RealTime Control and Assessment of Ultrafast LASER Pulses

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Laser Projection System
Design and Construction
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Why LPS?

• Theoretically superior resolution due to the
  coherence of laser light
• Strong advantages in color range offering better
  image quality (twice as many as CRT)

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Initial Design Specifications

• Projection Distance 8-12 ft
• Projection Field Size 3x3 ft
• Image Pixelation gt200x200 pixels
• Refresh Rate gt 4 frames/sec
• Size lt2.5x2.5x0.75
  ft
• Weight lt10 lbs
• monochrome

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Design 1Chopper Array
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Chopper Assembly Refresh Rate
Reshesh Rate vs. Number of Choppers
Refresh RatePixel Count Chopper rate / Number
of Choppers 5Hz(640480) (1.536x106
chops/sec) / N Ngt1
Sample solutions
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Problems With Chopper Design

• Extremely high frequency at which the laser would
  have to be modulated by the choppers to obtain a
  reasonable refresh rate
• Difficult to maintain accuracy needed in the
  laser path to produce a steady image
• COST COST COST
• Chopper arrays of this quality start at 1000
  dollars

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Design 2 Duel Rotating Mirror Assembly
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Problems With 2 mirror Design

• Loss of usable light due to rotating mirrors
  decreasing efficiency
• Cost of increasing the Light (additional lasers
  needed to produce the picture)
• Overall durability and alignment of the device
  during transportation

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Design 3 Rotating and Sliding Mirror Assembly
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Disadvantages of Sliding Mirror

• Extreme vibration due to mirror high speed linear
  movement
• Large number of direction changes of the mirror
  in one second
• As with two mirrors, possibility of misalignment
  of optics is high

A design with only 1 moving optic was decided
upon
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Final Design Single Tilting Mirror Assembly
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Chassis Layout

• LCD mounted 45-50 deg from horizontal
• Laser mounted 4 in below LCD
• Mirror mounted 19 inches from center of LCD

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Mirror Geometry and Assembly
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Specs For Mirror Assembly

• Refresh Rate of 20-30 Frames a second
• (1600 1800 Frames a minute)
• Swept area 6X8 inches Square
• Motor Angular Velocity 800 900 RPMs
• Swept Angle 13 degrees

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Motor Equations
torque to angular velocity
general schematic
torque w/out rotation and angular velocity w/
zero torque
Angular velocity with applied torque
Power output
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Motor Operation
Torque vs. angular velocity
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Equations for mirror mount and LCD
Mirrors Mounted Angles
?rest tan-1(2.206/7.5) 9.65deg from
vertical ?max((tan-1(2.2/12))/2)-9.65 9.65-16
.26/8.13 1.22deg from vertical ?min9.65(tan-1
(2.2/5.4))/2 9.65-22.16/2 20.7deg from
vertical
?Rest angle of mirror is its angle in which to
reflect laser to center of LCD ?max angle of
mirror to reflect to bottom of LCD ?Min angle
of mirror to reflect to top of the LCD
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Initial Idea for GUI Software Package

• Design use a GUI interface to control a
  micro-controller
• Goals
• Run system from computer
• Have the features of controlling the LCD display
  controls

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Why GUI was not developed

• Group decided it was too time consuming to write
  a device driver for the system.
• The XS95 board came with proprietary software for
  interfacing with the computer.
• The design project was more efficient without the
  software package.

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Contrast Ratio vsTransmitted Power

• Trade off between power transmission and contrast
• Angle of incidence chosen to be in range 30-45º

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LCD Projection Panel

• Readily available
• Comparatively affordable (lt150.00)
• Accepts VGA input

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The HeNe

• Helium Neon lasers are of little advantage
• Smaller divergence angle
• Could produce sufficient power with one laser
  (gt100 mW)
• Just too expensive for enough power

Reprinted w permission from Spectra-Physics
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NdYAG Pulsed Laser

• Lots of Power (Watts or tens of Watts)
• Near peak of human brightness sensitivity
• Very expensive (gt1500)

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Laser Diode

• Affordable (12.00 each)
• Very stable, reliable
• Greater beam divergence (could be beneficial)
• One disadvantage being relatively low power

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Diode Laser Operating Characteristics

• Primary wavelength dependence is upon temperature

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Beam Dispersal Mechanism

• Optical system must appropriately disperse beam
  paths across LCD as well as projection field.
• Can be partially accomplished by intrinsic beam
  divergence

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Our beam profile

• Measured divergence angle of 1.4º should be
  adequate
• May need to acquire cheap lenses

Measured at 3 feet
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Laser Diode Housing

• As many as 24 independent AlGaInP lasers
  operating at 635 nm.
• Each at 5 mW output for 120 mW optical power
  total.

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Power Circuit

• Motor 6W
• Fans 2.64 W
• X 95 board low wattage
• LCD screen 18 W
• Laser diodes (0.144 W each)243.46 W

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Standard Motor 18 volt

• Design step down and distribute
• Voltage divided for rotation rate control

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X 95 Board and Fans

• The X 95 has a 4.3ohm resistance and requires
  500mA current from the circuit.
• Seven fans each requiring 12 volts

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Laser Diode

• Potentiometer allows control over current
• Resistor 100 kohms with high tolerance
• Problem with power surges and damage to diodes

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LCD displays power

• Limiter will restrict the current to less than
  1.5 amps
• A fuse will be included to prevent damage
• Problem arose during research

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BUDJECT
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XS95-108 Outline

• Specifications
• Housing of the Board
• Applications of the Board
• Drivers and code using the CPLD
• Downloading code onto the XS Board

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XS95-108 Prototyping Board as Independent Self
Contained System
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Specifications

• 128 K-Byte SRAM
• Sufficient memory for storing pictures
• 9 Volt DC Power Supply
• Acquired at Radio Shack for 15
• Programmable CPLD
• Driving Circuits for PS/2 input and VGA output
• Microcontroller
• PS/2 Parallel Input
• VGA Output
• Clock Oscillator - 25 MHz -gt 60 Hz

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Housing of the XS Board

• Utilized for protection because board is delicate
  and expensive
• Placed on non-conductive surface because of
  grounding pin-outs
• Plastic housing of project box

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Applications of XS Board

• VGA Signal to LCD
• Monitor
• Used as a monitor for a computer
• Pictures
• Stored in SRAM sent by the computer
• Inputted from the PS/2 Port using a mouse or a
  graphics tablet
• PS/2
• Ability to connect a mouse or graphics tablet to
  draw pictures in real-time

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Inputting Pictures Through PS/2Graphics Tablet
vs. Mouse

• Mouse
• Cheap from around 5
• All mice can be powered by PS/2 and converted
  from USB by simple adapter
• More difficult for user to draw picture

• Graphics Tablet
• Cost is very high from 75 - 100
• Newer graphics tablets can not be powered by PS/2
  alone many are only USB
• Ability for the user to input a drawing using a
  pen

RESULTS MOUSE WILL BE IMPLEMENTED
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Driving Circuits Using the CPLD

• VGA Signal
• Two Synchronization Signals
• RGB Output
• Only the red analog output signal will be
  implemented because only a monochrome image is
  necessary
• Pixel Generator
• Converts pictures to a monochrome pixel form

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Horizontal Synchronization Signal

• Used for telling the LCD when to go to the next
  line
• At a resolution of 640 480 the timing of the
  signal is as follows

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Vertical Synchronization Signal

• Used for telling the LCD when to go back to the
  upper left hand corner of the screen
• At a resolution of 640 480 the timing of the
  signal is as follows

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Synchronization Signals in VHDL
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Generating Pixels in C
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Using XILINX to Download Code
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Progress towards Construction

• LCD acquired
• Tested laser diode
• Produced partial image!
• All other parts being acquired
• No actual implementation completed

Approximate Completion
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Work Distribution

• Jeremy Laser housing, optical layout and LCD
• Ryan Mechanical Layout, Motor use and
  cooling/ventilation
• Steve PSX 95 programming and interface
• Charles Stand around and look good