1. TOWARD GENERATION OF HIGH POWER ULTRAFAST WHITE LIGHT LASER USING FEMTOSECOND TERAWATT LASER IN A GAS-FILLED HOLLOW-CORE FIBER
Walid Tawfik
Physics and Astronomy, King Saud university, Riyadh, Saudi Arabia.
Department of Environmental Applications, National Institute of Laser NILES, Cairo University, Cairo, Egypt.

2. King Saud University

3. Dr J P Singh Tayyab Imran Visiting Professor from
Mississippi State University 

4. Outlines
Why we need white light (tunable) high-power few-cycle laser pulse?
Experimental setup layout.
Output characteristics.
Using SPIDER for measurement of few-cycle pulses
Controlling the Tunable broad-bandwidth ultrafast laser pulses.
Conclusion.

5. The ultrafast progress has been amazing!
YEAR
Nd:glass
S-P Dye
Dye
CW Dye
Nd:YAG
Diode
Nd:YLF
Cr:YAG
Cr:LiS(C)AF
Er:fiber
Cr:forsterite
Ti:sapphire CP M
w/Compression
Color
Center
1970
2015
SHORTEST PULSE DURATION
10ps
1ps
100fs
10fs
2020
Nd:fiber
10 As
The shortest pulse vs. year (for different media)
Erich Ippen,
MIT

6. Why try to make ultrafast pulses?
Bohr-orbit time in hydrog 152 attoseconds
Molecular vibrations can also be very fast.
H2 vibrational oscillation period: ~ 7 fs

7. Transient Absorption – in complex System
Vibrational Relaxation (VR), Intersystem Crossing (ISC), and Internal Conversion (IC)
Aspects of VR
Pump wavelength dependence
Density of states
Probe wavelength dependence
Franck-Condon Factors
Full-spectrum, Kinetic trace
Needed Information
Steady State absorption and emission
geometry
Electron configuration
Pump Photons create the excited state in a given vibrational state. Probe photons are absorbed by the excited state. The difference in intensity between the incident and transmitted probe photons gives the measured signal. The transmitted intensity changes as the excited state population in the S1 state decays. Possible decay processes.
Changing Pump Wavelength places the S1 state in a different vibrational level. Higher in the vibrational manifold, there is a higher density of states due to anharmonicity. Increases the Franck-Condon overlap and facilitates vibrational decay.
Probe Wavelength: Higher vibrational states have a wider range of absorptions available due to greater franck-condon overlap with a larger number of vibrational states in the upper level. There are many more nodes in the highly excited vibrational wavefunction and more amplitude over the nuclear coordinate.
Reference: Cr(acac) paper.

8. Pulse energy vs. Repetition rate
Regen + multipass
10-9
10-6
100
10-3
Regen
1 W average power
Pulse energy (J)
Regen + multi-multi-pass
RegA
Cavity-dumped oscillator
Oscillator
109
106
103
100
10-3
Rep rate (pps)

9. Short pulse oscillator
The Amplification of Ultra- short Laser Pulses using Chirped pulse amplification (CPA)
Short pulse oscillator t
Dispersive delay line t
Solid state amplifier t
Pulse compressor t

10. Schematic diagram of the few-cycle white light generator.
The experimental setup for the project, where the laser system provides 35-fs pulses and energies of up to 2.5 mJ at a repetition rate of 1 kHz. The amplified pulses will be focused into a 1-m-long differentially pumped hollow core fiber (inner core diameter of 250 μm). The spectrally broadened pulses at the output of the fiber system will be compressed by 10 bounces from double-angle technology CMs . A pair of fused silica wedges will be used to fine tune the pulse compression.

11. Optical layout of the few-cycle white light generator.

12. Optical layout of the table-top ultrafast laser

13. The homemade semi-clean room and the table-top system

14. Optical layout of the Hollow-fiber compressor.

15. Concept of the spectral phase interferometry for direct electric-field reconstruction (SPIDER)

16. Optical layout of the spectral phase interferometry for direct electric-field reconstruction (SPIDER)
Beam input

17. The 52 nm bandwidth of the Ti:sapphire oscillator at 795 nm at l0 = 795 nm and 18 fs pulse duration.

18. The autocorrelation measurement of the Ti:sapphire oscillator at 795 nm and 52 nm bandwidth.

19. Beam profile images of 2.5 mJ output beam of CPA power amplifier, which shows TEM00 Gaussian transverse distribution.

20. Temporal profile of the compressed output pulse (black curve) and temporal phase (blue curve) of the compressed output pulses measured using SPIDER. The transform limited of the output pulses after compression (green curve) is estimated to be 6.22 fs.

21. The output beam spectral broadening of about 350 nm.

22. Accurate measurement of few-cycle laser pulses using spider

23. The temporal profile change of the transform limited of the output pulses (green curve) for ICP values of 32, 44, and 54 fs, respectively at neon gas pressure of 2 atm. The compressed output pulse (black curve) and temporal phase (blue curve) of the compressed output pulses measured using SPIDER.

24. The temporal profile change of the transform limited of the output pulses (green curve) for ICP values of 32, 50, and 54 fs, respectively at neon gas pressure of 2.25 atm. The compressed output pulse (black curve) and temporal phase (blue curve) of the compressed output pulses measured using SPIDER.

25. The temporal profile change of the transform limited of the output pulses (green curve) for ICP values of 34, 54, and 56 fs, respectively at neon gas pressure of 2.5 atm. The compressed output pulse (black curve) and temporal phase (blue curve) of the compressed output pulses measured using SPIDER.

26. 3D representation of the temporal profile change of the transform limited of the output pulses (green curve) for ICP values of 34, 54, and 56 fs, respectively at different neon gas pressures from atm. The color pattern describes the output pulse from most compressed output pulse (red) to the low compressed pulse (violet) .

27. The reconstructed pulse intensity autocorrelation function IAC of the output pulses measured using SPIDER for ICP values of 32, 44, and 54 fs, respectively at neon gas pressure of 2 atm.

28. The reconstructed pulse intensity autocorrelation function IAC of the output pulses measured using SPIDER for ICP values of 32, 50, and 54 fs, respectively at neon gas pressure of 2.25 atm.

29. The reconstructed pulse intensity autocorrelation function IAC of the output pulses measured using SPIDER for ICP values of 34, 54, and 56 fs, respectively at neon gas pressure of 2.5 atm.

30. Controlled Wavelength Tuning of broad bandwidth ultrafast laser pulses

31. The variation of the pulse output beam bandwidth and peak wavelength with the input pulse chirping of A : 32 fs, B: 44 fs, C: 47 fs, D: 54 fs at fixed Ne pressure of 2.0 atm.

32. The variation of the pulse output beam bandwidth and peak wavelength with the input pulse chirping of A : 32 fs, B: 47 fs, C: 50 fs, D: 53 fs at fixed Ne pressure of 2.25 atm

33. The variation of the pulse output beam bandwidth and peak wavelength with the input pulse chirping of A : 32 fs, B: 37 fs, C: 47 fs, D: 54 fs at fixed Ne pressure of 2.5 atm.

34. Conclusions
we have demonstrated fs system which has the ability to generate pulses of 0.6 mJ with variable pulse duration from 5.35 fs to almost 13 fs and bandwidth from 23 nm to almost 240 nm depending on both, the neon gas pressure inside the hollow-fiber and the chirping of the CPA pulses.
Indeed, the observed results are important to control the progression of strong-electric-field interactions on the ultrafast time scale, and can be used in generation of higher harmonics that can be used to create more shorter pulses in the attosecond regime with shorter wavelength in the UV- x-ray regime in the forthcoming future.
08/05/2014

35. Future prospective pump-probe experiment for complex molecules

36. Future prospective pump-probe experiment for complex molecules

37. Idustrial applications
Thanks