Coherent FieldMaxII-TOP Especificaciones descargar pdf (Pagina 52)

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To measure the energy of very high repetition rate and/or low-energy lasers, an oscilloscope can be used to monitor the

output of an EnergyMax sensor.

This page presents a step-by-step procedure for setting up an oscilloscope and using a pyroelectric EnergyMax sensor

to accurately read a peak voltage output.

Figure 1 Figure 2

Laser

Cross-

Reference

Index

POWER

& ENERGY

Power

Sensors

Energy

Sensors

Custom

& OEM

BEAM

DIAGNOSTICS

CALIBRATION

& SERVICE

INDICES

Product

Name

Index

Power

& Energy

Meters

Measuring Energy with an Oscilloscope

EnergyMax - Laser Energy Sensors

7. If you know your expected laser pulse repetition rate,

set the scope time base to show 2 pulses on the screen.

This helps set the trigger and allows observation of

the true “baseline” of the pulse. For example, for a

laser running at 10 pps, set the scope time base to

20 msec/division. Once proper triggering occurs, use

the vertical adjust to set the baseline of the

EnergyMax voltage pulse to coincide with a

horizontal grid line (see Figure 1). This setting becomes

the zero for the peak voltage reading.

8. Adjust the “time base” of the scope to show a single

EnergyMax pulse and then focus on the leading edge

to accurately read the peak voltage (see Figure 2).

To avoid affecting the calibration of the sensor

with a coaxial cable do not lengthen the cable

when using the sensor with the oscilloscope.

1. To assure the accuracy of a pulse energy

measurement, make sure the oscilloscope is

calibrated properly. Also check the date for when

the oscilloscope is due for recalibration.

2. Select a scope that has a sensitivity of at least 2 mV

and a bandwidth of at least 20 MHz.

3. To connect an EnergyMax sensor to an oscilloscope

you will need a J-POWER DB25-to-BNC accessory

(available from Coherent).

4. Use the 1 Mohm input impedance of the oscilloscope

when connecting any EnergyMax sensor.

5. Set up the scope as follows:

• Bandwidth to 20 MHz

• DC coupling

• Trigger on “+” slope and “internal” source, or use

the laser sync output and “external” source

6. Estimate the approximate EnergyMax sensor voltage

output expected, based on the Rv (V/J) of the sensor

(available on both the calibration certicate and the

calibration sticker attached to the sensor cable), and

the typical laser pulse energy.

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