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Microscope Slide Power Meter Sensor Heads
S170C Microscope Slide Power Meter Sensor used with a 1.30 NA Objective and Shown on an MLS203-1 Motorized Scanning Stage Equipped
High-Power Microscope Slide Power Sensor for UV, Visible, and IR
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The back of the microscope slide sensor housing is engraved with the sensor specifications and a grid for centering the beam on the sensor. This image shows the engravings on the S170C; the engravings on the S175C are shown further below.
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Using the engraved alignment target on the back of the sensor housing, a user can position the stage so that when the sensor is flipped, the beam strikes the center of the sensor. The S170C is shown in this image.
Thorlabs' Microscope Slide Power Sensor Heads are designed to measure optical power at the sample in microscopy setups. These sensor heads have the same footprint (76.0 mm x 25.2 mm) as a standard microscope slide and are compatible with most standard upright and inverted microscopes. The sensors have a large active sensor area (18 mm x 18 mm); the low-power version incorporates a silicon photodiode sensor, while the high-power version is equipped with a thermal sensor.
The low-power sensor is sensitive to wavelengths between 350 nm and 1100 nm at optical powers between 10 nW and 150 mW. A <1 µs response time makes this sensor ideal for high-resolution measurements using lasers, but it is still well suited for measurements of broadband illumination sources, like LEDs and white light sources. The high-power sensor is sensitive to wavelengths from 300 nm to 10.6 µm at optical powers between 100 µW and 2 W. This sensor features a flat absorptivity over the specified wavelength range, making it ideal for measurements of broadband illumination sources, like LEDs and white light sources. Please see the Specs tab for more information.
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The S170C connected to the PM200 touch screen power meter console (sold separately).
As seen in the image above, the bottom of the S170C and S175C sensors feature a laser-engraved alignment crosshair that marks the active sensor area to aid in aligning and focusing the beam. To use with a standard upright microscope, insert the housing into the beam path so that the engraved side is facing the objective of your microscope. Once the power sensor is centered under the objective, turn the slide over so that the detector is facing the beam in order to take a power measurement. For inverted microscopes, place the detector in your slide holder with the sensor facing the objective and turn on the trans-illumination lamp. Centering the beam on the engraved target will center the sensor in the optical path.
Power Meter Console Compatibility
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Typical responsivity curve for the silicon photodiode in the S170C. Note that this curve is representative, and the actual responsivity across the spectrum will vary from unit to unit.
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Typical absorption curve for the S175C (glass and absorber). Note that this curve is representative, and the actual absorption across the spectrum will vary from unit to unit.
An illustration to show the behavior of light exiting a high NA objective after it enters the S170C microscope power sensor head vs. a typical photodiode sensor. For objectives with NAs greater than 1.0 and a detector without index matching gel in the gap, some of the light will also undergo total internal reflection at the ND filter-air interface, causing additional losses before the light reaches the sensor. (Important Note: Do not place immersion oil or other immersion media directly on the ND filter of any Thorlabs photodiode detectors other than the S170C, as they were not designed for this application and the oil cannot be cleaned from the filter surface.)
Large Active Area and Index Matching Gel
The S170C and S175C microscope slide sensor heads were designed with large-active-area detectors to accommodate high NA objectives. In addition, the S170C uses index matching gel in the gap between the neutral density filter and the sensor to minimize losses due to internal reflections at the air-glass interface. The S175C uses a protective glass cover that features a smaller air gap than the S170C (0.15 mm versus 1.5 mm) to avoid the use of index matching gel, which helps maintain a fast sensor response time.
The schematic to the right illustrates the advantages that a large-area detector like the one used in the S170C provides over typical photodetectors by tracing the path of light from a high NA objective after it enters an S170C microscope slide sensor head and a typical photodiode sensor. The typical photodiode sensor shown in the drawing has an air-filled gap between the ND filtera and the sensor and a Ø9.5 mm active area, similar to our S130 slim photodiode sensors or S120 standard photodiode sensors. When light from a large NA objective reaches the interface between the ND filter and the glass, it refracts away from the center of the sensor. Some of the light misses the edge of the small active area of the photodiode, causing erroneous power measurements.
In the S170C microscope slide sensor head, the gap between the neutral density filter and the sensor active area has been filled with an index matching gel. Compared to the ND-filter-to-air interface in typical sensor heads, the gel minimizes the amount of reflected light at the ND-filter-to-gel interface that would otherwise not reach the sensor and eliminates refraction of light exiting the ND filter, allowing the large-area detector to capture more light from the objective. Please be aware that this design cannot completely compensate for this effect for very high NA oil objectives and at certain wavelengths.
Similar results would be expected from a comparison of the S175C with other thermal sensors. The small 0.15 mm air gap between the protective glass plate and the thermal sensor minimizes the light refracted away from the center of the sensor, while the large 18 mm x 18 mm active area catches more of the incoming signal. Additionally, the S175C has a protective class cover plate that allows the appropriate immersion media for the objective to be applied without damaging the sensor. (Note: do not apply immersion media to Thorlabs' other thermal sensors, as it may damage to the sensor head.)
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The S170C may be post mounted via the 8-32 (M4) tap in the side of the housing.
The S170C Microscope Slide Power Meter Photodiode Sensor Head is designed to fit in the microscope slide holders of standard upright and inverted microscopes to measure the power at the sample plane. The active sensor is contained within a sealed housing, behind a neutral density (ND) filter with OD 1.5. A 20 mm x 20 mm indent above the ND filter accepts cover slips and immersion media. Immersion media (water, glycerol, oil, etc.) may be placed in this well directly over the ND filter, or a cover slip may be inserted first to simplify clean up. With a fast response time of 1 µs, minimum power of 10 nW, and resolution of 1 nW, this photodiode sensor is ideal for high-resolution power measurements of low-power illumination.
The back of the slide is engraved with the sensor specifications and a grid for aligning the beam. To take a power measurement, simply flip over the slide to expose the sensor to the objective. In inverted microscopes, the trans-illlumination lamp can be centered on the grid to ensure the sensor is centered on the beam.
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The back of the S175C housing is engraved with the sensor specifications and a target for centering the beam on the sensor.
The S175C Microscope Slide Power Meter Thermal Sensor Head is designed to fit in the microscope slide holders of standard upright and inverted microscopes to measure the power at the sample plane. The large-active-area 18 mm x 18 mm sensor is protected by a glass plate, allowing immersion media to be applied. With a <2 s response time , 100 µW to 2 W optical power range, and 10 µW resolution, this thermal sensor is suited for high-power measurements of broadband sources, such as LEDs or white light illumination.
Please be aware that thermal sensors are sensitive to air vents and strong ambient temperature changes. Measurements should be taken once the sensor has settled to the ambient temperature.
Our most popular power meter consoles are included here for convenience. The PM100D digital power meter console features a back-lit LED screen and includes a 1 GB external SD memory card. The PM400 touch screen power meter console can perform the same functions as the PM100D with added features that include storing past power measurements in its 4 GB internal memory, inputs for external temperature and humidity sensors, programmable GPIO ports, and a capacitive touchscreen display that allows the unit to be operated with multi-touch gestures. Additionally, the PM400 allows optical power measurement data, temperature logs, spectral correction curves, and attenuation correction data can be saved by the user and transfered between the console and an external device for further analysis. These functions are particularly useful for tracking the consistency of the power at the sample plane over time.
For more information, click on the part number in the table below to view the complete presentation for each power meter console. The S170C and S175C sensors are also compatible with the PM100USB, PM200, and the PM320E consoles.