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# HomeBrew Science - RubyLaser: Optical Pumping -

Flash Lamps Considerations

Optical Pumping is the second critical step. Flashlamps used for laser pumping are usually expensive and hard to find.
Perkin Elmer  has a huge variety of flashlamps suitables for any kind of laser rods on his catalog, but the price is quite unattainable for the hobbist. On the other hand reliability and calculation of Pulse Formin Network are essential for industrial usage. It's up to you...

From my point of view, an array of four tipical xenon flashlamps of nominal energy of 250J, are good enough for my purpose.By the way, calculation of PFN has been a little tricky.

I spent lof and lot of time to understand electrical parameters of gas lamps. Fortunally there are some irreplaceable resorces on the Net. Sam's FAQ is the right place where you may fiind answer to any kind of technical question.

There also are a  section about flashlamps power supply calculation and usage.

Back to our point: the Optical Pump.

This laser uses 4 photo flashlamps model FT-218, manufacturer unknown.

Electrical parameters for FT218 flashlamps (from manufacturer)

Nominal Input Energy : 250J
Vmin                        : 350V
Vmax                       : 500V
Vtyp                         : 450V
envelope                   : quartz

That's all I got form the seller, a too few information to design a proper PFN.
So I decided to calculate the real charcteristics startin from the phisical diimensions. General Xenon Flash and Strobe Design Guidelines  gives the key to understand flashlamps.

Starting from the physical dimensions, is possible to get new electrical parameters.

Physical Dimensions of  FT218 flashlamps

Arc Lenght            (Larc)            : 160 mm
Internal Diameter   (ID)                : 6mm
Discharge Area     (Sarc)            : 3015 mm^2
Discharge Volume (Varc)            : 4420 mm^3
Cathode dimensions                   : l=3.5mm d=2mm

New Electrical parameters for FT218 flashlamps (calculated)

Maximun Input Energy        : 300J
Vmax                                 : 950V
Average Power (free-air)    : 100W
Average Resistance            : 2 ohms
Dinamic Resiastance  (Ko) : 24 ohm*sqr(A)

The estimated Electrical to Optical conversion is 50%, that means only the 50% of electrical energy is converted to light.

A simple Excel Sheet may be used to calculate FlashLamps electrical parameters and PFN Inductor and Capacitor.