Experiment and equipment
The experiment aims to measure the specularity of a laser beam reflected from an ice or water surface, and is described in detail here. A guide to performing the experiment can be found here. Before starting work on the experiment, you should read the safety notes
532nm Diode Laser Pointer
Image: made-in-china.com
The laser continuously emits light at 532nm (green) from a laser diode. Before attenuation, the laser beam has 1mW of power. The laser is a diode pumped solid state frequency-doubled, or DPSSFD, laser. The green light is generated indirectly. A high power infrared laser diode at 808nm pumps a crystal Nd:YVO4 which lases deeper in the infrared at 1064nm. Another crystal frequency then doubles this light to the output wavelength of 532nm.
Peltier Cooler
Image: wikimedia.org
The Peltier cooler is an active heat pump which transfers heat from one side of the device to the other. Electrical energy is consumed as heat is transferred against the temperature gradient i.e. from the cold side to the hot side. The amount of cooling possible with the Peltier depends on the current applied to it and how well the heat is removed from the hot side. Peltier coolers are very useful. You can find them in mini-fridges, computers, cameras, telescopes and even satellites!
Photodiode
Image: thorlabs.com
The photodiode converts light incident upon its surface into an electrical voltage. When a photon of sufficient energy strikes the Silicon surface, an electron is excited and a photocurrent is produced. Silicon-based photodiodes generate very little noise, but they are sensitive to a huge wavelength range (190nm to 1100nm). Therefore it is important to reduce the amount of unwanted background light that reaches the photodiode surface.
Polarizing Filter
Image: wikimedia.org
The polariser sheet converts unpolarised light into polarised light. It is made from a sheet of polyvinyl alcohol that has been stretched in one direct and stained with polymeric iodine. This results in light being blocked if it is not parallel to the direction in which the material was stretched.
Metal Mirror
Image: thorlabs.com
The mirror is coated in silver so that it reflects the green light from the laser. It also extremely flat and reflects more than 98% of the incident light.
Thermistor
Image: digikey.com
The thermistor is a resistor whose resistance varies with temperature. Specifically, as the resistance of the device decreases with increasing temperature, the device is known as a negative temperature coefficient or NTC thermistor. The thermistor is made from a semiconductor material. In a semiconductor, an increase in temperature increases the number of free electrons in the material. Therefore when the temperature increases, the current increases and the resistance decreases. The output of your thermistor is linear - there is a linear relationship between temperature and output current/voltage.
National Insturments DAQ Card
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The data acquisition or DAQ card is an interface between the computer and the experiment. It converts the analogue signals from the photodiode and thermistor into digital signals which can be processed on the computer. The device is plugged in via USB and the digital information is passed directly to the LabVIEW software so that it can be viewed in real time.