[Laser] laser ratings

[Charles Pooley]

Diode lasers, like LEDs, should be driven from a current source.  The forward 
voltage is not well defined.  Lasers should not be over driven, as the failure 
mechanism is very fast.

Cheap pointers are typically 3 mw or so.  standard type diodes are available in 
near IR, visible from milliwatt to watt levels.  Above the threshold, the output 
follows the instantaneous current to very high frequencies.  In a comm system, 
bandwidth of modulation will be limited by the bandwidth of the receiver.

These diodes have a rectangular output with a slightly different position of 
light origination for the parallel and perpendicular to junction so a cylinder 
lens is needed to make the focus equal.

A type, VCSEL, has the cavity vertical and is axisymmetrical soi plain lensed 
can be used.  They are cheap, but have a low output--typ 1.5 mw, and 850 nm 
wavelength.  In near future 650 nm and somewhat higher output will become 
available.

Download some data sheets and you can get a general idea of the behavior.

Charles Pooley      KD6HKU     Microlaunchers




________________________________
From: James Whitfield <n5gui at cox.net>
To: laser at mailman.qth.net
Sent: Thu, July 22, 2010 8:39:51 PM
Subject: [Laser] laser ratings

Recent discussions about laser power have revealed a gap in my understanding of 
such things.

I have a laser pointer that I have been using for several years for demos and as 
the emitter element on an MCW transmitter.  The label says its maximum power 
output is 4 mWatt.  It is built for two AA batteries.  I measured the input 
voltage.  It seems noticeably weak at 2.5 volts and it draws 16 mA.  With 
fresher batteries, it seems full power using 2.8 volts drawing 33 mA.

With my MCW transmitter, I pulse it with about 30 mA at about 400 Hz, not 
bothering to try to control the voltage, just a hard current limit, pulsed or 
not.

The numbers say its input power is 40 mWatt for the weak condition, and over 90 
for the bright.  I am pretty sure that most of that power is actually going into 
the laser diode.  If the rating is output power, then the conversion efficiency 
seems to be less than 10%.  I suppose that is on par with an underdriven tube 
type class A amplifier.

Anyway, I was wondering if someone can explain the laser power rating system, or 
maybe provide a link where that information is available.

Thanks in advance.


James
n5gui

______________________________________________________________
Laser mailing list
Home: http://mailman.qth.net/mailman/listinfo/laser
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Laser at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html