Microscope Slide Power Meter Sensor Heads

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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.

Features

• Compatible with Standard Upright and Inverted Microscopes
• Designed to Measure Power at the Sample Plane
• Large 18 mm x 18 mm Active Sensor Area
• Low-Power Photodiode Sensor (Item # S170C)
  
  • Wavelength Range: 350 nm to 1100 nm
  • Sensitive to Optical Powers from 10 nW to 150 mW
• High-Power Thermal Sensor (Item # S175C)
  • Wavelength Range: 300 nm to 10.6 µm
  • Measure Optical Powers from 100 µW to 2 W
• Sensor Housing with the Same Footprint as Standard Microscope Slides: 76.0 mm x 25.2 mm
• Novel Optical Design to Accommodate High NA Objectives (See Optical Design Tab)
• Information Stored in Connector:
  • Sensor Data for Automatic Calibration when Using Thorlabs' Power Meter Consoles
    (Sold Separately Below)
  • NIST- and PTB-Traceable Calibration Data

Applications

• Measure Intensity of the Microscope Light Source at the Sample Plane
• Determine Transmission of a Fluorescence Filter Set
• Ensure Lighting Conditions are Consistent Between Experiments

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).

Day-to-Day Usage
The sensors support power measurements for objectives with NAs up to 1.45, and are usable in air and with water- or oil-based immersion media (see the Optical Design tab for details). As seen in the image above to the right, the back of the sensor is engraved with the recommended NA for air (<0.95), water (<1.30), and oil (<1.45) objectives. The active sensor area is protected by a glass cover surface, which can be easily cleaned using compressed air or using optic tissue moistened with acetone or methanol.

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
These power sensor heads are compatible with the PM100D, PM100A, PM100USB, PM200, PM400, and PM320E power meter consoles. The PM100A, PM100D, and PM400 consoles are sold below for convenience. As seen in the image to the left, a 1.5 m cable attached to the side of the sensor head leads to a D-sub 9-pin male connector. Sensor specifications for automated calibration and the NIST- and PTB-traceable calibration data are stored in non-volatile memory in the sensor connector and can be read out using compatible Thorlabs power meter consoles.

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 filter^a 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.)

1. Do not place immersion media directly on the ND filter of these photodiode sensors as it cannot be cleaned from the filter surface. The S170C is specifically designed for this application. The example used here is only intended to demonstrate the advantages of the S170C's optical design.