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Calorimeters
Frequently Asked Questions
Laser calorimetry is the measurement of laser pulse energy by determining the temperature change driven by the absorption of laser radiation by a special material which is absorbent at the given wavelength range of interest.
A laser Calorimeter is a device that determines laser pulse energy. The device records temperature changes registered by an optical absorber that is exposed to radiation emitted by a high power laser beam. These types of laser power meters are often used to measure very high levels of laser radiation not suitable for traditional power or energy sensors.
There are a few different types of laser calorimeters in the market. 1) Dual Aperture, also known as ballistic calorimeters: these calorimeters are used to measures laser pulses of high energy (~100J) and of millisecond durations. In such dual aperture calorimeters, the second aperture is used as a reference for the ambient thermal background. 2) Twin Aperture Calorimeter: Another type of laser calorimeter is the Twin Aperture calorimeter that is designed to be able to measure relatively high average powers over a period of time. 3) Vacuum Insulated Calorimeters: these devices are designed to have a very high dynamic range of power and energy sensitivity. 4) Water-cooled calorimeters: These are the most common type of laser calorimeter and consist of a water-cooled metal absorber that is heated by the laser radiation. The resulting temperature rise is measured using a thermocouple or other temperature sensor. 5) Gas-flow calorimeters: These are similar to water-cooled calorimeters but use a flowing gas, such as helium or nitrogen, to cool the absorber. The gas is then passed through a heat exchanger where its temperature rise is measured.
Peltier-Effect Calorimeters use the Peltier effect, which is a thermoelectric effect that produces a temperature difference between two materials when an electric current is passed through them. In a Peltier-effect calorimeter, a laser beam is absorbed by a thermoelectric material, which generates a temperature difference. This temperature change is then measured using a thermocouple.
These use a combination of a laser-absorbing material and a material that emits radiation in response to heating. The emitted radiation is then used to balance the absorbed energy, allowing for accurate measurements of laser power.
Calorimeters require very little sophisticated equipment, making them perfect devices for measuring small energy changes while maintaining high levels of accuracy. It is impossible to terminate all heat loss from a reaction, but calorimeters are able to minimize net heat loss to decrease this overall source of error.
It is important to carefully consider the features when selecting a laser calorimeter to ensure that it is suitable for the specific application and can provide accurate and reliable measurements. Here are the top 5 attributes to consider when selecting a laser calorimeter: 1) Absorption coefficient: The absorption coefficient is a measure of how much of the laser beam energy is absorbed by the calorimeter material. A high absorption coefficient is desirable because it allows for more accurate measurements of laser power. 2) Power range: The power range of the calorimeter should match the power range of the laser being measured. It is important to ensure that the calorimeter can handle the maximum power of the laser without being damaged. 3) Sensitivity: The sensitivity of the calorimeter determines how accurately it can measure small changes in laser power. A high sensitivity is desirable for precise measurements. 4) Response time: The response time of the calorimeter is the time it takes to reach thermal equilibrium after being exposed to the laser beam. A fast response time is important for measuring pulsed lasers and for minimizing thermal drift. 5) Size and portability: The size and portability of the calorimeter may be important depending on the specific application. A smaller and more portable calorimeter may be more convenient for field measurements, while a larger and more stable calorimeter may be more suitable for laboratory use.
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