tecoptics fpi-25 fabry-perot interferometer with fpz-3 ramp

Download TecOptics FPI-25 Fabry-Perot Interferometer with FPZ-3 Ramp

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  • Technical Optics Ltd.

    FPI-25 Fabry-Perot Interferometer

    with

    FPZ-3 Ramp Generator

    Operation Instructions

  • Page 1

    1 INTRODUCTION....................................................................................................................... 2

    2 SPECIFICATIONS.................................................................................................................... 4 RAMP GENERATOR ...............................................................................................................................................4 OPTICAL HEAD .....................................................................................................................................................4

    3 SYSTEM DESCRIPTION AND CONTROLS ............................................................................ 6 FPI-25 OPTICAL HEAD..........................................................................................................................................6 FP-3 RAMP GENERATOR.......................................................................................................................................8 CONTROL FUNCTIONS ...........................................................................................................................................8 INPUT/OUTPUT SOCKETS ......................................................................................................................................9

    4 INSTALLATION AND OPERATION....................................................................................... 11 COMPONENT CHECKLIST.....................................................................................................................................11 CHOICE OF OPERATING SITE ...............................................................................................................................11 INSERTING THE MIRRORS ....................................................................................................................................11 ELECTRICAL CONNECTIONS.................................................................................................................................12 ALIGNMENT OF THE OPTICAL HEAD......................................................................................................................13 ADJUSTMENT OF THE MIRROR SPACING ...............................................................................................................14 CALIBRATION OF THE MIRROR SPACING ................................................................................................................14

    5 UNDERSTANDING THE DISPLAY ........................................................................................ 16

    APPENDIX: FABRY-PEROT ETALON THEORY ..................................................................... 19 THE PLANAR FABRY-PEROT ................................................................................................................................19 THE CONFOCAL FABRY-PEROT............................................................................................................................22 DEFECTS AND THEIR EFFECT ON FINESSE IN PLANAR ETALONS ............................................................................24 REDUCTION IN TRANSMISSION .............................................................................................................................25 ABSORPTION IN COATINGS ..................................................................................................................................25 CHOOSING A FABRY-PEROT ................................................................................................................................27

  • Page 2

    1 Introduction The Technical Optics FPI-25 is a Fabry-Perot interferometer which can be scanned or tuned by means of piezo-electric transducers. The easily variable free spectral range makes the FPI-25 an extremely flexible laboratory tool, with a wide range of spectroscopic applications. The wide 25mm aperture means that even weak sources are not a problem, and the long integration times associated with many remote sensing applications can be reduced. The transducers are controlled by means of high voltage signals obtained from the FPZ-3RG ramp generator unit. The various drive signals provided by the FP-3RG allow the optical head to be used in various ways, making it a versatile spectroscopic instrument. The plate spacing can be ramped rapidly making the head useful for the real time spectral analysis of CW laser sources. When a slower ramp speed is employed a time-averaged spectrum of a pulsed laser may be obtained. If the plates are not ramped then the FPI-25 can be used as a tunable filter, which has excellent performance with regard to both bandwidth, and contrast ratio, making the device ideally suited to applications where high discrimination is needed.

    ELECTRICAL WARNING

    This system is designed to operate from either 110-125volts or 220-250volts AC power supply input.

    Do not attempt to operate the instrument until the voltage selector has been correctly set (see section 5).

    Failure to correctly configure the power input module may result in serious damage to the instrument.

    The high voltages delivered from the HV out socket on the interferometer controller are potentially very dangerous,

    and although completely safe in normal use, misuse could be hazardous.

    LASER SAFETY WARNING

  • Page 3

    This apparatus is normally used to filter the output from laser sources. The operator should be familiar with the

    appropriate laser safety procedures and regulations. In particular it should be noted that a portion of the laser beam

    incident on the optical head will be reflected. This can be hazardous, and both incident and reflected beams should

    be enclosed if necessary.

  • Page 4

    2 Specifications

    Ramp Generator

    Power Input

    Piezo-electric Controls - Bias

    Piezo-electric Controls - Ramp

    Dimensions

    Optical Head

    Optical Parameters

    VOLTAGE 110 - 125V or 220 - 250 FREQUENCY 50 - 60Hz POWER CONSUMPTION 120VA

    OFFSET 0 - 450V TILT 0 - 550V OUTPUT IMPEDANCE 1M

    RAMP EXTENT 0 - 1000V TRIM RANGE 0 - 15% of ramp extent RAMP RATE 0.01 - 100 V/ms FLYBACK RATE 100 V/ms DRIVE CAPABILITY 2.5mA per channel

    WIDTH 435mm DEPTH 265mm HEIGHT 100mm

  • Page 5

    Dimensions

    MODEL W1000 W2000 W3000 CLEAR APERTURE 25mm 25mm 25mm MINIMUM CAVITY SPACING 300GHz MINIMUM FSR 2.5GHz 1.5GHz 1GHz FINESSE dependent on mirrors and cavity configuration MIRROR RAMP RANGE 1.8m in LOW extension range - 6m in HIGH extension range MIRROR OFFSET RANGE 1.8m SCAN NON-LINEARITY < 5% nominal

    LENGTH 308mm 348mm 398mm HEIGHT 146mm WIDTH 120mm

  • Page 6

    3 System Description and Controls

    FPI-25 Optical Head

    Differential Screws

    Clamp Screws HV socket

    Cavity AdjustmentScrew

    Detector Focussing Unit

    Si or GePhotodiode

    Adjustable Base Unit

    Mirrors

    This, the most important component, houses the optics and the piezo-electric transducers which scan them. It consists of an Invar tri-bar structure supporting Invar endplates and body. A fine pitch differential screw assembly is attached to one end, in which one of the mirrors is mounted. This allows for coarse (in optical terms) adjustment of the parallelism of the interferometer (see section 4). The main body of the instrument, including the other mirror and the piezo-electric transducers, slides on the three bars. The mirror spacing can be readily varied by undoing the three clamp screws, turning the cavity adjustment screw, and then re-tightening the clamp screws (see section 4). The range over which the device can be scanned can be set to either LOW, suitable for working in the UV-VIS-NIR range, or HIGH for the IR region. The scanning range is selected by means of a toggle switch on the optical head. A detector focusing unit can be attached to the differential end of the interferometer, collecting light from the full 25mm aperture of the instrument, and focusing it onto a photodiode (either silicon or germanium).

  • Page 7

    The complete assembly is held on an adjustable base unit, allowing fine variations in the alignment to the optical source to be made.

  • Page 8

    FP-3 Ramp Generator

    TILT

    A B C

    MONITOR

    OFFSET

    BIAS

    TRIM

    A B C

    MONITOR

    SET VOLTS

    RAMP

    MAN SIN AUT EXT 1 3 10 30 100 100

    MODE RATE VOLTS PER mS

    CONTROL

    MONITOR INPUT BLANKING EXT EXT

    START

    RESET

    FUSE T1A POWER OUTPUT

    TECOPTICS FP-3-RG

    The FPZ-3 ramp generator provides all of the voltage signals necessary to control the FPI-25 optical head. There are six high voltages required, which are of two different types: Firstly there are three bias signals which set the high degree of parallelism required for successful operation of Fabry-Perot etalons, and also provide offset to allow the fringe peaks to be moved relative to the start of the ramp. Secondly there are three ramp signals which provide the scanning ability of the etalon. These ramp signals are individually trimmed to maintain the parallelism set by the bias signals. A full description of the controls and how they effect the voltages follows.

    Control Functions

    There are three banks of controls on the front of the FPZ-3 ramp generator. BIAS

    This single turn rotary control applies a common voltage signal to the stacks supporting the non-

    scanning mirror. This

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