Course 8. Photonics Applications II

Module 1. Materials Processing- Heat Treating and Welding

    1.1 Interaction of laser light with materials
        1.1.1 Absorption of laser light
            1.1.1.1 Surface properties
            1.1.1.2 Reflectivity
            1.1.1.3 Absorption coefficient
        1.1.2 Heating
            1.1.2.1 Specific heat
            1.1.2.2 Thermal conduction
            1.1.2.3 Thermal diffusivity
        1.1.3 Melting
            1.1.3.1 The heat of fusion
            1.1.3.2 Propagation of the fusion front
            1.1.3.3 Limitations of thermal conductivity
    1.2 Heat treating
        1.2.1 Basics
            1.2.1.1 The austenite-martensite transformation
            1.2.1.2 TTT diagrams
            1.2.1.3 Laser heating
            1.2.1.4 Quenching
            1.2.1.5 Freezing in the hardened phase
        1.2.2 Lasers used- mainly carbon dioxide
        1.2.3 Results
            1.2.3.1 Applicable materials
            1.2.3.2 Absorbing coatings
            1.2.3.3 Hardness achieved
            1.2.3.4 Coverage rates
            1.2.3.5 Case depths
            1.2.3.6 Application (like steering gear assemblies)
    1.3 Welding
        1.3.1 Conduction welding
            1.3.1.1 Description
            1.3.1.2 Lasers used
            1.3.1.3 Applicable materials
            1.3.1.4 Seam rates vs penetration vs power
            1.3.1.5 Limitations due to thermal conduction
            1.3.1.6 Typical application
        1.3.2 Penetration welding
            1.3.2.1 Description of process
            1.3.2.2 Keyholing
            1.3.2.3 Lasers used
            1.3.2.4 Applicable materials
            1.3.2.5 Seam rates vs penetration vs power
            1.3.2.6 Typical application
        1.3.3 Spot welding
            1.3.3.1 Lasers used
            1.3.3.2 Applicable materials
            1.3.3.3 Results
            1.3.3.4 Typical application


Module 2. Materials Processing, Material Removal

    2.1 Basic description
        2.1.1 Phase change
            2.1.1.1 Heat of vaporization
            2.1.1.2 Removal of material by flushing of liquid
        2.1.2 Shielding by blowoff material
            2.1.2.1 Causes
            2.1.2.2 Reduction of material removed
            2.1.2.3 Procedures to reduce the problem
    2.2 Drilling
        2.2.1 Procedures
            2.2.1.1 Fixturing
            2.2.1.2 Motion of workpiece
            2.2.1.3 Lasers used
        2.2.2 Results
            2.2.2.1 Materials-metals and nonmetals
            2.2.2.2 Hole depths
            2.2.2.3 Aspect ratios
            2.2.2.4 Hole shapes
            2.2.2.5 Results for metals
            2.2.2.6 Results for nonmetals
            2.2.2.7 Typical application
    2.3 Cutting
        2.3.1 Basics
            2.3.1.1 Vaporization
            2.3.1.2 Melt removal
            2.3.1.3 Exothermic chemical reaction
        2.3.2 Procedures
            2.3.2.1 Fixturing
            2.3.2.2 Lasers used
            2.3.2.3 Workpiece/beam motion
        2.3.3 Results
            2.3.3.1 Cutting rates vs depth vs power
            2.3.3.2 Results for metals
            2.3.3.3 Results for nonmetals
            2.3.3.4 Edge quality
            2.3.3.5 Polarization effects
            2.3.3.6 Oxygen assist
            2.3.3.7 Nitrogen assist
            2.3.3.8 Typical application
    2.4 Marking
        2.4.1 Dot matrix marking
            2.4.1.1 Process description
            2.4.1.2 Lasers used
            2.4.1.3 Materials
            2.4.1.4 Results
        2.4.2 Image micromachining
            2.4.2.1 Process description
            2.4.2.2 Lasers used
            2.4.2.3 Materials
            2.4.2.4 Results
    `    2.4.3 Engraving
            2.4.3.1 Process description
            2.4.3.2 Lasers used
            2.4.3.3 Materials
            2.4.3.4 Results


Module 3. Materials Processing-Microelectronic Fabrication

    3.1 Applications Involving Material Removal
        3.1.1 Resistor trimming
            3.1.1.1 Process description
            3.1.1.2 Lasers used
            3.1.1.3 Results
            3.1.1.4 Drift
            3.1.1.5 Comparison to competing techniques
            3.1.1.6 Functional trimming
        3.1.2 Via drilling
            3.1.2.1 Lasers used
            3.1.2.2 Vias in polyimide
            3.1.2.3 Vias in circuit boards
        3.1.3 Scribing
            3.1.3.1 Lasers used
            3.1.3.2 Scribing procedures
            3.1.3.3 Comparison to direct cutting
        3.1.4 Marking
            3.1.4.1 Package marking/branding
            3.1.4.2 Wafer serialization
            3.1.4.3 Chip serialization
    3.2 Photolithography
        3.2.1 The photolithographic process
            3.2.1.1 Principles of photolithography
            3.2.1.2 Fabrication of circuit elements by photolithography
            3.2.1.3 Step and repeat process
        3.2.2 The push to higher density
            3.2.2.1 Need for deep UV sources
            3.2.2.2 Currently used light sources
            3.2.2.3 KrF laser photolithography
            3.2.2.4 ArF laser photolithography
        3.2.3 Deep UV laser based systems
            3.2.3.1 KrF laser system capabilities
            3.2.3.2 ArF laser system capabilities
            3.2.3.3 Projections for DRAM density
    3.3 Mask Repair
        3.3.1 Remove excess metallization
            3.3.1.1 Lasers used
            3.3.1.2 Procedures
            3.3.1.3 Results
        3.3.2 Repair of missing metallization
            3.3.2.1 Laser chemical vapor deposition
            3.3.2.2 Lasers used
            3.3.2.3 Procedures
            3.3.2.4 Results
    3.4 Link making and link cutting
        3.4.1. Needs for link making and cutting
            3.4.1.1 Redundancy
            3.4.1.2 Yield enhancement
            3.4.1.3 Personalization
            3.4.1.4 Repair
        3.4.2 Procedures for link cutting and link making
            3.4.2.1 Lasers used
            3.4.2.2 Link cutting by metal vaporization
            3.4.2.3 Link making by metal deposition
            3.4.2.4 Results


Module 4. Materials Processing -
Workstations, Automated Control, Beam Delivery

    4.1 Equipment
        4.1.1 Basic considerations
            4.1.1.1 Laser choice
            4.1.1.2 Beam delivery
            4.1.1.3 Work handling
            4.1.1.4 Motion rates
            4.1.1.5 Accuracy and repeatability
            4.1.1.6 Process monitoring
            4.1.1.7 System configuration
        4.1.2 Typical systems
            4.1.2.1 Gantry systems
            4.1.2.2 Robot systems
            4.1.2.3 Work stations
        4.1.3 Ancillary equipment
            4.1.3.1 Gas handling systems
            4.1.3.2 Gas assist nozzles
            4.1.3.3 Material handling
            4.1.3.4 Damage protection
            4.1.3.5 Beam monitoring - power or pulse energy
            4.1.3.6 Beam quality monitoring equipment
    4.2 Control
        4.2.1 Control systems
            4.2.1.1 Numerical controllers
            4.2.1.2 Computers
            4.2.1.3 Software
            4.2.1.4 Typical complete system
        4.2.2 Control of beam on workpiece
            4.2.2.1 Beam motion
            4.2.2.2 Workpiece motion
            4.2.2.3 Beam and workpiece motion
            4.2.2.4 Flying optic
    4.3 Beam delivery
        4.3.1 Conventional beam delivery
            4.3.1.1 Beam benders
            4.3.1.2 Focusing optics
            4.3.1.3 Atriculated arms
            4.3.1.4 Robotic applications
            4.3.1.5 Protection of optics from spatter
        4.3.2 Fiber optic delivery
            4.3.2.1 Power handling capabilities
            4.3.2.2 Wavelength considerations
            4.3.2.3 Typical system
            4.3.2.4 Beam splitting


Module 5. Applications in Defense

    5.1 Range finding
        5.1.1 Principles
            5.1.1.1 Illuminate target with short pulse of light
            5.1.1.2 Detect reflected return
            5.1.1.3 Measure round-trip time-of-flight
            5.1.1.4 The range equation - gives received power
        5.1.2 Lasers
            5.1.2.1 Nd:YAG
            5.1.2.2 Ruby
            5.1.2.3 Eye-safe
        5.1.3 Typical military range finder system
            5.1.3.1 Optical design
            5.1.3.2 Accuracy
            5.1.3.3 Maximum range
    5.2 Target designators
        5.2.1 Principles
            5.2.1.1 Illuminate target with laser source
            5.2.1.2 Munition homes in on reflected laser light
        5.2.2 Typical military target designator system
            5.2.2.1 Quadrant detectors
            5.2.2.1 Optical design
            5.2.2.3 Accuracy of munition delivery
            5.2.2.3 Maximum range
    5.3 Night vision devices
        5.3.1 Image intensifiers
            5.3.1.1 Contain imaging optics, photocathode and phosphor
            5.3.1.2 Electrons from photocathode accelerated and
                        focused on phosphor
            5.3.1.3 Output of phosphor same as image but brighter
            5.3.1.4 Gain up to 300 possible
        5.3.2 Starlight scopes
            5.3.2.1 Peak in starlight intensity in near infrared
            5.3.2.2 Optical design
            5.3.2.3 Performance
        5.3.3 Infrared imagers
            5.3.3.1 Thermal radiation from heated bodies
            5.3.3.2 Atmospheric transmission of infrared radiation
            5.3.3.3 Forward-looking infrared (FLIR) systems
                - Optical design
                - 3-5 mm systems
                - 8-12 mm systems
                - Performance
                - The common modular FLIR
    5.4 Displays
        5.4.1 Cockpit displays
            5.4.1.1 Requirements: Luminance, resolution, update rate
            5.4.1.2 Types used
                - Cathode ray tubes
                - Light emitting diodes
                - Liquid crystal displays
                - Heads-up displays
        5.4.2 Ship-based displays
            5.4.2.1 Requirements: Luminance, resolution, update rate
            5.4.2.2 Types used
                - Cathode ray tubes dominate
                - Flat panel displays coming into use
        5.4.3 War-room displays
            5.4.3.1 Requirements: Luminance, resolution, update rate
            5.4.3.2 Types used
                - Cathode ray tubes
                - Flat panel displays
                - Light-valve projection displays
    5.5 Directed energy weapons
        5.5.1 Ability to deliver high irradiance at a distance
            5.5.1.1 The diffraction limit
            5.5.1.2 Atmospheric effects
            5.5.1.3 Irradiance at a target vs wavelength
        5.5.2 Lasers considered    
            5.5.2.1 Carbon dioxide
            5.5.2.2 Chemical - The MIRACL laser
            5.5.2.3 Iodine
            5.5.2.4 Excimer
        5.5.3 Pointing and tracking
            5.5.3.1 Difficulties (extreme range, atmospheric turbulence)
            5.5.3.2 Stabilization, pointing and tracking systems
            5.5.3.3 The Airborne Laser Lab
        5.5.4 An unclassified assessment of the capabilities of
                 directed energy weapons


Module 6. Optical Data Storage-CDs, Computer Memory

    6.1 Principles of optical data storage
        6.1.1 Data bits recorded along circular tracks on a rotating disc
            6.1.1.1 May be recorded by a loser beam focused to a diffraction-limited spot
            6.1.1.2 Very high data density possible
        6.1.2 Data bits change reflectivity or polarization of light
            6.1.2.1 Data interpreted as digital ones and zeros
            6.1.2.2 Information retrieved using laser light following the circular tracks
            6.1.2.3 Organization of memory is bit serial
            6.1.2.3 Random access time
    6.2 Types of optical data storage systems
        6.2.1 Read only
            6.2.1.1 Materials used
            6.2.1.2 Recording procedures
            6.2.1.3 Readout procedures
            6.2.1.4 Typical system configuration
            6.2.1.5 Performance specifications
        6.2.2 Write-once, read mostly
            6.2.2.1 Materials used
            6.2.2.2 Recording procedures
            6.2.2.3 Readout procedures
            6.2.2.4 Typical system configuration
            6.2.2.5 Data density available
            6.2.2.6 Data rates
            6.2.2.7 Access times
        6.2.3 Rewritable
            6.2.3.1 The magneto-optical effect
            6.2.3.2 Materials used
            6.2.3.3 Recording procedures
            6.2.3.4 Readout procedures
            6.2.3.5 Typical system configuration
            6.2.3.6 Data density available
            6.2.3.7 Data rates
            6.2.3.8 Access times
        6.2.4 Comparison to competing technologies
            6.2.4.1 Plot of capacity vs access time
            6.2.4.2 Comparison to semiconductor memories
            6.2.4.3 Comparison to magnetic discs and tapes
    6.3 Lasers used
        6.3.1 Current systems
            6.3.1.1 AlGaAs
            6.3.1.2 AlInGaP
        6.3.2 Developing systems
            6.3.2.1 Data density scales as reciprocal of the square of the wavelength
            6.3.2.2 Blue and green laser diodes
    6.4 Applications
        6.4.1 Compact discs
            6.4.1.1 Prerecorded
            6.4.1.2 Mostly audio
            6.4.1.3 Video disc applications developing
        6.4.2 Digital map systems
            6.4.2.1 WORM systems
            6.4.2.2 Used on military aircraft
            6.5.2.3 Shock and vibration requirements
        6.4.3 Computer memory
            6.4.3.1 Rewritable
            6.4.3.2 Personal computer memories
            6.4.3.3 Removable CD systems
            6.4.3.4 "Juke box" systems
    6.5 Holographic memories
        6.5.1 Structure of a holographic memory
            6.5.1.1 Organization of data
            6.5.1.2 Parallel nature of storage
            6.5.1.3 The recording process
            6.5.1.4 Potentially very large storage
            6.5.1.5 The data recovery process
            6.5.1.6 Potential very high speed of data recovery
            6.5.1.7 Typical system configuration
        6.5.2 Status of development
    `        6.5.2.1 Lags behind bit-oriented optical memory
            6.5.3.2 Needs for advances in spatial light modulators
            6.5.3.3 Needs for advances in holographic recording materials


Module 7. Applications in Graphic Arts

    7.1 Introduction to laser graphics
        7.1.1 Lasers used in systems to record and reproduce graphic
                 and textual information
            7.1.1.1 Used for phototypesetting and platemaking
            7.1.1.2 Laser printers to be covered in next module
        7.1.2 Lasers used
            7.1.2.1 Originally helium-neon and air cooled argon
            7.1.2.2 More recently diode and diode=pumped Nd:YAG
        7.1.3 Advantages
            7.1.3.1 Deals with photographs, line art and text all on one
                        piece of equipment
            7.1.3.2 Eliminates several steps in the generation of printing plates
            7.1.3.3 Saves cost and time
            7.1.3.4 Reduces use of wet chemicals
        7.1.4 Materials used
            7.1.4.1 Silver halide photographic film
            7.1.4.2 Dry photographic film (developed by heat)
            7.1.4.3 Photoresist
            7.1.4.4 Photopolymers
            7.1.4.5 Polyesters
    7.2 Systems to generate printing plate directly from paste-up
        7.2.1 Laser beam scans the paste-up
            7.2.1.1 Detector views the reflected light
            7.2.1.2 Generates a signal used for controlling the platemaking
        7.2.2 Second laser scans the plate in synchronism with the laser
                 scanning the paste-up
            7.2.2.1 Laser power modulated by signal from the detector
            7.2.2.2 This procedure generates a printing plate
            7.2.2.3 The plate is then mounted on the press
    7.3 Systems to generate printing plates directly from a computer
        7.3.1 Direct to press systems
            7.3.1.1 Laser scans the plate material
            7.3.1.1 Output from computer modulates the laser power
            7.3.1.3 Plate fabricated right on the printing press
        7.3.2 Example of a specific system
            7.3.2.1 488 nm argon laser scanned in a raster pattern
            7.3.2.2 Laser wrote images directly on polymer-based offset printing plates
            7.3.2.3 Allowed publishing of a color magazine
    7.4 Phototypesetting
        7.4.1 Involves photographing characters on film
            7.4.1.1 Negative of desired character selected via keyboard
            7.4.1.2 Image of character projected onto recording medium
            7.4.1.3 The medium is later used to make the printing surface
        7.4.2 Phototypesetting has been used for newspapers
            7.4.2.1 Laser phototypesetting has reduced costs
            7.4.2.2 Laser phototypesetting has reduced time to prepare plates


Module 8. Consumer Products: Bar Code
Scanners, Laser Printers

    8.1 Bar code scanners
        8.1.1 Bar code scanner is a type of image processor
            8.1.1.1 Nature of the bar code
            8.1.1.2 Code contains information on the item and its price
        8.1.2 Basic operation of the bar code scanner
            8.1.2.1 Laser light scanned over code
            8.1.2.2 Photodetector detects scattered light
            8.1.2.3 Computer processes the signal from the detector
                        and determines what the object is
        8.1.3 Type of laser
            8.1.3.1 Originally helium-neon
            8.1.3.2 Now usually visible diode laser
        8.1.4 Scan optics
            8.1.4.1 Originally a lens and rotating mirror system
            8.1.4.2 Now usually a hologram scanner, which uses
                        a rotating hologram
            8.1.4.3 Hologram scanners smaller and less complex
            8.1.4.4 Hologram scanner produces multiple beams to
                        ensure that at least one is reflected off the bar code
    8.2 Laser printers
        8.2.1 Laser printers use electrophotography
            8.2.1.1 Photoconductive surface charged by ions from a corona discharge
            8.2.1.2 Surface exposed by scanning a laser beam across it
            8.2.1.3 Intensity of beam varied to produce the desired pattern
            8.2.1.4 Photoconductive layer becomes conducting where light intensity was high
            8.2.1.5 Electric charge moves thru the photoconductor and produces a
                        replica of the pattern
            8.2.1.6 Toner particles spread across surface and adhere in the charged areas
            8.2.1.7 Toner particles transferred to paper by application of the corona discharge
            8.2.1.8 The image is fixed on the paper by heat
            8.2.1.9 The surface is cleaned to be ready for the next image
        8.2.2 Lasers used
            8.2.2.1 Originally helium-neon lasers used
            8.2.2.2 Now visible diode lasers used
    8.4 Compact discs
        8.4.1 Read only optical memory device discussed in Module 8-6
            8.4.1.1 Main use is in audio reproduction
            8.4.1.2 This represents the largest number of lasers used
            8.4.1.3 Video optical compact discs are developing
        8.4.2 Typical structure of an audio CD player
            8.4.2.1 Laser is an infrared diode laser
            8.4.2.2 Digital information stored in prerecorded digital
                        pattern of varying reflectivity in tracks on the disc
            8.4.2.3 Detector views pattern of varying reflected light intensity
            8.4.2.4 This digital pattern is then reconverted to music
        8.4.3 Advantages of compact discs
            8.4.3.1 No contact between disc and read head, so noise is low
            8.4.3.2 Imperfections on disc surface are out of focus and have no effect
            8.4.3.3 Large distance (1 mm) between disc and read head,
                        so tolerances are relieved

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