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)