Introduction to NanoScan - Laser Optics - Ophir Laser ... · • Laser and LED manufacturers –R & D and production –Production test laser manufacturing paraxial sources • Fiber

Introduction to NanoScan

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Introduction to NanoScan

• How does it work?

• What is a slit profiler good for?

• How does it differ from a CCD?

• Who wants one?

• Why do they want it?

• How do you sell it and to whom?

3

NanoScan

How does it work?

4

Beam Sampling Technique

5

Beam Sampling Technique

6

Slit Scanner Operation

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What is it good for?

• In general, NanoScan

is used for focused or

collimated beams

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Beam Width, Clip Level Method

Irra

dia

nce

Distance Across Beam

100%

13.5% (1/e2)

Irradiance = Power/unit area

FWHM

Laser Beam Profile

Centroid

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4-Sigma Measurement

4-sigma measurement points

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NanoScan d4 2nd Moment Calculation

Slit Scanner Output Profile

Profile for narrow slit

2nd Moment from slit profile

Discrete sum in practice

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Ellipticity

DX

DY

E = DX

DY

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NanoScan Configurations

• Silicon Detector

– 190-900nm

• Germanium Detector

– 700-1800nm

• Pyroelectric detector

– 200nm->>20μm

Measures most Wavelengths

13

Available NanoScan Scan Heads

• Silicon Detector (visible λ)

– λ =190 to 900 nm

• Not recommended for >1000nm

– 10 μm to 20 mm spot size range

• Germanium Detector (near IR λ)

– λ =700 to 1800 nm


• Pyroelectric Detector

– λ =0.25 to 20 μm including 10.6 μm



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• Standard Head has 2 Apertures—3.5mm, 9mm

– 3.5 mm Aperture has 1.8μm Slit Size

– 9 mm Aperture has 2 Slits

• 5μm and 25μm

• Large Aperture Heads

– 25mm for Si, 20mm for Pyro, 12mm for Ge

– Slits 25μm

Measures very small beams

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How small a beam can be measured?

• Selection of slit width:

– 1/4 or less than 1/e2 beam width

• Selection of aperture size; e.g.

– 3.5mm –1.8µm slit

– 9mm—5µm or 25µm slits

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Convolution Error

• Due to the Convolution Effect, slit width

should be smaller than 25% of the 1/e2 width

of beam.

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NanoScan Operating Space Advantage

Has very large dynamic range

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Advantages of Dynamic Range

• Measures focus and defocused beam

• Measures most beams without attenuation

• No need for adjustments to beam or

attenuation during measurements

• Excellent for M2 Measurements

– Makes NanoModeScan fast

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Slit Plane is

Measurement Plane

Measures Beam Directly

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Slit Plane Well-defined

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Advantages of Known Slit Plane

• Measures tightly focused Beams

• Finds beam waist locations to high precision

• Reproducible measurements

• Guarantees optical system performance

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Pointing Accuracy

• Very low jitter

• Pointing precision to ~50nm

• Guarantees consistent performance

• Accurate pointing measurement in small space

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Other Capabilities-Multiple Beam Analysis

• Up to 16 Beams

• Measures individual

parameters

• Linear arrays only

• Operate at 45°Use

Rotation

transformation in

software

– Analysis window

– Enter 45°

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Rotational transformation

• Changes the coordinates

from default

• Report separation as

linear

• Operation at 45°

precludes elliptical

analysis

• Beams will be assumed to

be round

• Use for alignment, not

detailed structure analysis

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ROI Selection

• Up to 16 ROIs

• Color coded for display

of individual beam data

• Automatic or manual

selection

– Drag and drop

– Numerical input to dialog

box

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What Doesn’t it Do?

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2-D/3-D Image is only an approximation

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Real 2D/3D is for Cameras

Customers who want a

real 2-D image of their

beam should get a

camera.

NanoScan is for

measuring beam width of

generally Gaussian or

semi Gaussian beams

NanoScan is not good for

higher order beam types

NanoScan does not

measure flat-top beams

well

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Slow Pulsed Beams

• NanoScan measures beams >5kHz rep rate

• Use Cameras for slower repetition rates.

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Measuring Pulsed Beams with the

NanoScan Slit Profiler

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What Sort of Pulsed Beams can be measured?

• Must be 5kHz and above repetition rate

• Must be stable

– Rep Rate

– Power per pulse

• Energy per pulse must not exceed Damage

thresholds

• Average power must be in operating space

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Types of Pulsed Beams

• Pulse Width Modulated (PWM)Lasers

– Power control

– Common in CO2 Lasers

• Q-Switched Lasers

– Method of increasing effective power

– Short pulses

• Pico- and Femtosecond Lasers

– Lower average power

– Very high peak powers

– Energy per Pulse (Epulse) important parameter

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Pulsed Beams

• CO2 Pulse Width

Modulation @ 50%

• Picket Fence

• 10kHz Rep Rate

• Pulse Mode Off

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Pulsed Beams

• PWM @ 95%

• Typical Power control

for CO2 lasers

• User often thinks it’s

CW, or

• User does not know

the rep frequency

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Pulsed Mode On

• Peak Connect algorithm

• Finds Peaks

• Uses Repetition

Frequency to draw peak

• Must have the right

Frequency

• NanoScan measures

Frequency

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Repetition Frequency vs Beam Size

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Pulsed Beam Complications

• Pulse Width Modulation

– Treat like CW for Power calculations

– Use Average Power

• Q-Switched and other energy increasers

– For pulse durations <10-6 second (<1μsec) or

shorter

– Calculate Energy per pulse

– Use the Slit Damage Calculator

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Problematic Pulsed Beams

• Lasers with uneven power per pulse

– Peak connect can find beam top

– Unstable profile

• Lasers with too low pulse rate for beam size

– Camera may be necessary

• Femtosecond Lasers

– Can have very high peak powers

– Non linear effects on slit material

– Not well understood at this time

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Pulse Effects on Power

• Epulse goes down as

frequency increases

• Ppulse increases as

pulse duration

decreases

• This can be dramatic

as durations approach

10-12 (ps) or 10-15

(fs)

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Measuring fsec and psec Lasers

• Determine the Energy per pulse

laser

avg

pulsef

PE

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Measuring psec and fsec Lasers

• Calculate Energy Density per pulse for 100μm

Beam:

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Damage Thresholds

• 5J/cm2—Cu Slits at >3μm

• 2.5J/cm2—Cu Slits 700nm-3μm

• 1J/cm2—Ni Slits at >400nm

• 600mJ/cm2—Ni Slits at 190nm-400nm

• 10mJ/cm2—Blackened slit material

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NanoScan Heads for fsec Lasers

• Use Average Power to Select Detector

• Use Epulse to determine aperture type

• Use Unblackened Slits and Drums

• High frequency (>100kHz) lasers can be

measured in CW mode with filtering

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Potential Issues of Short Pulses

• Changing Frequency alters Energy

• The lower the frequency, the higher the Energy

per Pulse

• Can exceed the damage thresholds

• Use the Calculator

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Slit Damage Calculator

Slit WL Range Diameter(um)Avg Pwr(W)Freq(kHz) Pulse Width (nsec) Energy(J) Power Density(W/cm^2) Energy density (J/cm^2) Peak Irradiance (W/cm^2)Cu >3um 1000 500 5 50 1.00E-01 6.37E+04 1.27E+01 4.00E+06

Cu 700nm-3um 75 50 cw NA NA 1.13E+06 NA NA

Ni/Cu 190-400nm 20 1 10 100 1.00E-04 3.18E+05 3.18E+01 2.00E+03

Ni >400nm 80 0.5 50 0.1 1.00E-05 9.95E+03 1.99E-01 2.00E+05

Ni Blk 190-700nm 75 0.001 10 0.0001 0.0000001 2.26E+01 2.26E-03 2.00E+06

Ni Blk 700nm>3um 1000 0.1 cw na NA 1.27E+01 NA NA

6

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Four Key Questions for Selecting a Profiler

• What wavelength is the light?

• What is the spot size? How is it defined?

• What is the beam power?

• Is the beam pulsed or continuous

wave (CW)?

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What Wavelength is the Light?

• Determines the detector

– Silicon 190 - 1000 nm

– Germanium 700 - 1800 nm

– Pyroelectric 200nm – 20+ µm

(high power)

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What is the Beam Width?

• Selection of slit width:

– 1/4 or less than 1/e2 beam width

• Selection of aperture size; e.g.

– NanoScan 3.5mm

– 9mm

– Large Aperture

• Si—25mm

• Ge—12mm

• Pyro—20mm

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Convolution Error

• Due to the Convolution Effect, slit width

should be smaller than 25% of the 1/e2 width

of beam.

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What is the Beam Power?

• Check the Operating Space Charts

• Make sure the beam won’t damage the

scanhead or slits

• Is the pyroelectric detector the best option?

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Is the laser CW or pulsed?

• If CW, All OK

• Is frequency high enough?

– >1kHz

– Fast enough for the beam size

• >100kHz treat like CW

–

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How do NanoScan Applications differ from

CCD Apps? • NanoScan gives real time feedback

– No in-test adjustments necessary

– Direct, often optics-free, measurements

• Used for Processes

– Focusing lasers

– Adjusting optics

– Collimation

– Aligning Optics

• All in Real Time

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NanoScan Customers are

usually working on a Process

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NanoScan Applications

• Usually simple result required

– Beam Size

– Beam Position

– Divergence

• Not looking for complex beam shapes

• Use is not unlike a power meter

– Instant feedback

– Measure while adjusting

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NanoScan Markets & Applications

• Laser Printers

– R & D product development

– Component inspection; sub-assembly

– Final scan lens test

– LD collimators

• Bar Code Scanners

– Component sub-assembly

– LD collimators sub-assembly

• Optical Memory

– Mostly R & D

– LD collimators sub-assembly

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• Laser and LED manufacturers

– R & D and production

– Production test laser manufacturing paraxial

sources

• Fiber optic passive component manufacturers

– GRIN lens collimation

– Coupling LD to fiber

– Test of diffractive optic lens

– NA of fiber

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• Laser optical system builders

– Component test

– Sub-assembly

– Final test

– Verification in installed systems

– Assist source replacement in field

• Medical laser optical systems

– Final test

– Component test

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Who buys NanoScan?

• Industrial Customers who want:

– Ease of use

– Speed

– Reproducible results

– Accuracy of Measurement

• Minimal optics

• Minimal variables in set up

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Who buys NanoScan?

• Research customers who:

– Need to measure small beams

– Want to measure high power beams with minimal

attenuation.

– Have complex optical systems

– Work in IR wavelengths where NanoScan is less

expensive alternative

– Have multiple laser systems to measure

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Who buys NanoScan?

• Laser manufactures who want:

– To match users’ measurement techniques

– Speed of measurement

– Reproducible results

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Who buys NanoScan?

• Customers who need:

– Pointing accuracy

• Laser printer

• Military sighting and rangefinding

• Marking machines

– Collimation

– Cost-effective IR applications

– Small beam applications

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Contact us for a demo

Documents

Introduction to NanoScan - Laser Optics - Ophir Laser ... · • Laser and LED manufacturers –R & D and production –Production test laser manufacturing paraxial sources • Fiber