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Microscope PMT Photometers Hardware

 
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The OBB PMT Photometer consists of the following main elements

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Light tight C-mount photometer arm
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Adjustable viewing/targeting iris with parfocal eyepiece
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View/detect flipping mirror
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One, two or three PMT detection channels
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Dichroic cube/filter holders for dual or triple channel photometers
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High voltage, time constant, gain and signal output adjustments for each PMT housing

 

 

Single Channel Photometer Dual Channel Photometer Tri-Channel Photometer

Single Channel Photometer

Dual Channel Photometer

Tri-Channel Photometer

Adjustable Photometer Aperture

The photometer is equipped with an eyepiece which is positioned after the bilaterally adjustable vertical and horizontal slits for selecting the field of detection. This allows the user to directly view and adjust the same field of view that the detector sees.

The eyepiece is parfocal with the microscope field of view and has no magnification, so that the entire field that you see through the microscope eyepieces is the same as the one you see in the photometer eyepiece. By adjusting the four edges of the bilateral slit controls you are effectively creating any sized rectangle, slit or square within the field of view. This targeting area can be anywhere from as large as the entire field of view for an average response from a few or many cells, to as small as a few microns (depending on the microscope objective) to provide intracellular measurements.

   Entire cell selected with iris

Sub cellular region selected with iris

Backlit LED Option

The standard viewing eyepiece can be replaced with an optional backlighting LED to allow the user to set regions of interests without ever needing to move from the microscopes eyepiece. 

With this option the LED then illuminates the field of view through the adjustable iris. You can then look at the field of view through the microscope eyepieces and adjust the LED lit square or rectangle with the edges of the targeting iris.

Adjustable Pinhole (Optional)

For some applications like single molecule detection you may need to detect from precisely known physical areas in the field of view. For such applications having a variable iris is not sufficient, so OBB has an optional pinhole insert that replaces the adjustable iris

The pinhole assembly is a mechanical insert that goes in place of our standard aperture blade assembly. There is a one-inch diameter holder for laser cut pinhole apertures with holes that can be selected from 5 µm to 200 µm in diameter (select from list). The pinholes are positioned in the focal plane of the microscope and can be translated +/- 3 mm from center with easy to use micrometers.

Pinhole Option

Since the pinholes are so small in diameter, the only way to target through them is by backlighting the pinhole with our backlit LED option and visually aligning them in the field of view through the eyepieces of the microscope. The user can target a specific region of interest for the photometer to measure by using the X/Y translation on the pinhole insert or by moving the stage of the microscope.

Wavelength Selection

The photomultiplier tubes (PMT’s) used in the OBB microscope photometer can detect very low levels of light anywhere from 185 to 650 nm (or to 900 nm with optional red extended PMT). There are a number of ways that customers can determine what wavelength will be detected by the PMT for a given application. For the most part customers use bandpass filters, but occasionally long pass filters are also used to collect more light.

Single channel wavelength detection

For single channel photometers used in fluorescence microscopy, you would typically have a barrier emission filter on the dichroic cube that is positioned under the objective (in the case of an inverted fluorescence microscope). The barrier emission filter passes only a select band of emission wavelengths from all of the emission wavelengths there may be above the dichroic mirror’s transition wavelength. However, you could also have no barrier emission filter on the dichroic cube and instead use the standard 1” round filter holder that is positioned immediately in front of the PMT housing on the photometer arm. Since the OBB photometer is light tight there is no operational or performance difference in choosing either of these two filter positions.

Dual channel wavelength detection

Photometer dichroic cube mount

For dual channel photometers, the two PMT’s are intended to measure from two different wavelengths simultaneously. Therefore you will need to use no barrier emission filter on the microscopes dichroic cube assembly so that all emission wavelengths (above the dichroic mirror’s transition wavelength) are directed to the photometer. For these dual channel photometers, there is an optional dichroic cube holder plate that positions a detection dichroic cube assembly at the right angle intersection between the two PMT’s.

This photometer dichroic assembly would have no “entrance” filter since we want all of the emission wavelengths to be split by the dichroic mirror. The dichroic mirror’s transition wavelength is selected to be in between the two emission wavelengths that the experiment requires for detection. For selection of the two emission wavelengths you have the option of putting them on the two emission ports on the photometer dichroic cube, or in the filter holders positioned immediately in front of the PMT housings.

The multi channel OBB microscope photometers are designed to hold standard 18mm dichroic cubes, with 18 mm circular bandpass filters and an 18 x 26 mm dichroic mirror. Currently we offer three standard application specific dual emission cube assemblies that include two emission filters and an appropriate dichroic mirror. Custom filters and dichroics may be purchased separately.

Light path for photometer dichroic cube assembly

Triple channel wavelength detection

The triple channel photometer assembly detects light in a very similar way to the dual channel photometer except that we add a third PMT housing and a second photometer dichroic assembly.

Dual Mode, Analog/Photon Counting Photomultiplier Detection System(s)

The photomultiplier tubes (PMT’s) used in the OBB microscope photometer can detect very low levels of light anywhere from 185 to 650 nm (or 185 to 900 nm depending on the PMT selected).

For spectroscopy and microscopy experiments in the UV/Vis/NIR region of the spectrum, a photomultiplier tube (PMT) is the ideal detector for quantitative low light level measurements. A PMT is extremely sensitive, with very wide dynamic range so it can also measure high levels of light. PMT’s are also very fast so rapid changes in optical signals can be reliably monitored. As a practical matter, PMTs are durable, long-lived, and economical.

The OBB microscope photometer uses a self contained PMT housing that operates in either analog or photon counting modes with the flick of a switch. This ambient PMT housing is ideal for standard side-on PMTs that are used from 185 to 900 nanometers. It has a very low dark count for a non-cooled PMT housing providing a dark count of only ~ 50 to 500 counts per second (cps) depending on the PMT selected.

PMT's are better than photodiodes and APD's for low light detection

Although the quantum efficiency (QE) of a PMT is less than that of a silicon photodiode or avalanche photodiode (APD), a PMT has a much lower limit of low light detection due to the high current amplification (~ 107) of the electron multiplier in the PMT. It is because of this large gain and low noise that a PMT provides significantly better low light sensitivity than a photodiode or APD.

The OBB ambient PMT housing includes the following

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On/off switch
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Complete analog and photon counting circuitry
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Analog or photon counting mode/output switch
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Line voltage power supply
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High voltage power supply
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LCD display of PMT high voltage or measured analog signal
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Signal out BNC connection
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High voltage adjustment knob
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External high voltage control input BNC connection (for optional external control)
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RF shielded case for use inside Faraday cages
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Internal socket for most 1 1/8-inch side-on photomultiplier tubes

OBB’s photomultiplier detection system is very convenient and easy to use. It is built as a complete unit using modern design techniques and components. Everything needed to quantitate the intensity of light is packaged into a compact, attractive housing that attaches conveniently to your experiment. There are no unsightly boxes for power supplies or a multitude of cables tangled on your bench-top. The system incorporates a high voltage supply, all detector electronics, and the controls in a compact, attractive housing that also contains the PMT. You have a choice of standard PMTs to choose from or you can select from any other 1 1/8-inch side-on photomultiplier tubes that operate from -200 to -1,100 Volts DC. The PMT high voltage is shown on a digital display on the housing or you can select to show the actual analog signal from the PMT with just a flip of a switch. The high voltage can be adjusting manually or controlled externally with a signal at the “External Voltage Control” BNC. Power is delivered from an external AC adapter that is included.

Photomultiplier Tubes

PMTOBB’s ambient PMT housing will accept a wide variety of side-on 1 1/8-inch diameter photomultiplier tubes that operate from -200 to -1,100 Volts DC. It is optimized for PMTs with uniform dynode chains. PMTs are normally selected based on their wavelength response and their noise and/or sensitivity characteristics. Below are details for two of the most commonly selected PMTs offered as standard selections for use with our PMT housing. We can and do offer other special PMTs for custom applications.

 

 

185 to 650 photon counting or analog PMT

    Specifications

    Spectral Response 185 to 650 nm
    Photocathode Material Multialkali
    Effective Area of PMT 8 x 24 mm
    Supply Voltage 1250 V dc
    Cathode Sensitivity
    Quantum Efficiency at 300 nm (Peak)
    Luminous
    Radiant 400 nm (Peak)

    19 % typ.
    60 µA/lm typ.
    60 mA/W typ.
    Anode Sensitivity (at 1000 V)
    Luminous
    Radiant at 400 nm

    400 A/lm typ.
    4 x 105 A/W typ.
    Gain 6.7 x 105 typ.
    Anode Dark Current
    (After 30minute Storage in the darkness)
    0.1 nA

     

    185 to 900 photon counting or analog PMT

    Specifications

    Spectral Response 185 to 900 nm
    Photocathode Material Multialkali
    Effective Area of PMT 8 x 24 mm
    Supply Voltage 1250 V dc
    Cathode Sensitivity
    Quantum Efficiency at 260 nm (Peak)
    Luminous
    Radiant 400 nm

    25.4 % typ.
    250 µA/lm typ.
    74 mA/W typ.
    Anode Sensitivity
    Luminous
    Radiant at 400 nm

    2500 A/lm typ.
    7.4 x 105 A/W typ.
    Gain 1 x 105 typ.
    Anode Dark Current
    (After 30minute Storage in the darkness)
    3 nA

     

 
OBB has a policy of continuous product development and reserves the right to amend part numbers, descriptions and specifications without prior notice.
 
 

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HORIBA Scientific
Optical Building Blocks
3880 Park Avenue
Edison New Jersey
08820-3097

Tel: 732-494-8660
Fax: 732-623-8129
E-mail:info.sci@horiba.com