LASER PULSE SYNTHESIS SYSTEM

• US 20100187208A1
• Filed: 01/22/2010
• Published: 07/29/2010
• Est. Priority Date: 01/23/2009
• Status: Active Grant

• Current Assignee: The Board of Trustees of Michigan State University (Michigan State University)
• Original Assignee: The Board of Trustees of Michigan State University (Michigan State University)
• Inventors: Lozovoy, Vadim V., Dantus, Marcos
• Granted Patent: US 8,675,699 B2
• Time in Patent Office: Days
• US Class Current: 219/121.720
• CPC Class Codes: B23K 26/0624 using ultrashort pulses, i.e. pulses of 1ns or less
• CPC Class Codes: B23K 31/125 Weld quality monitoring
• CPC Class Codes: G01J 11/00 Measuring the characteristics of individual optical pulses or of optical pulse trains
• CPC Class Codes: H01S 3/0057 Temporal shaping, e.g. pulse compression, frequency chirping soliton generation and propagation G02F1/3513, H01S3/063 and H01S3/108

Abstract

A laser pulse synthesis system is provided. A further aspect of the present system uses a phase-only modulator to measure ultrashort laser pulses. An additional aspect achieves interferences between split subpulses even though the subpulses have different frequencies. Yet another aspect of a laser system employs multi-comb phase shaping of a laser pulse. In another aspect, a laser system includes pulse characterization and arbitrary or variable waveform generation through spectral phase comb shaping.

Claims

1. A method of using a laser system, the method comprising:

(a) emitting at least one laser pulse;

(b) shaping the pulse with a phase-only modulator;

(c) separating the pulse into at least two replica subpulses by using a phase in the modulator that interacts with at least two frequency subsets of the pulse, each subset representing a pulse; and

(d) measuring a characteristic induced by at least one of the subpulses after step (c).

2. The method of claim 1, further comprising:

(e) supplying a linear pulse function to only some of the pixels of the modulator for at least one of the subpulses; and

(f) supplying a different phase function to other of the pixels of the modulator for at least another of the subpulses, simultaneously with step (e).

3. The method of claim 1, wherein the shaper is a two-dimensional phase mask which supplies different functions to a single pulse.

4. The method of claim 1, wherein the measured characteristic is a duration of the pulse.

5. The method of claim 1, wherein the measured characteristic is autocorrelation.

6. The method of claim 1, wherein the measured characteristic is cross-correlation.

7. The method of claim 1, wherein the modulator is a programmable spatial light modulator, and the subpulses are temporally separated.

8. A method of using a laser system comprising:

(a) separating a laser pulse into at least two subpulses in time but not in space; and

(b) independently shaping each of the subpulses using different chirp functions in a piecewise manner.

9. The method of claim 8, further comprising shaping the pulse with a phase-only modulator.

10. The method of claim 8, further comprising shaping the pulse with a phase- and polarization-only modulator.

11. The method of claim 8, further comprising shaping the subpulses with a phase-only modulator, supplying a first shaping function to some pixels of the modulator for the one of the subpulses, and supplying a second and different shaping function to some pixels of the modulator for at least a second of the subpulses.

12. The method of claim 8, further comprising using software instructions to automatically vary a pulse shaper to shape the subpulses.

13. The method of claim 8, further comprising generating and characterizing optical pulse trains where a spectral phase of every laser pulse in the train is independently controlled.

14. The method of claim 8, further comprising characterizing the laser pulse in which the phase of an input pulse to an amplifier is shaped to enable measuring of the output pulse using a spectrometer located substantially at a target, and without requiring mechanical movement of any optics during operation.

15. The method of claim 8, further comprising using the laser pulse for machining a workpiece.

16. The method of claim 8, further comprising using the laser pulse for biomedical imaging.

25. The method of claim 14, further comprising detecting nonlinear optical excitation in the laser pulse.

17. A method of using a laser system, the method comprising generating and characterizing optical pulse trains where a spectral phase of every laser pulse in the train is independently controlled.

18. The method of claim 17, further comprising using a frequency comb to generate the multi-pulse train.

19. The method of claim 17, further comprising:

(a) splitting a laser spectrum into at least two groups of frequencies distributed over an entire spectrum bandwith;

(b) adjusting the two groups of frequencies such that a desired amplitude and bandwidth for each subpulse is achieved;

(c) imposing the desired phase mask on each of the subsets of frequencies; and

(d) creating a piecewise phase function across the original spectrum to generate a desired pulse sequence.

20. The method of claim 17, further comprising obtaining frequency-resolved autocorrelation of the pulse at the focus by creating at least two pseudo-replicas and recording a second harmonic generation spectrum as a function of their relative time delay.

21. The method of claim 17, further comprising shaping the subpulses with a phase-only modulator, supplying a first shaping function to some pixels of the modulator for the one of the subpulses, and supplying a second and different shaping function to some pixels of the modulator for at least a second of the subpulses.

22. The method of claim 17, further comprising using software instructions to automatically vary a pulse shaper to shape the subpulses.

23. The method of claim 17, further comprising using the laser pulse for machining a workpiece.

24. The method of claim 17, further comprising using the laser pulse for biomedical imaging.

26. A method of using a laser system, the method comprising:

(a) emitting a laser pulse;

(b) shaping the pulse;

(c) splitting the pulse into subpulses being of identical duration to the original pulse except having different frequencies;

(d) causing nonlinear optical interference between the subpulses; and

(e) measuring interferometric correlation between the subpulses.

27. The method of claim 26, wherein the interference is constructive.

28. The method of claim 26, wherein the interference is destructive.

29. The method of claim 26, further comprising temporally delaying one interfering subpulse from another.

30. The method of claim 26, further comprising measuring a carrier frequency of at least one of the subpulses.

31. The method of claim 26, further comprising changing a carrier frequency of at least one of the subpulses.

32. The method of claim 26, further comprising changing the interference with a pulse shaper and without mechanical component movement.

33. The method of claim 26, further comprising encoding communications information into the subpulses with a pulse shaper.

34. The method of claim 26, further comprising using the subpulsses for optical imaging.

35. The method of claim 26, further comprising using the subpulses to micromachine a workpiece.

36. The method of claim 26, further comprising double passing the pulse through a pulse shaper to reduce space-time coupling.

37. The method of claim 26, wherein the correlation is autocorrelation.

38. The method of claim 26, wherein the correlation is cross-correlation.

39. A method of using a laser system, the method comprising:

(a) emitting at least one original laser pulse, each having a duration of less than 1 picosecond;

(b) shaping the original laser pulse with at least two distinct phase functions;

(c) using each phase function to sample available spectral bandwidth of the original pulse;

(d) creating pulse replicas, each having the same pulse duration as the original pulse; and

(e) controlling the replica pulses by distributing each of the phase functions across the spectrum of the associated pulse.

40. The method of claim 39, further comprising controlling relative amplitude between the replica pulses.

41. The method of claim 39, further comprising controlling relative bandwidth between the replica pulses.

42. The method of claim 39, further comprising controlling relative duration between the replica pulses.

43. The method of claim 39, further comprising controlling relative inter-replica time delay between the replica pulses.

44. The method of claim 39, further comprising controlling absolute phase between the replica pulses.

45. The method of claim 39, further comprising using the laser pulse for machining a workpiece.

46. The method of claim 39, further comprising using the laser pulse for biomedical imaging.

47. The method of claim 39, further comprising detecting nonlinear optical excitation in the laser pulse.

48. The method of claim 39, further comprising characterizing the laser pulse in which the phase of an input pulse to an amplifier is shaped to enable measuring of the output pulse using a spectrometer located substantially at a target, and without requiring mechanical movement of any optics during operation.

49. The method of claim 39, further comprising creating an additional reference pulse with the pulse shaper and software instructions, causing the reference pulse to scan across a pulse sequence to provide a cross-correlation of the sequence.

50. A method of using a laser system, the method comprising:

(a) emitting at least one original laser pulse, each having a duration of less than 1 picosecond;

(b) introducing at least two distinct phase functions by pulse shaping;

(c) creating pulse replicas, each having the same pulse duration as the original pulse;

(d) distributing each phase function across the spectrum of the associated pulse;

(e) encoding pulse sequences with information; and

(f) detecting the pulse sequences based on a nonlinear optical process.

51. The method of claim 50, further comprising introducing π

phase shifts in contiguous pixels of a pulse shaper, where the total number of zero and π

pixels is equal, if a given replica pulse needs to be cancelled.

52. The method of claim 50, further comprising introducing π

phase shifts in alternate phase locations, where the total number of zero and π

pixels is equal, if a given replica pulse needs to be cancelled.

53. The method of claim 50, further comprising creating an additional reference pulse with a pulse shaper and software instructions, and causing the reference pulse to scan across a pulse sequence to provide a cross-correlation of the sequence.

54. A laser system comprising:

a phase-only pulse shaper operably splitting a laser pulse into subpulses each being replicas of the original pulse except having different frequencies and temporal delays;

a detector operably detecting a characteristic of the subpulses; and

a programmable controller connected to the pulse shaper and detector, the controller operably sending a shaping signal to the pulse shaper and receiving a signal indicative of subpulse correlation from the detector.

55. The system of claim 54, wherein the detector is a spectrometer which sends a signal to a controller containing software that automatically controls and varies the pulse shaper.

56. The system of claim 54, wherein the software causes the pulse shaper to introduce π

phase shifts in contiguous pixels of the shaper, where the total number of zero and π

pixels is equal, if a given replica pulse needs to be cancelled.

57. The system of claim 54, wherein the software causes the pulse shaper to introduce π

phase shifts in alternate phase locations, where the total number of zero and π

pixels is equal, if a given replica pulse needs to be cancelled.

58. The system of claim 54, wherein a duration of the laser pulse is less than 1 picosecond.

59. A laser system comprising at least two continuous laser sources that are phase locked, and a highly nonlinear optical fiber causing the generation of a comb of frequencies, wherein the phase of all the comb frequencies is measured and corrected to produce a train of ultrashort pulses using multiphoton intrapulse phase scan software instructions.

60. The system of claim 59, wherein a single pulse is selected by nonlinear mixing with a gating pulse taken from the original train of the laser pulses.

61. The system of claim 59, wherein the pulse shaper uses circular polarization in a grating pulse to select a single pulse.

62. The system of claim 59, wherein a train of the laser pulses is used to cause nonlinear optical excitation.

63. The system of claim 59, wherein a laser pulse output is frequency doubled to obtain shorter pulses with improved contrast ratio.

64. The system of claim 59, wherein a laser pulse output is used to seed a pulse amplifier for pulses having a duration less than 1 picosecond.