Information handling apparatus for storing and reading back a continuously variable frequency modulated signal as a non-image, spatially variable and discrete physical pattern upon a record carrier, comprising:
- signal source means for providing a frequency modulated information signal to be recorded, said signal having its information content in the form of a carrier signal having frequency changes in time representing said information to be recorded;
- a record carrier including a substrate having a laser radiation responsive surface for retaining a physical change representative of said information signal;
- said laser radiation responsive surface having a threshold power level above which one such physical change is formed;
- means for imparting uniform motion to said record carrier;
- a first laser source for providing a laser writing beam;
- first optical means for defining a first optical path between said laser source and said laser radiation responsive coating, said first optical means being further employed for focusing said writing laser beam to a spot upon said surface;
- said frequency modulated signal having an amplitude varying between a first higher voltage level and a second lower voltage level;
- laser intensity modulating means positioned in said first optical path between said laser source and said record carrier, said laser intensity modulating means operating over a range between a higher laser transmitting state and a lower laser transmitting state for intensity modulating said writing laser beam with said frequency modulated information signal to be recorded;
- said intensity of said writing laser beam being adjustable relative to said threshold power level of said laser radiation responsive surface;
- said laser beam issuing from said laser intensity modulating means having a prescribed reference intensity level which is intermediate said higher laser transmitting state and said lower laser transmitting state, said prescribed intensity level being equal to said threshold power level of said laser radiation responsive surface;
- said writing laser beam issuing from said laser intensity modulating means during the period corresponding to the period said writing laser beam exceeds said prescribed intensity level being of sufficient intensity for interacting with said radiation responsive surface while said surface is in motion, said writing laser beam corresponding to said period during which said writing laser beam exceeds said prescribed intensity level being of sufficient intensity for imparting a permanent and substantially uniform physical change during said period representative of said information signal;
- said writing laser beam issuing from said laser intensity modulating means during the period corresponding to the time said writing beam is less than said prescribed intensity level having an intensity less than the intensity required for altering said radiation responsive surface;
- said laser intensity modulating means being responsive to said frequency modulated signal and changing between its higher light transmitting state and its lower light transmitting state during each cycle of said frequency modulated signal for intensity modulating said writing laser beam with the frequency modulated electrical signal to be recorded by continuously adjusting the intensity of said writing laser beam under the control of said frequency modulated electrical signal for continuously varying the time said writing beam exceeds its prescribed reference intensity level and is less than its prescribed reference intensity level to track the instantaneous frequency of said frequency modulated signal;
- said higher laser transmitting state corresponding to said first voltage level of said frequency modulated signal, and said lower laser transmitting state corresponding with said second voltage level of said frequency modulated signal;
- said writing laser beam passing through said laser intensity modulating means and focusing upon said radiation responsive surface by said first optical means having sufficient intensity to form a first permanent and substantially uniform physical change in said surface for a first portion of each cycle of said frequency modulated signal during the time that said frequency modulated signal is at said first voltage level, said change being continuously variable in its length to represent the duration of said first portion of the cycle;
- said writing laser beam passing through said laser intensity modulating means and focused upon said radiation responsive surface by said first optical means falling below said intensity required to form a physical change in said surface for the remaining portion of each cycle of said frequency modulated signal during the time that said frequency modulated signal is at said second voltage level, the length of the spacing between adjacent physical changes being continuously variable to represent the duration of said remaining portion of the cycle for recording upon said record carrier a discrete physical pattern representing a non-image spatially variable form of the information to be recorded from which said information signal can be recovered;
- a second laser source for providing a second laser reading beam;
- a second optical means for defining an optical path between said second laser source and said record carrier including a portion of said first optical path, said second optical means being further employed for focusing said second laser beam down to a spot upon said radiation sensitive surface;
- said second laser reading beam being of sufficient intensity for illuminating selected portions of said surface of said carrier arranged as a non-image, spatially variable and discrete physical pattern, said second laser reading beam being specularly reflected from unaltered illuminated portions, and said second laser reading light beam being non-specularly reflected from the other of said illuminated portions;
- said second optical means being further employed for collecting said reflections from said illuminated portions;
- and
- light sensing means responsive to said reflections for generating a frequency modulated electrical signal corresponding to said reflections, said last mentioned frequency modulated signal having its information content in the form of a carrier frequency having frequency changes in time responding to the stored information whereby the informational content of the non-image, spatially variable and discrete physical pattern formed upon said record carrier is retrieved as a continuously variable frequency modulated signal.