Overview of RM9-THz radiometer system:

User's Manual

The RM9-THz radiometer system is a sensor and optical beam chopper combination for measuring the power of very low level CW or quasi CW light sources. This sensor was specially designed for work in the terahertz range. The RM9-THz sensor has a pyroelectric element to measure a wide dynamic range of radiation, from 100nW to 100mW. It has an 8mm aperture and covers the spectral range from 0.1THz to 30THz. The system comes with the RMC1 chopper that is placed between the source and the RM9 sensor.The chopper should be mounted with the side marked "THIS SIDE TOWARD SENSOR" facing the sensor.

RM9 THz Radiometer Drawing:

Main parameters:

Problem summary:

Can I use the RM9 sensor to measure an 18 Hz pulse source without a chopper?

If the source happens to be a pulse of 18 Hz, the chopper cannot be used because it will produce a beat signal of very low frequency. However, as long as the BNC synchronizer is connected to the RM9 sensor, the RM9 can be used directly with the laser source.

Does the laser measurement depend on the distance from the laser to the sensor?

Theoretically, the beam is completely parallel and suitable for the aperture of the sensor, so there should be no difference in distance. However, if you do see such distance dependency, one of the following effects may occur：

If a thermal power sensor is used, it may actually measure the heat of the laser itself; When very close to the laser, the thermal sensor may "feel" the heat of the laser itself. However, unless the light source is weak and the heat source is strong, this will not continue to have an effect over a distance of more than a few centimeters.

The beam may not be parallel and may diverge. In general, the lower intensity flank of the beam has a greater divergence than the main part of the beam. These may lose the aperture of the sensor as the distance increases.

If you are using a diffuser based pyroelectric sensor to measure pulse energy: you may find that when you start to move the sensor close to the laser and away from it, the reading drops sharply (usually about 6%) cm in the first few times. This may be caused by multiple reflections between the diffuser and the laser device, which may cause incorrect readings at close distances. It should be at least 5 cm back from the light source, and more if the beam is not too divergent.