This page is a collection of the experiments from the physics senior laboratory in TUDublin. Like the photography pages on my site, it will be a page that will be updated regularly with new additional content. All illustrations made by me. For more information on the experiments, feel free to contact me through my contact page. I am always looking for interesting new experiments to construct to be used as demonstrations, as part of the syllabus or projects so if you want to make contact to share details that would be appreciated.
This apparatus manufactured and sold by Teachspin is the double-slit experiment for light. The apparatus comprises of two experiments. The first experiment uses a red diode laser as a light source to create an interference pattern. By using a small vertical aperture mounted on a horizontal translation stage and located at the entrance aperture to a photodiode, the light intensity can be measures as a function of position. The resulting measurements are graphically ploted. The second experiment involves the use of a broad band light source from a bulb. A In front of the bulb a narrow band dichroic filter tuned to 550 nm is adapted onto its output aperture. A photomultiplier tube located in the light tight control box at the other end of the light path seen in the illustration, allows detection of single photons. Thus it is possible with this apparatus to measure an interference pattern generated by a single photon interfering with itself as it passes through a double slit. However, measuring this is quite a challenge as these weak signals are buried in the noise. Perhaps the dificulties of the experiment could be overcome using a lock-in amplifier which can detect such faint signals.
This Atomic Force Microscope (AFM) manufactured by Easy Scan is limited to Contact Mode. The AFM works by the projection of a laser beam from a laser diode, onto cantilever which in turn reflects the light onto a photodiode array. Deflection of the cantilever causes the light to fall on different regions of the array and so the PD registers a different voltage. The voltage is translated into position.....
This apparatus is the Modern Interferometery kit. The apparatus comprises components for the assembly of various interferometers on an optical breadboard. Interferometers include the Michelson, Quadrature Michelson, Sagnac, and the Mach-Zehnder configurations. The illustration (below) shows the Sagnac interferometer with a gas cell located in one arm of the interferometer. The air pressure inside of the cell can be adjusted by means of a hand pump. When the pressure is increased there is a corresponding change in the the optical path length and so the photodiode detects the number of fringes that pass. Armed with this information, the refractive index of the gas inside the cell can be calculated.
The configuration (below) is the quadrature Michelson interferometer. A sample metal bar is placed inside a coil and a relatively large current (several Amps) is channelled through the coil. Thermal energy is dissipated in the sample contained within its core. As such, the sample expands. By positioning the sample between a spring-loaded translation mirror and micrometer head, the expansion/contraction of the sample causes the mirror to shift ever so slightly. With this apparatus, it is possible the measure the expansion of the material with an accuracy to half the wavelength of red light.
The experiment consists of a single mode optical fiber which relays plane polarised 'monochromatic' light from source to detector. For each instance of a taut fiber and helically wound fiber, the output current from a photocell is measured with respect to the angle of polarisation of the light incident on the detector. The light source used is a laser with an output of around 650 nm.
To be continued.....