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Hinds Instruments PEM-CSC User Manual

Photoelastic modulator
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PEM-CSC
PHOTOELASTIC MODULATOR
USER MANUAL
Hinds Instruments, Inc.
P/N: 010-0000-114 UM Rev B

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  • Page 1 PEM-CSC PHOTOELASTIC MODULATOR USER MANUAL Hinds Instruments, Inc. P/N: 010-0000-114 UM Rev B...
  • Page 2 Information furnished by Hinds Instruments, Inc. is believed to be accurate and reliable; however, no responsibility is assumed by Hinds Instruments, Inc. for its use; nor for any infringements of patents or other rights of third parties which may result from its use.
  • Page 3 CAUTION! DO NOT turn on your modulator unless the optical head and the electronic head are connected by the head-to-head interconnect cable. SERIOUS DAMAGE MAY RESULT!

  • Page 5: Table Of Contents

    Overview ......................10 2 PEM-CSC Controller ....................11 PEM-CSC Controller Front Panel ............... 11 PEM-CSC Controller Front Panel Buttons ................ 11 PEM-CSC Controller Rear Panel ................ 12 PEM-CSC Controller Rear Panel Connections ..............12 3 Modulator Head Assembly ..................13 Optical Head ......................
  • Page 6 Recommended Optics Cleaning Solutions ............... 38 Cleaning the Optics ......................38 A Calibration........................ 41 PEM CSC Calibration ..................41 Calibration Theory ....................42 Light Sources for Modulator Calibration ............43 Calibration Using an Oscilloscope ..............44 Multiple Reflection Techniques ................. 47 Static Waveplate Techniques ................

  • Page 7: Operators' Safety Summary

    PEM-CSC Controller Labels The serial number, user safety warning, and CE certification labels are located on the PEM-CSC Controller rear panel. DC Power Supply This product is intended to operate from a DC power supply at 48 VDC. The main power input is 100 - 240VAC, 50/60 Hz, 1.4A.

  • Page 8: Do Not Operate Without Cover

    Do Not Operate Without Cover To avoid personal injury, do not operate the PEM-CSC Controller without the cover. Ensure the controller ventilation openings located on the top and bottom of the enclosure are clear of any obstructions. PEM CSC User Manual...

  • Page 9: Unpacking The Pem Csc

    A return authorization number (RMA) will be assigned to you. See Overview of the PEM CSC Help System on page 58 for further contact information. 7. Return approved items to Hinds Instruments Inc. at the following address: Hinds Instruments, Inc. 7245 NE Evergreen Pkwy Hillsboro, OR 97124-5850 8.

  • Page 10: Unpacking The Pem Optical Head

    Unpacking the PEM Optical Head CAUTION PLEASE USE CARE when unpacking the PEM optical head, for this assembly is very fragile. Please follow the unpacking instructions carefully. Unless this is done, the PEM system will not operate and the optical head may be irreversibly damaged. Special Instructions for I/FS50 Optical Head The following unpacking instructions are for an I/FS50 PEM optical head.

  • Page 11: Special Instructions For Series Ii Optical Heads

    Special Instructions for Series II Optical Heads Included in all orders for Series II Optical Heads is a packet outlining instructions for removing the Transducer Safety Clip.  A Phillips screwdriver has been included in the packet for removal of the outer lid of the optical enclosure ...

  • Page 12: Series Ii Zs50 & Zs42 Optical Heads

    1. Remove the 4 lids screws using the provided screwdriver. 2. Gently pull yellow clip out. Grab the provided tabs on the lower half of the clip. There is a split in the clip under the transducer. Separate the clip and lift it out from around the transducer.

  • Page 13: Series Ii Zs37 Optical Heads

    NOTE: DO NOT TURN OPTICAL HEAD OVER WHILE LID IS OFF – OPTICS WILL FALL OUT 3. Replace lid. Extra screws are provided. Series II ZS37 Optical Heads Split Unpacking II/ZS37 Optical Head 1. Remove the 4 lids screws using the provided screwdriver. 2.

  • Page 14: Introduction

    Introduction Overview The PEM CSC Photoelastic Modulator is an instrument used for modulating or varying (at a fixed frequency) the polarization of a beam of light. Hinds photoelastic modulators are used for measurement of circular and linear dichroism, birefringence, optical rotation, ellipsometry, polarimetry, reflection difference spectroscopy and FTIR double modulation.

  • Page 15: Pem-Csc Controller

    If the limit is enabled, check all connections between controller, electronic head and optical head. If the head-to-head cables have been disconnected, please contact Hinds Instruments. If the unit is recovered, re-initialize the controller to PC connection.  Data LED: The data LED will flash yellow whenever data is being sent to or from the controller over USB.

  • Page 16: Pem-Csc Controller Rear Panel

    PEM-CSC Controller Rear Panel PEM-CSC Rear Panel PEM-CSC Controller Rear Panel Connections  1f Output: BNC female connector provides TTL output of PEM, first harmonic frequency.  2f Output: BNC female connector provides TTL output of PEM, second harmonic frequency.

  • Page 17: Modulator Head Assembly

    Modulator Head Assembly The transducer-optical element assembly (called the “optical assembly”) is the heart of a PEM CSC photoelastic modulator. It consists of a rectangular or octagonal “window” of optical material bonded to a quartz piezoelectric transducer. Both optical element and transducer are tuned to the same frequency. When connected to a driver circuit, this assembly oscillates and produces the time-varying birefringence which is the basis of operation of the PEM.

  • Page 18: Model Ii/Fs42, 47, 50 Optical Head Dimensions

    Model II/FS42, 47, 50 Optical Head Dimensions Model II/FS50, 60 Optical Head Dimensions PEM CSC User Manual...

  • Page 19: Model Ii/Zs37, 42, 50 Optical Head Dimensions

    Model II/ZS37, 42, 50 Optical Head Dimensions Model II/FS74, 84 Optical Head Dimensions...

  • Page 20: Electronic Head

    The optical head is connected to the electronic driver circuit (housed in the “electronic head”) by head-to-head interconnect SMA cables. This assembly of the optical head, the electronic head, and the head-to-head interconnect cables comprises the “modulator head,” which should be regarded as a single unit. CAUTION Operation of the electronic head without the head-to-head cables and optical head connected should never be attempted.

  • Page 21: Initial Set-Up

    Initial Set-Up Before initial set-up, the PEM optic head should be unpackaged as described in Unpacking the PEM Optical Head on page 6. Connecting the PEM Optical and Electronic Heads There are two different connection configurations between the optical head and electronic head based upon the type of optical head used.
  • Page 22 Connecting I/FS50 Optical Head to Electronic Head Connect the black SMA Head-to-Head Interconnect cables provided. Please note that the optical head receives the RP SMA connection. Connecting II/ZS50 Optical Head to Electronic Head PEM CSC User Manual...
  • Page 23 Connecting II/ZS50 Optical Head to Electronic Head (Cross Connection) 2. Connect the electronic head to the PEM-CSC Controller using the Controller-to- Head cable. 3. Connect the power to the PEM-CSC Controller using the 48V power supply. 4. Connect the USB cable to the computer.

  • Page 24: Optical Bench Set-Up

    Optical Bench Set-up The optical bench and electronic configuration depend on the particular application required for the modulator. More detailed set-up information can be found at our website http://www.hindsinstruments.com/applications for an applications pull down menu. The most common optical and electronic setup for checkout and calibration of the modulator is shown in the figure below.
  • Page 25 The detector circuitry deserves some special comment. Care must be taken to ensure adequate frequency response, typically several times the PEM operating frequency. Pre-amplified photo detectors are available from Hinds Instruments that fit this need. See page 58 for contacting Hinds Instruments Inc.

  • Page 26: Pem Control Software

    Instruments for assistance with Windows 7. To begin installation, first download the software installer from https://www.hindsinstruments.com/products/photoelastic-modulators/PEM-CSC/. Download this package on the computer that the PEM CSC will be connected to (Local Computer). After the download has completed, right click on the .zip file and select ‘Extract All…’...

  • Page 27: Setup Running

    Once complete, the set up will prompt you to select ‘Finish’, indicating the software has been successfully installed on the computer. PEM-CSC Software Installer, Finish The PEM Control Software is now installed. There will be a shortcut placed on your...

  • Page 28: Pem Csc Control Software

    PEM CSC Control Software PEM Control Software allows the user to remotely operate the PEM-CSC controller from a PC. This section provides an overview of PEM Control Software installation and the remote operation of the PEM-CSC Controller. Setup of the PEM-CSC Controller for Use with PEM Control...
  • Page 29 3. Use the dropdown to select the computer COM port number used by the PEM CSC Controller, then press ‘OK’ to open the main window. Main Interface: Main Display Screen When launching the PEM Control Software, the main display screen will appear with the default settings as shown. This screen allows for adjustments to wavelength and retardation settings as well as provides an update for the resonant frequency.
  • Page 30 1. Double click the retardation displayed to highlight the setting and then enter a new retardation using the keyboard. 2. Click on the up▲ or down▼ arrow to the right of the retardation display to adjust the retardation setting by single digits. Retardation Units: The retardation units field displays the selected retardation unit.
  • Page 31 Step Increment: Step increment describes the step size of a wavelength sweep. Entering a different step increment can be accomplished two ways: 1. Double click the step increment displayed to highlight the setting and then enter a new step increment using the keyboard. 2.
  • Page 32 for unique experiments or software where the user will communicate through the serial port. Select the view tab and select ‘Show Debug Panel’ to open the debug panel on the window. PEM CSC User Manual...
  • Page 33 Themes The PEM Control Software offers both a light and dark theme. Select the view tab and select ‘Use Light/Dark Theme’ to switch themes.
  • Page 34 Change COM port Select the settings tab and select ‘Serial Port’ to change the COM port number to the PEM CSC Controller. The serial port dialog box will appear. Use the dropdown to select the appropriate COM port. PEM CSC User Manual...

  • Page 35: Communication Protocol

    PEM-CSC connects to the computer as a USB serial COM port. The connection baud rate is 250,000 bytes per second. As this is a USB serial port, the software defined baud rate can be set anywhere from 9,600 to 250,000 and the PEM-CSC should still communicate.
  • Page 36 Arguments can also be a simple integer (e.g 1). Arguments may take a vector format of more than one argument. For these cases, individual values are separated by a comma,’,’. Please allow 300ms for PEM-CSC to return after a command is sent. Command structure overview. Command...
  • Page 37 :DRiVe? Get modulator drive voltage as range o to 1 :AMPlitude Set modulator amplitude in nanometers or retardance :AMPlitude? Get modulator amplitude in nanometers of retardance :AMPRange? Get modulator retardation amplitude range from lowest to highest in nanometers :FREQuency? Get modulation frequency in Hz :STABLE? Get modulator stability :SYStem...
  • Page 38 Short :MOD:DRV # command Type Get/Set Purpose Sets the voltage to the modulator on an arbitrary range of 0.0 (lowest modulation amplitude) to 1.0 (highest modulation amplitude) Input example :MOD:DRV 0.1325 Output [DRIVE](1.325000E-1) example Command :MODulator:AMPlitude # Short :MOD:AMP # command Type Get/Set...
  • Page 39 Command :MODulator:FREQuency? Short :MOD:FREQ? command Type Purpose Reports the frequency of modulation in Hz Input example :MOD:FREQ? Output [FREQUENCY](5.01930899E+4) example Command :MODulator:STABLE? Short :MOD:STABLE? command Type Purpose Returns if the PEM is stable (binary) Input example :MOD:STABLE? Output [STABLE](1) example Command : SYStem:PEMOutput # Short...

  • Page 40: Troubleshooting

    Ensure the optical head is disconnected from any SMA cables before removing cover. High voltages can be present otherwise. Do not remove cover from PEM-CSC Controller unless instructed to and being supported by Hinds Instruments personnel. PEM CSC User Manual...

  • Page 41: Maintenance

    Maintenance Calibration PEM CSC modulators are calibrated at the factory before shipment. For most applications, recalibration is neither necessary nor appropriate. For a few applications, however, an on-site calibration procedure will be necessary if optimum performance is to be achieved. Hinds’ engineers will be glad to advise users on whether on site calibration is appropriate in a particular case.

  • Page 42: Cleaning

    The PEM units are rugged and reliable and normally require no additional maintenance. If trouble occurs, please consult the troubleshooting section and then contact Hinds’ engineers for assistance. Cleaning When the PEM was shipped, the surface was clean and defect free; however, the rigors of packing and shipping may leave some residue on the optical surface(s).
  • Page 43 To guard against electrical shock or instrument damage, never allow water to get inside the case. Unplug the unit before cleaning the optics. Cotton Swab Method Using a 100% cotton swab moistened with solvent, wipe the surface gently while rotating the swab slowly. This action ensures that the contaminants are lifted away from the surface of the optic.
  • Page 44 2. Using the recommended cleaning agent, soak the lens tissue until the entire surface is damp (not wet). 3. Grasp two free corners of the lens tissue and drag the tissue across the surface away from the junction in a smooth, even manner so the alcohol dries immediately as the rear edge of the tissue moves over the optical surface.

  • Page 45: A Calibration

    Calibration by Theodore Oakberg, PhD Proper retardation calibration of photoelastic modulator systems is essential for optimum performance. This is best accomplished with the modulator in the optical setup in which it will be used. This application note is intended to assist users with in situ calibration of their PEMs.

  • Page 46: Calibration Theory

    Calibration Theory The optical setup for most calibration procedures is shown in the figure below. Modulator Polarizer 0° Monochromatic Detector Light Source +45° Polarizer W aveplate 0° -45° (Some experiments) Typical Optical Setup The modulator is placed between crossed polarizers, each of which is oriented with its passing axis at 45 degrees with respect to the modulator axis.

  • Page 47: Light Sources For Modulator Calibration

    The procedures described below for PEM calibration each require a monochromatic light source. A brief discussion of light sources suitable for this purpose is in order. Lasers are excellent sources of monochromatic light. At Hinds Instruments, we use HeNe lasers to calibrate most PEMs which we manufacture. Laser beams are intense and well collimated, and do not normally require any focusing optics in the calibration optical setup.

  • Page 48: Calibration Using An Oscilloscope

    Calibration Using an Oscilloscope The most straightforward procedure, and the one used at Hinds Instruments for the factory calibration of modulators, utilizes a monochromatic light source (e.g. HeNe laser), a solid state detector (e.g. silicon photodiode), and an oscilloscope. A block diagram for the setup is given in the figure below.
  • Page 49 Figure 3. W aveform for Half-w ave Retardation Waveform for Half-wave Retardation Note the flat top of the peaks. (Depending on the precise optical and electronic configurations, this display might appear inverted.) This feature is very distinctive, and by adjusting the retardation at half-wave to give the above waveform an accuracy of better than 1% can be achieved.
  • Page 50 Figure 5. Retardation 100% of Half-w ave Retardation 110% of Half-wave For retardation values of multiple half-waves, the intensity functions continue to exhibit the “flat topped” (or “flat bottomed”) characteristic which is useful for calibration. The waveform for a retardation of four half-waves is shown in the figure above. Figure 6.

  • Page 51: Multiple Reflection Techniques

    Multiple Reflection Techniques Precise setting of the modulator peak retardation at levels less than half wave may be done by several different methods. For integral fractions of a half-wave, the oscilloscope technique described above may be used by arranging the optical system so that the light beam traverses the center of the modulator multiple times.

  • Page 52: Bessel Function Zero Methods

    Bessel Function Zero Methods An examination of equation 2 suggests a method for precise setting of certain values of retardation. Note, for example, the “DC” term in equation 2. For certain values of A (e.g. 2.405    radians), , and therefore the DC term becomes a constant, independent of the birefringence B.

  • Page 53: Bessel Function Ratio Methods

    Addition of a birefringent element so that a significant 1f signal at the modulator frequency is obtained, will enable determining the controller setting for which     . (This occurs for radians.) Detection of the null point is made with a lock-in amplifier at the modulator frequency.

  • Page 54: Parallel Polarizer Calibration At A Single Wavelength

    A sample calculation is given below for quarter-wave retardation. The required Bessel functions are:     For half-wave:     For quarter wave: The required setting for quarter-wave retardation is:       ...
  • Page 55 Ratio V vs retardation, radians For low values of retardation, this ratio is approximately a constant! This means that use of this ratio for determining PEM retardation is quite insensitive. The situation may be corrected if the PEM is placed between parallel polarizers. this case: ...
  • Page 56 Ratio V vs. retardation (radians) for parallel polarizers This method gives monotonically increasing values of the ratio V for low values of A (3 radians and less). It lacks sensitivity for retardation values near 3.5 radians, but this is where the flat-topped half-wave waveform occurs (  radians). The graph is used in reverse, for a given value of may be determined.
  • Page 57 Another method would be to correct for 1) and 2) by blocking the light (near the light source, not near the detector) and recording the detector output voltage. This baseline value would then be subtracted from the measured value of DC volts to give V There is another problem which is more subtle, but just as important.

  • Page 58: B Specifications

    Specifications General- Controller Model Number Controller, PEM-CSC 6.585” W x 1.363” H x 9.383” D Size (167.28 mm x 3.463 mm x 238.34 mm) Weight 1.8 lbs. (0.82 kg) (without head assembly) Power Supply Output: 48VDC, 2A Input: 100-240VAC, 50/60Hz, 1.4A...

  • Page 59: Environmental

    See ‘Optical Head Specifications’ Output Frequency ‘f’, 50% +/- 0.1% Phase Stability Duty Cycle ‘2f’, 50% +/- 0.1% USB Connection USB 2.0 Type B (Male – Male) Connector Style Environmental Designed for indoor use only. Operating Temperature 2 to +50 degrees C (36 to 122 degrees F) Storage Temperature -40 to +65 degrees C (-40 to 150 degrees F)

  • Page 60: C Optical Head Specifications

    Optical Head Specifications Model Optical Nominal Retardation Range Useful Material Frequency Aperture Quarter Wave Half Wave 170 nm – 2 µm 170 nm – 1 µm I/FS50 Fused Silica 50 kHz 16 mm 170 nm – 2 µm 170 nm – 1 µm I/FS20 Fused Silica 20 kHz...

  • Page 61: D User Support Information

    User Support Information Hinds Instruments makes every attempt to ensure that the instruments we provide are products of superior quality and workmanship. We also aim to provide superior technical user support. If you have any questions, or if you encounter problems in the operation of your PEM instrument or system, please contact us.

  • Page 62: Overview Of The Pem Csc Help System

    Overview of the PEM CSC Help System As shown in the table below, you can contact Hinds Instruments, Inc. Technical Support in several ways. Method Information Monday - Friday 8:00 AM to 4:00 PM PST Telephone (503) 690-2000 (503) 690-3000 Email support@hindsinstruments.com...

  • Page 63: Return For Repair Procedure

    Return For Repair Procedure If your unit ever does need repair, please contact Hinds Instruments, Inc. before attempting repairs yourself or returning it to us. We may be able to provide additional troubleshooting suggestions to help diagnose the problem. In the event it is necessary to return the unit to us, we will give it our prompt and professional attention.

  • Page 64: Return Shipping Address

    If the unit is not under warranty, we will contact you with an estimate of the charges. If you approve of the indicated repairs and cost, Hinds Instruments, Inc. will return your repaired unit after all charges (including parts, labor and return shipping and handling) have been paid.
  • Page 65 PEM CSC User Manual...

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