Coherent FieldMaxII-TOP Dokumentacja Pobierz pdf (Strona 8)

Superior Reliability & Performance • www.Coherent.com • LMC.sales@coherent.com

Coherent offers three different sensor technologies (thermopile, semiconductor/optical, and pyroelectric) that address a broad

range of measurement parameters and laser characteristics.

Semiconductor sensors convert incident photons into current that can be measured by

our instruments. The photodiodes used in these types of sensors offer high sensitivity

and low noise, enabling them to detect very low light levels. They saturate above

approximately 1W/cm

, so attenuating lters must be used when operating above the

milliwatt level.

Photodiodes also have a fast response time, so they are convenient for tuning and peaking

lasers. The spectral range is more limited than our other sensor technologies. These

devices are also referred to as optical sensors. Semiconductor/optical sensors are limited

to measuring CW laser power.

Model OP-2/LM-2

LM Model Thermopiles

PM Model Thermopiles

Laser

Cross-

Reference

Index

POWER

& ENERGY

Power

Sensors

Energy

Sensors

Custom

& OEM

BEAM

DIAGNOSTICS

CALIBRATION

& SERVICE

INDICES

Product

Name

Index

Power

& Energy

Meters

Thermopile sensors are a great all-purpose technology suitable for many lasers. They are

used for measuring CW laser power, average power in pulsed lasers, and are often used to

integrate the energy of long pulses.

Thermopile sensors absorb incident laser radiation and convert it into heat. This heat

ultimately ows to a heat sink that is held at ambient temperature by either convection-

cooling or water-cooling. The temperature difference between the absorber and the heat

sink is converted into an electrical signal by a thermocouple junction.

Thermopiles operate across a wide range of input powers, and unlike a semiconductor

sensor they will not saturate. The spectral range is dependent upon the coating applied

to absorb the laser energy. The coating used on many thermopiles is broadband in

nature and is relatively at from the ultraviolet through the infrared. These sensors have

natural response times on the order of several seconds for a low power sensor and up

to one minute for a kilowatt sensor. When combined with a Coherent meter a speed-up

algorithm provides a much faster response – on the order of seconds for most sensors.

Coherent has two lines of thermopile sensors. The “LM Model” line utilizes a unique

thermopile disk in which the thermocouples are split into four quadrants, allowing the

sensors to provide beam position information in addition to power measurement. LM

Model sensors can be found on pages 22-25. The “PM Model” line incorporates traditional

thermopile disks that provide power measurement, found on pages 26-37.

Thermopile

Semiconductor/Optical

Sensor Technologies

Power and Energy Measurement Solutions

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