Scanning temporal ultrafast delay methods and apparatuses therefor

• US 5,778,016 A
• Filed: 02/16/1996
• Issued: 07/07/1998
• Est. Priority Date: 04/01/1994
• Status: Expired due to Term

• Current Assignee: IMRA America Incorporated (Aisin Corp.)
• Original Assignee: IMRA America Incorporated (Aisin Corp.)
• Inventors: Harter, Donald J., Fermann, Martin E., Sucha, Gregg D.
• Primary Examiner(s): Bovernick, Rodney B.
• Assistant Examiner(s): Wise, Robert E.
• Application Number:
  US08/602,457
• Time in Patent Office: 872 Days
• Field of Search: 372/25, 372/38
• US Class Current: 372/38.1
• CPC Class Codes: G01P 3/806 in devices of the type to be classified in G01P3/68
• CPC Class Codes: G01R 13/347 using electro-optic elements
• CPC Class Codes: G01S 17/18 wherein range gates are used
• CPC Class Codes: G01S 17/50 Systems of measurement based on relative movement of target
• CPC Class Codes: G01S 7/484 Transmitters
• CPC Class Codes: G01S 7/486 Receivers
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating
• CPC Class Codes: H01S 3/1398 by using a supplementary modulation of the output
• CPC Class Codes: H01S 3/2383 Parallel arrangements

Abstract

The present invention is directed to methods and apparatuses for performing temporal scanning using ultra-short pulsewidth lasers in which only minimal (micro-scale) mechanical movement is required. The invention also relates to methods for obtaining high-accuracy timing calibration, on the order of femtoseconds. A dual laser system is disclosed in which the cavity of one or more of the lasers is dithered, by using a piezoelectric element. A Fabry-Perot etalon is used to generate a sequence of timing pulses used in conjunction with a laser beam produced by the laser having the dithered laser cavity. A correlator correlates a laser pulse from one of the lasers with the sequence of timing pulses to produce a calibrated time scale. The methods and apparatuses of the present invention are applicable to many applications requiring rapid scanning and time calibration, including, but not limited to metrology, characterization of charge dynamics in semiconductors, electro-optic testing of ultrafast electronic and optoelectronic devices, optical time domain reflectometry, and electro-optic sampling oscilloscopes.

Claims

1. A method for rapidly scanning a first pulse output from a first short-pulse laser and a second pulse output from a second short-pulse laser, comprising the steps of:

detecting a difference between the first and second pulses;

generating a time delay control signal based on said difference detected in said detecting step;

altering a time delay of the second pulse by changing the frequency of pulses output from the second short-pulse laser based on said time delay control signal, thereby stabilizing the second pulse with respect to the first pulse; and

scanning the first pulse and the second pulse altered in said altering step, by changing the time delay of one of the first and second pulses in a predetermined manner.

2. The method for scanning as claimed in claim 1, wherein in said step of altering a time delay by changing the frequency of pulses output from the second short-pulse laser is performed by changing the length of a laser cavity of the second short-pulse laser, and in said scanning step the time delay of one of the first and second pulses is changed by changing the length of the laser cavity of one of the first and second short-pulse lasers, respectively.

3. The method for scanning as claimed in claim 2, wherein the length of a laser cavity of said one of the first and second short-pulse lasers is changed in said scanning step in said predetermined manner by applying one of a square wave, a rectangular wave and a sinusoidal wave to a piezoelectric unit disposed within the laser cavity of said one of the first and second short-pulse lasers.