1. New high-power ultrafast laser and potential applications in biology and medicine Jeremy Allam Optoelectronic Devices and Materials Research Group Tel +44 (0)1483 876799 Fax +44 (0)1483 876781 University of Surrey School of Physics and Chemistry Guildford, Surrey GU2 7XH, UK

2. ultrashort pulses (5fs) broadband gain (700-1000nm) high power (TW) THz pulse generation 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)

3. Principles: System: Femtosecond high-power broadband source

4. Broadband sources for spectroscopy UVvisibleNIRMIRFIRMMWRF THz FEL Ultrafast electronics OPA Ti-S laser Ti-S SHG Ti-S THG DFMSFM HG-OPA

5. Ultrafast revolution

6. 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

7. Ablation with femtosecond lasers Conventional lasers (high average power) Femtosecond lasers (high peak, low av. power) dominated by thermal processes (burning, coagulation), and acoustic 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

8. Femtosecond vs. picosecond laser ablation deterministic -> predictable ablation stochastic -> uncontrolled ablation

9. Femtosecond interstroma Femtosecond LASIK Femtosecond laser surgery of cornea - 1

10. Femtosecond laser surgery of cornea - 2 Lenticle removal using Femtosecond LASIK

11. Imaging using femtosecond light pulses Nonlinear imaging for 3D sectioning (e.g. TPA fluorescence) scattering medium ballistic photons ‘snake’ photons diffusive photons time early photons Time-resolved imaging for scattering media femtosecond pulse detection region of TPA

12. Coherent control of chemical pathways Spectral-domain pulse shaping: Coherently-controlled multi-photon ionisation: