Continuum “White Light”
Generation
WhiteLase: High Power Ultra-
broadband Light Sources
Technology
Ultrafast Pulses + Fiber Laser + Non-linear PCF
= Spectral broadening from 400nm to 2500nm
Ultrafast Fiber Laser MOPA
• MOPA = Master Oscillator Power Amplifier
• All fiber design – no free-space optics
• In supercontinuum systems “post processing” is non-linear microstructured optical fiber (PCF)
Master Oscillator
• Diode pumped Yb fiber laser at 1064nm
• Passively mode-locked via saturable absorber mirror
• Self-starting operation providing transform limited pulses – 3ps (min) to >100ps (max)
• Repetition rate set by fiber length: – 20MHz (min) to ≈110MHz (max)
Changing Repetition Rate
5
•Repetition Rate
20MHz
•Pulse energy ≈100nJ
•Average Power 2W
•pulse-pulse: 50ns
•Repetition Rate
10MHz
•Pulse energy ≈100nJ
•Average Power 1W
•pulse-pulse: 100ns
•Repetition Rate
6.67MHz (custom)
•Pulse energy ≈100nJ
•Average Power
667mW
•pulse-pulse:150ns
•Repetition Rate
5MHz
•Pulse energy ≈100nJ
•Average Power
500mW
•pulse-pulse: 200ns
I
t
I
t
I
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PCF
t
Amplifier Pulse-
picker
Master
Oscillator
Supercontinuum Generation
• Spectrum related primarily to the Kerr and Raman non-linearities
• Raman scattering, Self Phase Modulation (SPM) and Four-wave mixing (FWM) involved
• Pump needs to be close to the zero-dispersion of the fiber in the anomalous regime
• High peak-power is maintained and the fiber non-linearity can be maintained over long interaction lengths
• Result is spectral broadening in both directions around the pump wavelength
Photonic Crystal Fiber (PCF)
• Microstructured fiber with solid silica
core and air/silica cladding
• High difference in refractive index
between core and cladding guides
light
– Single spatial mode at all wavelengths
– Small core-size enhances non-linear
effects
• Group Velocity Dispersion properties
can be carefully designed
7
Peak Power Drives Spectral Bandwidth
Peak Power Drives Spectral Bandwidth
Peak Power Drives Spectral Bandwidth
Peak Power Drives Spectral Bandwidth
Peak Power Drives Spectral Bandwidth
Peak Power Drives Spectral Bandwidth
Peak Power Drives Spectral Bandwidth
Peak Power Drives Spectral Bandwidth
Supercontinuum Laser Evolution
2005 2008 2010 2013 1W 6W >10W 4W
• Over the last 7 years, SC lasers have seen an order of magnitude
increase in their output powers.
• Market demands and technology developments are driving product
evolution in three key directions:
– Higher power
– More spectral bandwidth
– Lower cost / higher reliability
Higher Power Supercontinuum
• Spectrum is determined by the peak power of pump pulses.
• By increasing the repetition rate of the oscillator, the supercontinuum power
increases while the spectrum is fixed.
• Current state-of-art SC has >10W average power with >1.5W in the visible
range.
• Short term experiments (200h) performed at much higher powers of 30W
(5W visible power) have suggested significant power scaling is still
achievable using current technology...
10W laser
1.5W
visible
Limitations of Supercontinuum Lasers
• Photodarkening of fibers was historically a problem.
• Generation of deeper UV wavelengths inside fiber causes photodarkening.
• Proprietary fiber design can reduce photodarkening and enables SC systems capable
of operating at higher power levels and UV wavlengths…to a limited extent
• Further power scaling may involve combining multiple SC sources into a single high
power output of reduced “brightness”.
• Deeper UV wavelengths can be achieved by harmonically doubling SC output.
• Reliability of “youthful” technology.
Properties of Supercontinuum Light
• Broadband pulsed output
– Typically ≈2µm bandwidth
– Continuously bright spectrum with no “gaps”
• “Laser-like” beam propagation
– Collimated output
– Can be steered/manipulated like a laser
• Single spatial mode at all wavelengths
– Can be efficiently fiber-coupled
– Can be focused to diffraction-limited spot
– High brightness compared to other BB sources
• Ultrafast pulses at high repetition rate
– Can be used as Quasi-Continuous Wave source
– Can be used for lifetime study (≈50ps filtered pulse-width)
• Low temporal coherence – can be used for OCT
Applications
• Fluorescence excitation
• Industrial inspection and sorting
• Lifetime study
• Super-resolution techniques
• Medical illumination
• Broadband spectroscopy
• Nanophotonics
• Optical Coherence Tomography
• Hyper-spectral measurement
• Raman spectroscopy
• High intensity lamp replacement
Future Developments
• UV Supercontinuum – High Power <390nm
– Low Power <350nm
• Average Power Scaling – 10W supercontinuum released in 2012
– 30W supercontinuum demonstrated in lab
• Lower Repetition rates – Project to develop single-shot to 80MHz source
• Femtosecond Supercontinuum – Pumping PCF with femtosecond 1064nm laser source
Thank you
Tim Gerke
direct: 720-341-2784
Fianium WhiteLase
Compact mode-locked supercontinuum lasers
WhiteLase micro
ALP (Advanced Laser Platform)
WhiteLase SC400, SC450 & SC480
WhiteLase micro
• Spectrum from <450nm to >2000nm
• >200mW total output power (>20mW visible)
• 20MHz repetition rate
-40
-30
-20
-10
0
10
400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 2100 2200
Spectral power density (dBm/nm)
Wavelength (nm)
WhiteLase SC400 & SC450
0
1
2
3
4
5
6
7
300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 2100 2200 2300 2400 2500
Spectral Power Density (mW/nm)
Wavelength (nm)
SC400-6
SC400-4
SC400-2
WhiteLase SC450-HE
• Optimised for maximum supercontinuum pulse energy
• 1nJ/nm from 600-800nm
• Full Spectrum from <550nm to >1750nm
• Operates at 1MHz and 0.5MHz – user selectable
• Super-resolution and spectroscopy applications
0
1
2
3
400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 Spectral power desnity (nJ/nm)
Wavelength (nm)
SC390 UV-Enhanced
• Short-wavelength
cut-in <390nm –
shortest available
• Long wavelength
edge ~2400nm
• Up to 3W total
power
Acousto-Optic Tunable Filter
AOTF-DUAL
• Dual output filter module to cover extended wavelength range
• Can cover any two standard AOTF wavelength options
AOTF-HP
• New high-power version of Fianium AOTF system
• Provides >70% of supercontinuum power density to free-space unpolarised beam
AOTF • Removable tunable filter compatible
with all Fianium WhiteLase™ Supercontinuum Systems
• Up to 8 collinear individually tunable channels
• Three wavelength options covering full spectral range : 400-700nm, 650-1100nm & 1100-2000nm
SuperChrome™ Tunable Filter
Tunable Wavelength
• Single channel tunable from 400nm to 850nm
• Broadband “White Light” setting
Tunable Bandwidth
• <5nm to >50nm FWHM tunability
• Optimise channel bandwidth vs. output power
High Performance
• Up to 50dB out-of-band
suppression
• 80% transmission
• Fast 100nm/s tuning speed
• High beam quality
• Free-space or FC fiber delivered
output