THIRD
YEAR LABORATORY
SYNOPSIS
OF EXPERIMENTS
Acousto
Optics
Light diffraction by acoustic waves in transparent media.
Two commercial acousto optic modulators/deflectors (flint
glass, lead molybdate) are used to gain an insight into
the similarities and differences between Bragg and Raman
Nath diffraction.
Alpha,
Beta and Gamma Radiation
Introductory nuclear counting experiments including:
Geiger tube characteristics, statistics of nuclear counting,
absorption of alpha, beta and gamma rays in various
absorbers.
Chaotic
Motion
The motion of a damped pendulum, which can be driven
into chaotic motion, is studied in real life using phase
space and Poincaré section displays. Lyapunov
exponents and correlation dimension are calculated from
the velocity time series. Software simulations are used
to clarify the principles of chaotic motion.
Coincidence
Counting
a) Introduction to the instruments and techniques used
in nuclear time coincidence counting.
b) Measurement of the spatial correlation between the
two gamma rays emitted in the annihilation of positrons
from the radioactive decay of Na-22.
c) Determination of source strength using coincidence
techniques.
Conductivity
of Germanium
The electrical conductivity of p- and n type germanium
is measured over the temperature range 170 450 K, using
a computer to monitor sample voltages and temperatures.
The data is least squares fitted. Low temp. range >
temp. dependence of electron and hole mobilities; high
temp. range > energy gap.
Electron
Paramagnetic Resonance
A 10 GHz spectrometer is used to obtain spectra of the
following:
a) copper borate > check apparatus set up; b) single
crystal and polycrystalline copper sulphate > g factor
anisotropy and directional averaging; c) manganese impurities
in fluorite > determination of hyperfine coupling
constant, super hyperfine interaction.
Electron
Probe Micro-Analysis
Electron-specimen interactions, in the electron microscope,
which result in the generation of characteristic X-rays
can be used for compositional analysis. X-ray microanalysis
can provide chemical information from volumes as small
as 1 cubic-µm in bulk specimens and is generally
the easiest technique for both qualitative and quantitative
chemical analysis. A state-of-the art electron probe
microanalyser is used to examine the composition of
a number of mixed state materials.
Electron
Tunnelling
'Aluminium oxide silver' tunnelling junctions are prepared
in a vacuum evaporator. The heights and thicknesses
of the potential barriers, due to the oxide films, are
determined from measurements of the current voltage
characteristic of each junction.
Fourier Optics
An introduction to optical image processing, employing
a CCD camera and a frame grabber to capture images:
lenses as optical Fourier transform computers, spatial
frequencies and resolution, effect of filters in the
diffraction plane on the final image, manufacture of
simple blocking filters, frequency doubling and tripling.
Fourier
Transform Spectrometry
The Michelson interferometer as a spectrometer; Fourier
transform pair relationship between the interferogram
and the incident spectral distribution. Spectra of various
light sources, effect of colour filters and detectors
with different spectral responses. Limitations: resolution,
noise, aliasing.
Frequency
Spectrum Analysis
A spectrum analyser is used to measure the Fourier components
of periodic waveforms: sine, square, pulse train, sawtooth,
amplitude and frequency modulated carrier.
Gamma
Ray Spectrometry
Properties of a NaI(Tl) scintillation detector and associated
electronics. Display of spectra from standard isotope
sources using a multi channel analyser. Energy calibration
and measurement of detector efficiency and resolution.
High
Temperature Superconductivity
Similarities and differences between Y1Ba2Cu3O?7 and
conventional type II superconductors are considered.
The critical temperature of a YBCO sample is measured
using a 4 terminal technique; the AC susceptibility
of YBCO is measured as a function of temperature between
77 K and 300 K; the magnetisation of YBCO is measured
at 77 K as a function of applied magnetic field, and
the lower critical field of the sample is determined.
Holography
Introduction to the principles and techniques of holography.
Transmission and white-light reflection holograms of
suitable objects, as well as a simple holographic transmission
interferogram, are produced.
Injection
Laser Diodes
The spectra, and light output as a function of injection
current, are measured for various kinds of laser diodes
and compared with the light emission from a red LED.
Josephson
Effects
A high temperature superconducting quantum interference
device (SQUID) is used to study the DC and AC Josephson
effects and flux quantisation.
(a) The critical current of the SQUID is measured.
(b) The value of e/h is determined from the size of
the voltage steps induced by irradiating the SQUID with
?10 GHz microwaves.
(c) The periodic change of SQUID voltage with applied
magnetic field is studied.
Magnetic
Measurements
(a) A Hall effect probe is calibrated, using a search
coil with an electronic integrator, and is then used
to measure the magnetic induction in the air gap of
an electromagnet.
(b) The magnetic susceptibilities of some paramagnetic
solutions are measured by Quincke's method. Calculation
of the ionic magnetic dipole moments leads to a consideration
of quenching of orbital angular momentum.
Magnetic
Transitions
The characteristics of an AC susceptibility bridge are
studied and the bridge is used to measure the susceptibility
of some heavy rare earth elements as a function of temperature
between 77 K and 300 K. The Curie and/or Neel temperatures
of the samples are determined, leading to a discussion
of some aspects of magnetism in the rare earths.
Magnetostriction
Small changes in the lengths of a nickel and a mild
steel rod, produced by the application of a magnetic
field, are measured by an interferometric technique
employing a laser as the light source and a photodiode
to monitor fringe displacements.
Mean
Free Path
Thin films of silver (~ 5-50nm thick) are prepared in
a vacuum evaporator. The mean free path of conduction
electrons in silver is determined from measurements
of film resistivity and thickness. Optical transmission
and interferometry are used to measure the film thicknesses
Moessbauer
Effect
A Co-57 source, driven by a linear motor, together with
a proportional counter, an amplifier and a multi-channel
analyser, are used to measure the hyperfine interactions
of Fe-57 in various absorbers at room temperature, as
follows:
a) isomer shifts in stainless steel and in ferrous and
ferric sulphates
b) the nuclear quadrupole splitting in ferrous sulphate
c) the magnetic hyperfine splitting in a-iron.
Muon
Lifetime
A large plastic scintillator, coupled to a photomultiplier,
is used to detect cosmic ray muons and their decay electrons.
The distribution of time intervals between muon entry
and decay is measured, using a time-analog converter
and a multi-channel analyser, and the mean muon lifetime
is then derived by least squares fitting the interval
distribution data.
The Neodymium YAG Laser
A Neodymium YAG laser, pumped by a semiconductor laser
diode, is set up on an optical table, using discrete
optical components; the properties of the light emitted
by both the laser diode and the YAG laser are studied
using a PC based fibre optic spectrometer.
Neutron
Irradiation
An Am-241/Be neutron source in a paraffin moderator
is used. Measurement of: half life of radioactive indium
and silver isotopes produced, induced activity as a
function of irradiation time, shielding of neutrons.
Computer simulation of moderation of neutrons.
Optical
Fibres
The fundamental properties of multimode and single mode
fibres are studied. Cleaving of fibre ends, coupling
of laser light into fibres, measurement of numerical
aperture and attenuation coefficient of a multimode
fibre, investigation of the far-field power distribution
of a single mode fibre as a function of angle.
Optical
Fibre Communication
Optical characteristics of semiconductor sources (ILDs
and LEDs), fibre coupling components (both mateable-demateable
connectors and permanent splices), wavelength division
multiplexing and demultiplexing. A fibre optic communication
link with two analog inputs is constructed.
Optical Fibre Sensors
Several intensity sensors, which exploit the optical
properties of multimode fibres, and a single mode interferometric
phase sensor are constructed. The sensitivity and resolution
of these devices are studied.
Optical
Spectroscopy
To understand the optical system and operation of a
commercial UV-Visible spectrometer. Application to the
measurement of the transmission characteristics of thin
films, optical filters, sunglasses and commercial sunscreen
lotions.
Optical
Time Domain Reflectometry
An optical time-domain reflectometer is set up, using
discrete optical components on an optical table, and
is used to measure attenuation and splicing losses in
an optical fibre.
Photo
Detector and Light Source Characteristics
A 0.22 m spectrometer, coupled to a computer, is used
to study the spectra of different light sources. The
spectral output of a tungsten filament lamp is measured
with a thermopile and the relative spectral responses
of several photo-detectors are then measured and compared.
Polarisation
of Light
A photodiode detector is used to quantitatively study
linearly, circularly and elliptically polarised laser
light produced by: scattering in suspensions, linear
polarisers, quarter wave plates, circular polarisers,
reflection from dielectrics (Fresnel's laws) and reflection
from metals.
Properties
of HeNe Laser Light
Some properties of a HeNe laser and its light are studied
including: output stability, polarisation, longitudinal
modes, wavelengths emitted, spatial and temporal coherence,
use of a pinhole spatial filter, speckle phenomena.
Pulsed
NMR and MRI
A 12 MHz spectrometer is used to illustrate the basic
principles and techniques of pulsed NMR (fid, spin-echo,
inversion recovery, Carr-Purcell) and to measure spin
spin and spin lattice relaxation times; rudimentary
Magnetic Resonance Imaging of phantoms is carried out.
Scanning
Electron Microscopy
The SEM is used in its various imaging modes to examine
a range of materials. The aim is to outline the physics
of electron-specimen interactions and image formation.
Various electron-specimen interactions and their applications
are demonstrated, including aspects of compositional
analysis using energy dispersive spectroscopy (EDS)
of X-rays to identify elements present in the sample
and electron diffraction in the form of electron channeling
patterns (ECP) to determine crystal structure and orientation.
Scanning
Tunnelling Microscopy
An instructional STM is used to introduce the principles
and techniques of scanning tunnelling microscopy, in
air, including: tip preparation, scan calibration and
atomic resolution on suitable surfaces.
Semiconductor
Band Gaps
Energy band gaps of silicon and germanium by photo ionisation
are measured by using a grating spectrometer to determine
critical wavelengths.
Sputter
Deposition
Thin films of copper, on glass substrates, are produced
in a DC magnetron sputtering unit. The effects of varying
gas pressure, substrate temperature and gas type are
monitored by checking the resistivity, optical transmission
and adhesion of the deposited films.
Transmission
Electron Microscopy
The basic operating principles of bright field (BF)
and dark field (DF) imaging and selected area electron
diffraction (SAED) in the TEM are described. SAED is
used to determine the structure types and lattice constants
of cubic type (simple, body-centred and face-centred)
single- and poly-crystal unknowns, both metal and semiconductor.
Transmission
Lines
a) Artificial line: pulse reflection by various terminations,
delay line properties, standing wave patterns under
continuous wave excitation, measurement of an unknown
complex impedance.
b) Lecher wire (excited at ?400 MHz): standing wave
patterns for short circuit, open circuit and resistive
terminations are measured using a diode detector interfaced
to a PC.
c) Time-domain reflectometer: a fast rise-time step
signal, and its reflections, allow the measurement of
the characteristics of various coaxial cables and terminations.
Waveguides
a) A 10 GHz microwave test bench is used to produce
standing wave patterns with various terminations. Measurement
of waveguide and free space wavelengths allows frequency
calibration of the microwave source (Gunn oscillator).
b) Doppler radar measurement of the velocity of moving
objects.
X-Ray
Diffraction
A commercial X-ray diffractometer is used to record
the diffraction patterns of crystals and powders of
face-centered cubic materials with sodium chloride,
diamond and zinc blende structures. Analysis of the
patterns, based on Bragg's law, includes diffracted
beam intensity and structure factor calculations.
Zeeman Effect
A Fabry-Perot étalon, a CCD camera and a frame
grabber are used to measure the splitting, by an applied
magnetic field, of the 643.8 nm spectral line emitted
from a Cd discharge lamp. The value of the Bohr magneton
is derived.
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