New high-power ultrafast laser and potential applications in

biology and medicine

Jeremy AllamOptoelectronic Devices and Materials Research Group

Tel +44 (0)1483 876799Fax +44 (0)1483 876781

University of Surrey

School of Physics and Chemistry

Guildford, SurreyGU2 7XH, UK

ultrashort pulses (5fs)

broadband gain(700-1000nm)

high power(TW)

THz pulsegeneration

• pulse shaping• coherent control

parametric conversion

Why femtosecond lasers?

• timing physical processes

• time-of-flight resolution

generate: • UV• X-rays,• relativistic

electrons

1

2

3

(Titanium-sapphire properties)

CW DPSS pump

1-100 kHz rep. rate

TiS osc.

TiS CPA RGA

kHz DPSS pump

SP-OPO

HG

FM

OPA

WLG

HG

HG

700-1000nm350-500nm

550-800nm1.1-1.6µm

80MHz rep. rate

750-840nm1.1-3.0µm

3-10µm300nm-1.2µm

}}

Principles:

System:

AMPLIFICATION: regenerative chirped-pulse amplification

-> mJ pulses

LASER: self-phase modulation

in Ti Sapphire oscillator ->

<100fs pulses

CONTINUUM GENERATION: nonlinear processes

-> white light continuum

PARAMETRIC CONVERSION: white-light seeded

parametric amplification ->

broadband µJ pulses

Femtosecond high-power broadband source

Broadband sources for spectroscopyUV visible NIR MIR FIR MMW RF

THz

FEL Ultrafast electronics

OPA

Ti-S laser

Ti-S SHG

Ti-S THG

DFMSFMHG-OPA

Ultrafast revolution

electro-optic

samplingfree-space

THz

coherent control

NL pulse propagation

microwave photonics

ultrafast opto-electronics

biological / environ-mental

sensing

photo-chemistry

medical applications

material processing

non-linear optics

non-stochastic breakdown

optical spectro-scopy

high-energy physics

solid-state femtosecond

lasersintense (>1TW)

tunable (UV-MIR)

coherent

ultrashort (<10fs)

relativistic electron motion

high-harmonic

generation (UV, X-ray)

controllable ablation

THz device physics

Why femtosecond lasers in biology and medicine?

Conventional laser applications

imaging

Benefits by using femtosecond lasers

• wide spectral range• coherent control

ablation • more controllable• less damage

spectroscopy

• nonlinear imaging (e.g. TPA, THG)->3D optical sectioning-> contrast in transparent samples

• time-of-flight resolution: early photons in diffusive media

• THz imaging

Ablation with femtosecond lasersConventional lasers(high average power)

Femtosecond lasers(high peak, low av. power)

• dominated by thermal processes (burning, coagulation), andacoustic damage

• collateral damage(cut cauterised)

• absorption within illuminated region

• stochastic -> uncontrolled ablation

• dominated by non-thermal processes(‘photodisruption’)

• little collateral damage(cut bleeds)

• strong NL effects only at focus (-> sub-surface surgery)

• deterministic -> predictable ablation

* due to dynamics of photoionisation (by light field or by multi-photon absorption) and subsequent avalanche ionisation

Femtosecond vs. picosecond laser ablation

deterministic -> predictable ablation

stochastic -> uncontrolled ablation

Femtosecond interstroma

Femtosecond LASIK

Femtosecond laser surgery of cornea - 1

Femtosecond laser surgery of cornea - 2

Lenticle removal using Femtosecond LASIK

Imaging using femtosecond light pulsesNonlinear imaging for 3D sectioning(e.g. TPA fluorescence)

scattering medium

ballistic photons‘snake’ photons

diffusive photons

time

early

ph

oton

s

Time-resolved imaging for scattering media

femtosecond pulse

detection

region of TPA

amplitude & phase LCD mask

in out

Coherent control of chemical pathwaysSpectral-domain pulse shaping:

ener

gy

distance

Coherently-controlled multi-photon ionisation: