PHYS 397: List of Experiments Jan 2001

Established experiments:

1) AC Measurements and Techniques

In most experiments the precision with which measurements can be made is restricted by random fluctuations, usually called noise. One way of dealing with electrical noise is to use careful shielding, the other way is to use frequency filtering techniques. In this experiment we lead you into improving the sensitivity of magnetic field measurements using the Hall effect probe by going from DC amplification to tuned amplifiers and lock-in amplifier techniques. The experiment does not have to be confined to investigating Hall effect probes.

2) Black Body Radiation (new improved version ready by Experiment #2 sign-up in February!)

Although this experiment is billed as an investigation of black body radiation, it is much more an investigation of the techniques required to make high sensitivity measurements of low-level visible and near infrared radiation using a spectrometer and thermopile detector. The confirmation of the Stefan-Boltzmann Law is one of the standard experiments that can be done. Maybe you can succeed in confirming the Planck Law.

3) Compound Lenses and Matrix Approach

We supply an optical bench and a variety of lenses and filters to give you the opportunity to try out in real life what was covered in Physics 362 under the headings of lenses, optical systems and aberrations. We particularly suggest, after having calibrated the individual lenses, to compare three lens combinations with matrix algebra predictions. You may wish to try using the CCD array to determine image sharpness. (CCD camera may be added later in term.)

4) Doppler Shift of Microwaves

The Doppler effect of sound waves is covered well in junior courses. In this experiment we examine the Doppler effect using electromagnetic radiation (microwaves) and try to understand how it works. In particular, we utilize the principle of the homodyne Doppler technique to measure the velocity of a moving car on a track. This is precisely the idea behind the police radar trap! The frequency from the transmitter is mixed (homodyned) with the reflected frequency from a moving car, and a frequency difference is observed on an oscilloscope. Another way of analyzing the system is to think of two beams interfering and measuring the beat frequency.

5) Fiber Optics

Information transmission is rapidly being shifted from electrical signals on cables and microwave relay systems to optical signals sent over thin glass fibers. Fiber systems have many orders of magnitude greater bandwidth and therefore can carry much more information. They are also less sensitive to external interference and need less energy to transmit signals over large distances. We have some of the basic equipment that will allow you to become familiar with optical fibers and their advantages and disadvantages for communication.

6) Fresnel Diffraction

A long dark stove pipe assembly and a HeNe laser source allows you to explore the diffraction of light due to various obstacles in the light's path and to confirm what you learned in optics courses. The diffraction patterns can be photographed or detected with a CCD array and then analyzed.

7) Holography

We have a darkroom, a reasonably vibration-free optical table, mirrors, lenses, filters, laser source and a (limited) supply of holographic film, for you to learn how to make holograms of small 3-D objects. Different types of holograms can be tried: transmission, reflection, interference, multi-exposure, etc.

8) Interferometers (Michelson & Fabry-Perot)

Interferometers are devices that produce interference patterns due to the splitting of light (or other radiation). There are many types of interferometers including wavefront-splitting and amplitude splitting. In this experiment, you will examine a Michelson interferometer and a Fabry-Perot interferometer. In particular, compare how well each type can resolve a very small difference in wavelength - first starting with a sodium doublet and onto more difficult topics such as hyperfine structure of mercury. The Fabry-Perot interferometer can be used in two ways: moveable mirror and fixed mirror configurations. A good working knowledge of the Fabry-Perot interferometer is needed in performing the Zeeman Effect experiment.

8b) Zeeman Effect and Fabry-Perot Interferometer

As a follow-up to experiments with the Fabry-Perot interferometer, you may wish to use it to measure the Zeeman splitting of the mercury green line. The interferometer must first be calibrated using a known wavelength to determine its gear ratio.

9) Lumped Parameter Delay Line (Model of Transmission Line) (not fully operational at this point, but may be modified later in term)

Any electrical transmission line affects the signal that is being transmitted. Electrical resistance is the most common cause, but two wires in close proximity will also have capacitance and inductance per unit length as hidden components. Inductance and capacitance are minimized in coaxial cables, which therefore become the conductors of choice for high frequency applications. Knowing the frequency limitations and the proper termination characteristics of cables is of great practical importance. The extremely high frequencies at which the standard coaxial cable reaches its limits makes it difficult to deal with in the lab. We therefore simulate a coaxial cable with a string of discrete "L" and "C" components which shifts the characteristics to a more accessible frequency range. You can explore termination characteristics, cut-off frequencies, transmission delays and whatever else you like.

11) Nuclear Scintillation

We have a scintillation counter sensitive to gamma rays and capable of discriminating between gamma rays of different energies. A computer interface allows you to plot gamma ray spectra quickly and easily after the basic electronics has been made to work. After setting up the equipment and doing some calibrations with known radioactive sources, you can for example study unknown sources, gamma ray absorption characteristics, Compton edge and resolution of the equipment.

12) Optical Barrier Penetration (Quantum Tunneling)

The classical theory of Electromagnetism predicts that an electromagnetic wave (light) will penetrate into a barrier at angles greater than the critical angle of refection. If the barrier consists of a thin gap, some of the light will pass through the gap in what is called frustrated total internal reflection. This phenomena can also be interpreted in terms of Quantum Mechanics as an example of quantum tunneling across a potential barrier. In this experiment, you will be given a laser and a Newton's rings apparatus to provide a variable thickness gap. You can then compare the transmission and reflection amplitudes that result with the predictions of Electromagnetism and Quantum Mechanics.

13) Optical Fourier Transforms (new improved version ready by Experiment #2 sign-up!)

We usually think of Fourier transforms in an electrical sense, such as the frequency components which make up a square wave, and what happens to such wave forms when either high or low frequency components are removed by filtering. Repetitive optical images (e.g. a series of parallel lines) too can have fine detail and coarser repetitive elements, equivalent to high and low frequencies in electrical signals, which can be filtered using diffraction techniques. The experiment allows you to explore the techniques involved in Fourier optics.

14) Single Photon Interference

Interference and diffraction are explained as wave aspects of light. With a cooled photomultiplier tube, it is relatively easy to detect individual visible light photons. It is also possible to create sufficiently dim light conditions such that it can be shown that no more than one photon at a time would be present inside a box such as you would be using. If such a dilute stream of photons in a beam is aimed at a double slit, and the photons, one by one, are counted where otherwise a double slit interference pattern is to appear, what do you expect to detect? Try it.

15) Sound Waves in a Box

This experiment involves the investigation of sound waves in a narrow 2D box. In particular you determine the various resonant modes and compare to theoretical predictions. A small transmitter (microphone) is used to emit sound waves and a second microphone (detector) is used to measure the locations of the resonant peaks on an X-Y grid.

16) Thermodynamics of the Peltier Cell

The Peltier cell works on the principle of the thermoelectric effect "in reverse". You should be familiar with a thermocouple, which involves a temperature difference to produce an EMF. By forcing a known current (emf) through a Peltier cell, a specific temperature can be attained. The emphasis of this lab is on the "thermodynamics" of the Peltier cell.

17) Ultrasonic Diffraction of Laser Light

Acoustical waves in liquids cause density changes with spacing determined by the frequency and the speed of the sound wave. For ultrasonic waves with frequencies in the MHz range, the spacing between the high and low density regions are similar to the spacing used in diffraction gratings. Since these density changes in liquids will cause changes in the index of refraction of the liquid, it can be shown that laser light passed through the excited liquid will be diffracted much as if it had passed through a grating. Raman-Nath diffraction is slightly different from diffraction from a ruled grating, and you should try to investigate the difference. The experiment can serve as a good, indirect method of measuring the velocity of sound in various liquids and solutions. There are also details in theory and practice which are by no means obvious. Furthermore, striation phenomena can also be used to measure velocity of sound.

18) Vacuum Technology & Thin Film Deposition (with Bell Jar) (completely new version under development; possibly available by Experiment #3 sign-up)

Today's technology, be it x-rays, computer chips, light bulbs, or nuclear accelerators, would be impossible without the routine capability to achieve a good vacuum. The purpose of the experiment is for you to gain some experience with basic vacuum techniques and to make measurements which require a vacuum. The pumping station comes complete with gauges and is set up with a bell jar for evaporation of thin metal films.

19) X-rays

Theses are table-top units operating at either 20 or 30 kV with copper target anodes. A wide variety of X-ray measurements can be done. We list: Bragg diffraction off some cubic crystals, absorption and Moseley's law, radiography, and a rough determination of Planck's constant. In a sense, two approaches can be taken. One is to assume the basic properties of X-rays and use them to do crystallography. The other approach is to make use of crystallography to create monochromatic X-rays, and then investigate the properties of X-rays of different wavelengths.

New experiments (to appear later in term – exact date of installation not known):

20) Scanning Tunneling Microscope (STM)

You will be able to image atoms with this microscope.

21) Pulsed Nuclear Magnetic Resonance (NMR)

Learn the basic principles of pulsed NMR. (The same principles apply to MRI – magnetic resonance imaging – used in hospitals.)

Other new equipment:

- digital sampling oscilloscopes (60 MHz, 100 MHz and 300 MHz bandwidths) – can print out waveforms

- computers for data acquisition

- new CCD cameras for image acquisition (available soon)