Pyroelectric Detectors are sensitive over a broad spectral range. The responsivity varies very little from the ultraviolet to the infrared. We calibrate these detectors for response in V/W. The Merlin™ Control Unit can then display the reading in watts.
Stability
Because the responsivity of pyroelectric detectors is fairly temperature insensitive, you get good stability of response. The high absorptance of our durable coating has excellent long term stability.
Measurable Power
The noise equivalent power (NEP) of the 2 mm detector is 5 x 10-10 for a 1 Hz bandwidth. Since the NEP falls as bandwidth is reduced, you can, in principle, measure even lower powers if you are prepared to wait, and if all the noise is "well behaved." With reasonable electrical and acoustic shielding, we measure power levels down to a nW with a 1 s time constant at a 2:1 signal to noise ratio, in our laboratory. We regard this as a practical lower limit. The upper power limit for Merlin, with a 2 mm pyroelectric detector, is 2 mW, based on the calibration factor of 2000 V/W. With an attenuator you can measure higher powers. The lower practical limit for the 5 mm unit is approximately 3 nW due to the noise associated with the large area of the detector element.
Calibration
Each unit is calibrated at 633 nm. We do not offer detectors calibrated at more wavelengths, as the flatness of these detectors' response is quite unique and eliminates the need for more wavelength specific data. All the 2 mm units have their responsivity adjusted to 2000 V/W. The 5 mm units are shipped adjusted to 1000 V/W.
Tech Note
Lithium Tantalate Elements
These detectors use lithium tantalate crystals for high responsivity, to minimize sensitivity to microphonics and for long term stability. The crystals have a proprietary black coating to enhance the responsivity and remove the sharp spectral variations beyond 10 µm due to crystal absorption bands. We offer these detectors with either CaF2 or KRS 5 windows. This is done for detector protection and noise suppression, since these thermal detectors are very sensitive to air drafts.
Detector Systems
We offer 2 mm and 5 mm diameter detectors. The smaller detectors are useful for many laser or focused beam applications; the 5 mm models are useful for monitoring the output of a monochromator or for applications where it is not possible to tightly focus the radiation. Each pyroelectric detector package includes:
- Pyroelectric detector with window
- Detector housing with built-in preamplifier
- All necessary interconnecting cables
To complete a Merlin System, you will also need to order:
- Merlin Control Unit
- Chopper
