A Growing Tall Poppies in Science Project Provided by: CXS Centre of Excellence, Santa Maria

College and AKORN Educational Services

An Extreme Ultra-Science Week:

Ultra-Violet (UV) Semiconductors

and Ultrafast Extreme Ultraviolet

Lasers (XUV)

September 8th

-14th

2010

Short Wavelength Laser Program

Mentors: Christopher Hall & Khuong Dinh

Angela Selleck, Hillary Moutia, Natalie Relf, Sarah

Lockwood, Gwynneth Cheale and Katie Zhang

St Catherine’s School

Growing Tall Poppies 08/09/10 - 14/09/10

This week we worked at Swinburne University, in the CAOUS centre through the

‘Growing Tall Poppies’ program and Akorn. With the help of two mentors:

Christopher Hall and Khuong Dinh, we conducted two experiments in one of the

scientific laboratories. On Wednesday, we had many introductory speakers who

introduced us to Swinburne and the work that they did there.

On Thursday we participated in two practicals: our first practical looked at the

emission wavelength and intensity of the UV laser of different Quantum Wells,

consisting of ZnO and ZnMgO. The second practical was looking at the intensity of a

fundamental laser by changing the gas pressure inside the gas cell of the HHG

apparatus.

We went to the Australian Synchrotron in Monash University on Friday afternoon.

This was a very informative experience where we had a guided tour of the facility.

We were lucky enough to see the Synchrotron when it was not functioning, which

only occurs two or three times a year. This meant we were able to see some of the

equipment and understand how it works, such as the undulator and the wiggler.

Over the next two days we analysed our results from the practicals, with the help of

our mentors. These are our findings…

Acknowledgments:

• The ARC Centre of Excellence for Coherent X-Ray Science (Swinburne

University)

• Mentors: Christopher Hall & Khuong Dinh (Short Wavelength LASER

Program)

• The Growing Tall Poppies Program Director: Dr Eroia Barone-Nugent Santa

Maria College

• AKORN Educational Services: Lisa Portlock & Georgene Bridgeman

• Guest Speakers: Prof. Lap Van Dao, Jeff Davis, Brenton Hall, Chris Vale &

Evelyn Cannon

• Supported by: NAB Schools First & Catholic Education Office

INTRODUCTION

This project is about LASER technology and applying it to various experiments that

haven’t been conducted previously.

This research is important because it will help develop new drugs/medications,

research new devices, make cheaper LEDs and apply UV Lasers and LEDs to

improve data storage, laser eye surgery, micromachining, sterilisation and research. It

can help society through improving current drugs and technology as well as research

in areas such as biology and medicine. There is currently a high demand for lasers

with a spectral range from 4nm -30 nm and from 300nm- 400nm.

High school students should care about the physical sciences as it is part of our

everyday life and works towards the advancement of society through different areas

of science. The potential career path opportunities include various engineers and

researchers (CSIRO). At this stage of science it is important that we study a range of

sciences as they are becoming interdisciplinary, this is evident in our practicals as the

information that we have gathered can be used in areas of science other than physics.

Laser oscillator and a 2 stage

laser amplifier

HHG apparatus

EXPERIMENT 1

Aim: To identify the behaviour of different Quantum Wells and how they can be

useful.

We want to analyse the temperature dependence (in Kelvin) of the emission

wavelength and intensity of a ZnO Quantum Well. We also want to observe how

the ZnO Quantum Well width affects the emission wavelength and intensity.

Hypothesis: If the temperature is raised then the intensity will decrease.

Materials:

ZnO Quantum Well (sample 1: QW width 2nm, sample 2: QW width 4nm)

Mirror adjustment

Safety goggles

IR viewer

Computer (with mouse)

Femtosecond UV LASER

Figure A:

Method:

1. Optical set up as shown in Figure A

2. Adjust knobs on the mirror to maximise signal in

spectrometer

3. Set temp. to 20K

4. Run programme

5. Record spectrum on computer (computer)

6. Repeat steps 1-4 using different temp. (ie. 50K,

80K, 130K, 160K, 220K, 260K)

Results:

Figure 1. Sample 1

Figure 2. Sample 2

Discussion:

We are examining ZnO Quantum Wells because they can by used to generate UV

light. Two sets of results were taken, one using 2nm ZnO Quantum Well and the

other using a 4nm ZnO Quantum Well, shown as Figure 1 and Figure 2

respectively.

In Figure 1, we see that as we raised the temperature the intensity decreases and

the peaks stay in relatively the same position. However there is an irregularity in

our findings as the first result peaks at the third highest point, yet all other peaks

occurred in order. We have reason to think that this is a human error as in the

second set of results this irregularity does not occur. This might have been caused

because of a shift in the alignment of the mirror or another human error.

In Figure 1 the second peak occurs relatively close to the first peak ranging from

352.5nm to 358nm. The first peak occurs at a higher intensity than the second

peak for 50k and 80k, however the first peak occurs lower than the second peak

for the other samples. This is because the probability of radiative re-combination

is greater within the ZnO in the Quantum Well than ZnMgO on the outside of the

Quantum Well at higher temperatures. This also occurs in Figure 2.

In Figure 2, we see that the first peak (322.5 nm) occurs at same position as in the

Figure 1. However the second peak (374 nm) occurs at a longer wavelength and at

a greater intensity.

From this we can conclude that the first peak was formed from the ZnMgO on the

outer of the Quantum Well and the second peak is formed from the ZnO in the

centre of the Quantum Well.

Conclusion:

We successfully achieved our aim of observing the difference of changing

temperatures to measure the effect on intensity. This proved that our hypothesis

was correct and that the intensity decreased when the temperature was raised.

Increasing the temperature also produces a shift in the centre of each emissions

peak. Changing the width of the Quantum Well changes the position of the second

peak.

EXPERIMENT 2

Aim: To investigate the wavelength and intensity of the high harmonic generation

signal by varying the gas pressure inside the gas cell.

Hypothesis: If the pressure inside the gas cell is larger, then the HHG intensity will

be less intense and have a longer wavelength.

Materials:

Argon Gas

Computer (with mouse)

LASER

Vacuum Spectrometer

HHG apparatus

Method: 1. We adjusted the gas pressure to 54T (optimum)

2. Measure wavelengths using computer software

3. Adjust to 40T and measure wavelengths

4. Adjust 80T and measure wavelengths

GGaass cceellll

Laser oscillator and a 2 stage

laser amplifier

HHG apparatus

Results:

Discussion:

The 3 step model is used to explain the HHG process:

1. The laser field breaks the coulomb barrier which allows the electrons to tunnel

out of the atom.

2. The free electrons then gain momentum within the electric field.

3. The electron recombines with its parent ion and emits a photon which gives

off a higher energy.

In our experiment we generated the HHG with Argon.

HHG (high harmonic generation) is the method for generating short wavelength light.

Torrs is the measurement of the amount of gas pressure we used to find out the

different wavelengths in nanometres.

The intensity (HHG) depends on the phase matching condition, which depends on the

laser, focus length and the gas pressure in the gas cell. The laser and the focus length

were kept constant, only the gas pressure was changed.

When we changed the pressure from the optimum pressure (54T) the intensity of the

HHG decreased, because as we did it with 80T it substantially decreased.

Conclusion:

We proved our hypothesis correct and achieved our aim of investigating the

wavelength and intensity of the high harmonic generation signal by varying the gas

pressure inside the gas cell.

APPENDICES

An Extreme Ultra-Science Week : Ultra-Violet (UV) Semiconductors

and Ultrafast Extreme Ultraviolet Lasers (XUV)

September 8th

– 14th

2010

Short Wavelength Laser Program

Mentors: Christopher Hall, Khuong Dinh

Your Brief

A. You will work with your mentors in the Laser group to identify the behaviour

of different alloys and relate the information to how it can be useful.

B. You will also create a photo-story of your week. It will include action shots of

students and mentors and interesting things you find out at the synchrotron. It

will identify in picture form what you find interesting, why the research is

meaningful and why we should care about the research.

Your Report

You will produce a report about the work of the Short Wave Laser Group. This can be

in the form of your own choosing e.g. a newspaper report or a journal article (e.g.

New Scientist)

The short report should include some of the basic science and also:

You will need to articulate:

Why this research is important

How it is connected to real world problems and how can it help society,

individuals

Why high school students should care about the physical sciences/potential

career paths

How and why it is relevant to the interdisciplinary approach the CXS groups

are taking

Presentation

You will also work together to present a power point presentation at the end of the

week. You will include:

How working on the diffraction tube development changed the way you learnt

the science, and how it felt if it worked or not

Scientific questions you had/posed for investigation during the week-even

ones that did not get answered

How your perception of the physical sciences and scientists may have changed

Introduction

Something about light and lasers: Light travels at 3x108 metres per second.

The laser is an instrument that can produce light with very well defined wavelength.

A laser may also be pulsed, producing high energy pulses with a short duration.

Many techniques are available for controlling the pulse duration, intensity and

wavelength. These parameters can be controlled extremely precisely, allowing

scientists to tailer experiments to their specific needs. The femtosecond laser is able

to produce a pulse of light on the scale of 10-15

seconds (1 fsec) in duration. These

typically produce light in the near-infrared region, however there ways of converting

this light to visible light and invisible light such as X-rays. Having precise amounts of

light delivered to atoms or molecules allows us to examine how molecules or atoms

behave in a way that cannot be studied otherwise. New lasers and techniques are

constantly becoming available and being discovered, allowing scientists to perform

new and exciting research (for example, Swinburne researchers are examining new

materials that may be used to produce lasers that operate in the ultraviolet region of

the light spectrum).

How far would light travel in 1 femtosecond? Well 3x 10-7

m. To compare, the size of

an atom is typically 10-10

metres wide. The pulses of light produced by these lasers are

very short and very powerful. The Swinburne ultrafast spectroscopy femtosecond

laser delivers 100 x 10-15

(100 fsec) of visible light, and the molecules being studied

are measured using a spectrometer. The laser used to produce X-rays produces 30 x

10-15

(30 fsec) pulses to study atoms. The resulting X-ray pulses are even shorter.

UV Semiconductors

Alloys are combinations of different materials e.g. copper and tin gives an alloy of

bronze. These are metals but other materials can form semiconductor alloys, such as

zinc oxide. This is a semiconductor material which has many potential device

applications. A semiconductor is a substance that can conduct electricity under

certain conditions. These materials can be customised in order to control their

electrical and optical properties. The compound of interest here is Zinc Oxide.

Quantum well structures of ZnO contain a very thin layer of ZnO, even down to a

single nanometer thick. The special thing about quantum wells is that the crystal

lattice is so thin, the electronic energy levels of the crystal lattice are changed. By

precisely controlling the thickness of the quantum well we can control the optical and

electronic properties of the material. These structures of ZnO could potentially be

used to produce ultraviolet lasers anywhere in the 400-300 nm range. UV lasers have

many applications, including Blue-Ray disc players, laser eye surgery, micro-

machining, fibre-optic sensor manufacturing, materials research, dermatology

(medicine) and a myriad of industrial uses.

XUV lasers

Coherent extreme ultraviolet (XUV) radiation and soft X-ray radiation have a wide

range of applications in physics, chemistry, and biology. At Swinburne, coherent

XUV radiation is produced by high-order harmonic generation (HHG) of highly

energetic femtosecond laser pulses in noble gases. Using different noble gases, argon,

neon and helium, we are able to generate HHG with very defined wavelengths in the

spectral range 8–35 nm. The extreme ultraviolet radiation is applied to study

dynamics of diatomic molecules and atomic systems and also for coherent diffractive

imaging (CDI). CDI is a well establish technique that enables the structure, shape and

size of biological cells and molecules (information which is important for biology,

medicine and pharmaceutical research) to be determined. This kind of experiment is

could almost be considered as smaller version of the Australian Synchrotron.

PowerPoint

Presentation