

Single shot ablation

Selective removal without affectingbase material (Silicon)

Application: Cell connection for Silicon Solar Cells, low-k dielectric grooving


Semicon: Scribing of CeramicsAdvantages:

Small kerf width (< 20 μm)

Negligible HAZ

High quality of cutting edge

High productivity due to high average power

Applications: Scribing / cutting of ceramic PCBs


SummaryImportant parameters

WavelengthPulse duration (application process time)Beam quality (focusibility)Technical realization (stability of the process)Economical aspects


Disk / Fiber

Diode DPSS

Beam quality

BP

P [m

m m

rad]

Output power [kW]

TruDiskProducts 2009

5

10

15

20

25

June 2008: Boeing27 kWnearly diffraction limited

5 10 15 20 25 30


Absorption rate (at 20°C)

0

20

40

60

80

100

0,1 1 10Wavelength in µm

Abs

orpt

ion

in % Glass

FeAl

Ag

Cu

CO2=10,6 µm

Yb:YAG=1,030 µm

Diode~ 900 µm

IRUV

30,3

Yb:YAG=515 µm

Yb:YAG=343 µm

Yb:YAG=258 µm


Types of Applications

structuring

marking

Pulse duration in s

Pow

er d

ensi

tyin

W/c

m²

107

110-310-610-9

cutting

drilling

1 kJ/mm²1 J/mm²

Absorb. Energiedichte: 10 mJ/mm²

106

105

104

108engraving

welding

heat treatment


Parameters

WavelengthWavelengthPeak powerPeak powerPulsePulse lengthlengthBeamBeam qualityquality

feasibilityfeasibility

HighHigh frquencyfrquency ororcw mode cw mode

aveave. power. power

economicaleconomical

stabilitystability......

......fromfrom pulse to pulse.pulse to pulse.…… beambeam qualityquality

RepeatabilityRepeatability

And now I look forward to your questions!

Juergen StollhofTRUMPF Inc.Laser technology Center 47711 Clipper StreetPlymouth Township, MI [email protected]

ICALEO® 2009 Laser Solutions Short Course Evaluation

Course #5: Laser Beam Sources - Which Laser for Which Application Course Instructor: Juergen Stollhof Please rate the following: (circle) Very Course Excellent Good Good Fair Poor Overall Course 5 4 3 2 1 Course Instructor 5 4 3 2 1 Presentation of material 5 4 3 2 1 Organization of material 5 4 3 2 1 Course well paced 5 4 3 2 1 Would you recommend this course to others in your profession? yes no

What was the strongest feature of the course? What was not covered that you felt should have been covered (if anything)? What would you like to hear more about next time? What was covered that left an impression/impact on you? Suggestions & Comments (for this course or courses you would like in the future): Name: (optional)

Please Use Reverse Side for Additional Comments.

Please return evaluation form to the Registration Desk by Thursday afternoon

or fax 407.380.5588 to LIA upon your return home.

THANK YOU!

Laser Solutions Short Courses › pdf › SC5_Juergen...Tips and tricks – free space laser A beam...

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