Lasers convert electrical energy into light energy using a process called stimulated emission. High voltage electrical energy is used to energize a lasing gas mixture inside a resonator cavity. When the grid signal allows the electricity to pass through the electrodes, the gas becomes ionized and produces a controlled laser beam through optics. The RF tube, a triode oscillator, cycles the high voltage on and off using pulse width modulation to control the laser output power level.

1. LaserLASER
Electrical
Energy
Light
Energy
LASER BASICS
Lasers convert electrical energy into
light energy, not only visible light but
electromagnetic radiation of any
frequency, to perform work such as
welding, cutting material, heat
treatment, surgical procedures, etc.

2. Electrical
Energy
DC 11kV
5 Amps
Light
Energy
Electrodes
Ground
Resonator
Lasing
Gas
Switch
Open
LASER BASICS
High voltage / high current electrical
energy is used to pass across the
electrodes and energize the lasing
gas mixture.

3. Electrical
Energy
DC 11kV
5 Amps
Light
Energy
Electrodes
Ground
Resonator
Plasma
Energized
Grid
Control
When the grid signal allows the
electrical energy to pass across the
electrodes the lasing gas will become
energized into a gas plasma. This will
be converted through optics into a
controlled laser beam.
LASER BASICS

4. Grid
Control
Ground
Rofin
CPU
Filament
DC
Power
RLC
Circuit
Over
Current
Board
Rectifier
Bank
HV
XFMR
0
15
0
2.9
RF Tube
(Triode)
Oscillator
The RF tube, a Triode oscillator, is
used to cycle the High voltage on and
off to the electrodes inside the
resonator
LASER BASICS

5. DUTY CYCLE = 25%
PULSE WIDTH MODULATION
- -
-
25%
50%
75%
12V
25%
ON
75%
OFF
25%
ON
75%
OFF
25%
ON
75%
OFF
25%
ON
75%
OFF
12V3V
PWM DUTY CYCLE = 25%
Controlling a dc electric motor can be accomplished USING ANALOG CONTROL SUCH AS A
RHEOSTAT OR DIGITALLY BY USING PULSE WIDTH MODULATION (PWM)

6. DUTY CYCLE = 50%
- -
-
25%
50%
75%
12V
12V6V
PWM DUTY CYCLE = 50%
50%
ON
50%
OFF
50%
ON
50%
OFF
50%
ON
50%
OFF
50%
ON
50%
OFF
If we rotate the rheostat to 50% duty cycle the average voltage will now be 6V and more energy will
be supplied to the motor, increasing the motor’s output.
PULSE WIDTH MODULATION

7. DUTY CYCLE = 75%
- -
-
25%
50%
75%
12V
12V9V
PWM DUTY CYCLE = 75%
75%
ON
25%
OFF
75%
ON
25%
OFF
75%
ON
25%
OFF
75%
ON
25%
OFF
If we rotate the rheostat to 75% duty cycle the average voltage will now be 9V and more energy will
be supplied to the motor, increasing the motor’s output.
PULSE WIDTH MODULATION

8. DIGITAL PWM SIGNAL @ 10% DUTY CYCLE WOULD EQUATE TO A 1V ANALOG SIGNAL
10V
0V
10V
0V DIGITAL PWM SIGNAL @ 50% DUTY CYCLE WOULD EQUATE TO A 5V ANALOG SIGNAL
1V
5V
Any analog signal can be modulated by PWM. By cycling a digital signal off and on at a fast enough
rate, and with a certain duty cycle, the output will appear to behave like a constant voltage analog
signal
PULSE WIDTH MODULATION

9. PERIOD
12.5µS
DUTY CYCLE 10%
DUTY CYCLE 50%
DUTY CYCLE 75%
PULSE
WIDTH
PWM FREQUENCY – 80KHz (ƒ=1/T)
OFF TIME
toff
ON TIME
ton
The grid signal uses the pulse width modulation(PWM) technique for controlling the output of the RF
tube. PWM is a way of digitally encoding analog signal levels. The digital signal at any instant of time
is either fully on or fully off. The current is supplied to the RF tube by means of a repeating series of
on and off pulses. Any analog value can be encoded using PWM.
PULSE WIDTH MODULATION

10. When Benjamin Franklin made his speculation regarding the direction of charge flow (from the smooth wax to the
rough wool), he set a standard for electrical notation that exists to this day, despite the fact that we know electrons
are the basic units of charge, and that they are displaced from the wool to the wax -- not from the wax to the wool --
when those two substances are rubbed together. This is why electrons are said to have a negative charge: because
Franklin assumed electric charge moved in the opposite direction that it actually does, and so objects he called
"negative" (representing a deficiency of charge) actually have a surplus of electrons.
By the time the true direction of electron flow was discovered, the nomenclature of "positive" and "negative" had
already been so well established in the scientific community that no effort was made to change it, although calling
electrons "positive" would make more sense in referring to "excess" charge. The terms "positive" and "negative" are
human inventions, and as such have no absolute meaning beyond our own conventions of language and scientific
description. Franklin could have just as easily referred to a surplus of charge as "black" and a deficiency as "white,"
in which case scientists would speak of electrons having a "white" charge (assuming the same incorrect conjecture
of charge position between wax and wool)
.
However, because we tend to associate the word "positive" with "surplus" and "negative" with "deficiency," the
standard label for electron charge does seem backward. Because of this, many engineers decided to retain the old
concept of electricity with "positive" referring to a surplus of charge, and label charge flow (current) accordingly. This
became known as conventional flow notation:
CONVENTIONAL FLOW
NOTATION
Conventional Current Flow vs. Electron Flow

11. ELECTRON FLOW
NOTATION
Others chose to designate charge flow according to the actual motion of electrons in a circuit, from negative to
positive. This form of symbology became known as electron flow notation:
Using the electron flow convention will help in the understanding of how the RF tube operates.
When current is flowing in a wire, what is actually moving is the electrons. Electrons have negative charges.
Negative charge is usually shown in black, so in this illustration electrons are represented as little white minus signs
in little black circles. When they have the chance, electrons generally move from areas that are crowded with
electrons (negative charge) to areas that don't have as many electrons (positive charge).
Conventional Current Flow vs. Electron Flow

12. There really is something that moves from positive to negative while the electrons are moving the other way.
The hole that the electron leaves behind as it moves toward the positive charge can be thought of as moving
toward the negative charge.
The large circles in the illustration below represent atoms, with positive charges in the middle and negative
electrons around the outside. When the electron is in the atom, the whole thing is neutral (green) because the
positive and negative parts balance out. When the electron leaves, the remaining atom is positive (red). The hole is
wherever you see a red atom, which is missing its outermost electron. (All the other electrons are in that middle
circle with the protons, but we aren't interested in them right now.) As the electrons move one way, from negative to
positive, the holes move the other way, from positive to negative.
You can think about current as the flow of electrons, which go from negative to positive, or as the flow of holes,
which go the other way. If you are working with semi-conductor theory it makes a difference which one you use, but
otherwise you aren't likely to care. We usually use hole flow because the direction agrees with the decision that the
early scientists, like Ben Franklin made when they had to pick a direction to use in their calculations. It's traditional.
Conventional Current Flow vs. Electron Flow

13. Remember; LIKE charges REPEL each other while OPPOSITE charges ATTRACT each other.
Conventional Current Flow vs. Electron Flow

14. TUBE THEORY
Anode (Plate)
Cathode
A diode style tube consists of a positively charged plate, the anode and the negatively charged
cathode. These components are mounted inside a vacuum vessel, or tube.

15. -
Anode (Plate)
Cathode
Heater
Mounted below the cathode is a heater, usually a hot tungsten wire filament.
TUBE THEORY

16. Anode (Plate)
Cathode
Heater
When the heater is turned on, the tungsten filament heats and transfers the heat to the cathode.
TUBE THEORY

17. Heater
Anode (Plate)
Cathode
As the cathode heats it begins to generate free electrons by a process called thermionic emission.
TUBE THEORY

18. Heater
Anode (Plate)
Cathode
As the anode begins to be positively charged, the negatively charged electrons are attracted to it.
TUBE THEORY

19. Anode (Plate)
Cathode (Filament)
The RF tube used in the Rofin laser is a triode style unit where the heater and cathode are combined.
This component is referred to as the filament.
TUBE THEORY

20. Anode (Plate)
Cathode (Filament)
225 ADC
T3 Xfmr
The filament requires constant and considerable power to provide electron flow to the anode. The
filament transformer is supplied 400 VAC (3PH) and is rectified to supply dc current to the filament
precisely set to 225 amps on the DC035-UTA laser (178 AMPS on the DC035).
TUBE THEORY

21. Anode (Plate)
Cathode (Filament)
225 ADC
T3 Xfmr
Grid
There is an additional component used in the triode to control the flow of electrons from the cathode
to the anode; the grid.
TUBE THEORY

22. Anode (Plate)
Cathode (Filament)
225 ADC
T3 Xfmr
-200 V Grid
Current
As we know, the negatively charged electrons from the cathode are attracted to the positively
charged anode. If the grid is held at a negative potential then there will be no attractive forces and,
subsequently, no electron flow to the anode.
TUBE THEORY

23. Anode (Plate)
Cathode (Filament)
225 ADC
T3 Xfmr
0V Grid
Current
If the grid is held at a less negative value then the negatively charged electrons from the cathode will
be attracted to the positively charged anode and begin flowing again.
TUBE THEORY

24. -200V
0V
Anode (Plate)
Cathode (Filament)
225 ADC
T3 Xfmr
If the grid is held at a less negative value then the negatively charged electrons from the cathode will
be attracted to the positively charged anode and begin flowing again.
TUBE THEORY

25. -200V
0V
RLC TUNING
CIRCUIT
80KHz PWM
Grid Signal
80KHz RF Tube Oscillation
80MHz RF Energy
The tube is being oscillated by being turned on and off by the PWM grid signal. The energy is further
conditioned by the RLC tuning circuit. Oscillation is increased to 80MHz with up to 50mw of energy.
TUBE THEORY

26. -200V
0V
RLC TUNING
CIRCUIT
80KHz PWM
Grid Signal
80KHz RF Tube Oscillation
80MHz RF Energy
So to clarify: the tube is simply acting as a switch; required for controlling high power.
TUBE THEORY

27. LC COMPONENTS
CAPACITORS ALLOW AC TO PASS
CAPACITORS BLOCK DC (BLOCKING CAPACITOR)
INDUCTORS BLOCK AC (CHOKE)
INDUCTORS ALLOW DC TO PASS
LC circuits behave as electronic resonators and are used in the following schematics as filters and
tuning circuits.