Laser Laser CommunicationsCommunications

Laser ClassesLaser Classes

Class I – Sealed systemsClass I – Sealed systems Class II – Output <1mWClass II – Output <1mW Class IIIa – Output 1mW - 5mWClass IIIa – Output 1mW - 5mW Class IIIb – Output 5mW – 500mWClass IIIb – Output 5mW – 500mW

Harmful to eyes, diffuse viewing OKHarmful to eyes, diffuse viewing OK Class IV – Output >500mWClass IV – Output >500mW

Harmful to skin and eyes, diffuse Harmful to skin and eyes, diffuse viewing hazardousviewing hazardous

Diode LasersDiode Lasers

Laser diodes emit an elliptical beam Laser diodes emit an elliptical beam with astigmatismwith astigmatism

Better units will include corrective Better units will include corrective lenses for astigmatism and to make lenses for astigmatism and to make the dot appear roundthe dot appear round

Neither of these problems are Neither of these problems are inherently bad for DX purposes but inherently bad for DX purposes but correcting them also improves correcting them also improves divergence, a big win (more gain).divergence, a big win (more gain).

Human Spectral Human Spectral ResponseResponse

Perceived IntensitiesPerceived Intensities

WavelengthWavelength MultiplierMultiplier ColorColor

532 nm532 nm 2828 GreenGreen

635 nm635 nm 77 Red-OrangeRed-Orange

640 nm640 nm 55 Red-OrangeRed-Orange

650 nm650 nm 33 RedRed

660 nm660 nm 22 RedRed

670 nm670 nm 11 RedRed

Laser DiodeLaser Diode

Laser Diodes include Photodiodes for feedback to insure consistent output

Pointer DesignPointer Design

Pointer InnardsPointer Innards

ModulationModulation

AMAM Easy with gas lasers, hard with diodesEasy with gas lasers, hard with diodes

PWM (Pulse Width Modulation)PWM (Pulse Width Modulation) Used by Ramsey in their kitUsed by Ramsey in their kit

PFM (Pulsed FM)PFM (Pulsed FM) Potentially the highest bandwidth Potentially the highest bandwidth

(>100kHz)(>100kHz)

Gain SystemsGain Systems

TransmitterTransmitter Maximum output Maximum output

powerpower Minimum divergenceMinimum divergence

ReceiverReceiver Maximum lens areaMaximum lens area ClarityClarity Tight focus on Tight focus on

detectordetector

FiltersFilters

Sun shade over detectorSun shade over detector Shade in front of lensShade in front of lens Detector spectral responseDetector spectral response Colored filtersColored filters

Absorb ~50% of available lightAbsorb ~50% of available light Difficult to find exact frequencyDifficult to find exact frequency

Mounting SystemsMounting Systems Mounts and stands need only be as accurate as Mounts and stands need only be as accurate as

beam divergencebeam divergence Good laser diodes will be 1-2mR (milliRadian)Good laser diodes will be 1-2mR (milliRadian) A 32 pitch screw at the end of a 2' mount will yield A 32 pitch screw at the end of a 2' mount will yield

1mR per revolution. Since quarter turns (even 1mR per revolution. Since quarter turns (even eighth turns) are possible, this is more than eighth turns) are possible, this is more than accurate enough accurate enough

Higher thread pitches allow shorter mounts which Higher thread pitches allow shorter mounts which may be more stable (against wind, vibration, may be more stable (against wind, vibration, wires)wires)

1mR is 1.5' of divergence every 1000', 3' at 2000 ', 1mR is 1.5' of divergence every 1000', 3' at 2000 ', etc.etc.

PointingPointing

GPS and CompassGPS and Compass Scopes and BinocularsScopes and Binoculars Strobe lights, large handheld floods, Strobe lights, large handheld floods,

headlightsheadlights HTs to yell when laser light is seen HTs to yell when laser light is seen

at remote locationat remote location

Weak Signal ModesWeak Signal Modes

Laser DXLaser DX

1991 - June 08 - 1991 - June 08 - WA7LYI and KY7B - WA7LYI and KY7B - 153.97 miles ! 153.97 miles !

Equipment used: 18 Equipment used: 18 inch fresnel lens into inch fresnel lens into Photomultiplier tubePhotomultiplier tube

Transmitter: 15 mw Transmitter: 15 mw helium cadmium laser helium cadmium laser (442 nm)(442 nm)

ApplicationsApplications

Transmit voice for miles line-of-sightTransmit voice for miles line-of-sight Use weak signal modes for “cloud Use weak signal modes for “cloud

scatter”scatter” Transmit video with cheap pensTransmit video with cheap pens Transmit high speed data without Transmit high speed data without

WEPWEP Blind flies for easy exterminationBlind flies for easy extermination