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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)
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.
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.
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