two color high harmonic generation · 2015-07-31 · laser pulses that have a very short duration...
TRANSCRIPT
Sean Buczek
Ultrafast Lasers Laser pulses that have a very short duration
Picoseconds and shorter
Need specialized laser sources for this Free Electron Lasers are nice, but too costly for most labs
Ti:Sapphire is the most common tabletop laser used in the field
Shorter pulses are needed Short pulses = Faster camera
Image credit: https://upload.wikimedia.org/wikipedia/commons/7/73/The_Horse_in_Motion.jpg
High Harmonic Generation High intensity laser (1014 W/cm2) through a noble gas
Three Step Model[1]
http://www.uni-muenster.de/imperia/md/images/physik_pi/zacharias/research/hh/high_order_harmonic_generation.png
http://www.uni-muenster.de/Physik.PI/Zacharias/en/research/hh/hhg.html [1] P.B. Corkum, Phys. Rev. Lett. 71, 1994
High Harmonic Generation Two different possible electron trajectory
Long and short
Long trajectory electrons contribute less to the total HHG spectra[2]
Able to create VUV-XUV wavelengths (200-10nm)
Very short wavelength allows for sub-femtosecond pulsesForms a train of attosecond pulses[3]
Limited flux
Low conversion efficiency: much lower pulse energy
Greater flux is needed for many experiments [2] Jin et al., Nature Communications 5, 4003 (2014) [3] Zenghu Chang, Fundamentals of Attosecond Optics (Boca Raton: CRC Press, 2011)
HHG using Two Colors To increase photon flux[2]
Optimizes short trajectory of electron
2 order of magnitude increase over single color driving field possible
Pulses are more separated in attosecond pulse train
Intensity of individual pulses increases
[2] Jin et al., Nature Communications 5, 4003 (2014)
Experiment Overview Confirm HHG using fundamental (800 nm) and second
harmonic (400 nm)
Significant increase in flux over single color expected
Observe oscillations in flux due to phase relation between the two colors
Use HITS laser at J.R. Macdonald Lab at Kansas State University[4]
[4] Langdon et al., Optics Express 23, 4563 (2015)
800/400
Delay Stage
SHG BBO
From HITS
Telescope to shrink HITS to 15 mm
Semi-infinite Gas Cell f = 1m
l/2 WP “specs”: Input 6mJ@800nm Interferometer Output: 3mJ@800nm 1.9mJ@400nm
Experimental Setup
Harmonic Spectra (log)
900 1000 1100 1200 1300 1400 1500 1600 1700 1800 190010
1
102
103
104
105
raw pixel
yiel
d (
raw
)
800+400
400
800
Increasing energy
H8 H9 H10 H11
H12 H13
H14 H15
H16
Conclusions Were able to see a two order of magnitude increase in
the flux of the high harmonics
Oscillations in flux were visible, but a more stable apparatus is needed for further study
Showed that third harmonic generation is possible using our setup
Were able to generate third harmonic, but did not have time to generate high harmonics with it
Future Interests Two color HHG using fundamental and third harmonics
In theory, this gives an even greater increase in flux
Experimentally confirm the ability to selectively increase harmonics using chirped pulses[5]
[5] Xu Wang et al., Phys. Rev. A 90, 0.23416
Acknowledgements Travis Severt, Jan Tross, and Pratap Timilsina
Itzik Ben-Itzhak and Carlos Trallero and their groups at Kansas State University
Funding provided by NSF MRI (The laser), NSF EPSCOR (Travis, equipment, maybe others), DOE (laser), NSF REU (me)
Oscillation Explained A graph of the superposition of two cosine functions
describing the two lasers
Simplified form of the affects of a slowly shifting time overlap between the two colors
Field will affect the trajectory of electrons
Oscillation Example 800 and 400nm p-pol.
15 16 17 18 19 20 21 22 23 24 250.2
0.4
0.6
0.8
1
1.2
1.4
1.6
delay (fs) (66as resolution)
yiel
d [a
.u.]
H10
H14
H8
H17
yiel
d (
arb
itra
ry u
nit
s)