LASER SYSTEM EMPLOYING HARMONIC GENERATION

• US 20090238222A1
• Filed: 05/14/2009
• Published: 09/24/2009
• Est. Priority Date: 01/30/2001
• 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: Harris, Don Ahmasi, Dantus, Marcos, Lozovoy, Vadim V.
• Granted Patent: US 8,208,505 B2
• Time in Patent Office: Days
• US Class Current: 372/22
• CPC Class Codes: G01B 9/02014 by using pulsed light
• CPC Class Codes: G01B 9/02067 by electronic control systems, i.e. using feedback acting on optics or light
• CPC Class Codes: G01B 9/0209 Low-coherence interferometers
• CPC Class Codes: G01B 9/02091 Tomographic interferometers, e.g. based on optical coherence
• 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
• CPC Class Codes: H01S 3/0092 Nonlinear frequency conversion, e.g. second harmonic generation [SHG] or sum- or difference-frequency generation outside the laser cavity nonlinear frequency conversion per se G02F1/35
• CPC Class Codes: H01S 3/10053 Phase control
• CPC Class Codes: H01S 3/2308 Amplifier arrangements, e.g. MOPA

Abstract

A laser system provides harmonic generation in a laser beam pulse. In another aspect of the present invention, a laser operably remits a laser pulse, a gaseous optical medium operably creates third or greater harmonic generation in the pulse, and a controller characterizes and compensates for distortions in the pulse. A further aspect of the present invention employs multiple optical media arranged to cause cascading harmonic generations in a laser pulse.

Claims

1. A laser system comprising a laser operably emitting a laser pulse, a gaseous optical medium operably creating third or greater order harmonic generation in the pulse, and a controller assisting in compensating for spectral phase distortions in the pulse.

2. The system of claim 1 wherein the controller operably uses Multiphoton Intrapulse Interference Phase Scan to measure and compensate for distortions in the pulse.

3. The system of claim 1 wherein the gaseous optical medium is only air.

4. The system of claim 1 further comprising a telescope operably focusing the pulse at least 5 meters away in the gaseous optical medium.

5. The system of claim 1 further comprising a pulse shaper automatically changed by the controller, the pulse being shaped prior to creation of the harmonic generation.

6. The system of claim 1 further comprising a second optical medium changing the harmonic generation of the pulse, the optical media being positioned relative to each other to cascade the harmonic generations in the pulse.

7. The system of claim 1 wherein the gaseous optical medium is an atomic gas.

8. The system of claim 1 wherein the intensity of the third or greater order harmonic generation is used to measure spectral phase distortions and determine the extent of phase distortions in the pulse by the controller.

9. The system of claim 1 wherein the pulse has a duration of less than 5 fs.

10. The system of claim 1 wherein the gaseous optical medium is a plasma.

11. A laser system comprising:

a laser operably emitting a laser beam pulse having a duration of 50 fs or less;

a pulse shaper operably shaping the pulse;

a controller controlling shaping characteristics of the pulse shaper;

a gaseous location creating at least third harmonic generation in the pulse, the gaseous location being remotely located at least 5 meters away from the laser; and

a focusing optic operably focusing the pulse at the gaseous location.

12. The system of claim 11 wherein binary phases are introduced into the pulse by the shaper.

13. The system of claim 11 wherein the focusing optic is a telescope.

14. The system of claim 11 wherein the controller operably uses Multiphoton Intrapulse Interference Phase Scan software to measure and compensate for distortions in the pulse.

15. The system of claim 11 wherein there is only air at the gaseous location.

16. The system of claim 11 further comprising a second location includes changing the harmonic generation of the pulse, the gaseous locations being positioned relative to each other to cascade the harmonic generations in the pulse.

17. The system of claim 11 wherein the gaseous location includes an atomic gas.

18. The system of claim 11 wherein the pulse propagates as a self-generating filament.

19. The system of claim 11 wherein the controller operably identifies a characteristic of a specimen which receives the shaped pulse.

20. The system of claim 11 wherein the pulse shaper operably changes the spectral phase of the pulse to maximize the at least third harmonic generation through a series of automated measurement and compensation steps until the minimum deviation limit is achieved.

21. The system of claim 11 wherein the duration of the pulse is shorter than two optical cycles.

22. A laser system comprising:

a laser operably emitting a laser pulse;

a first optical medium spaced from the laser;

at least a second optical medium spaced from the laser and the first optical medium; and

a pulse shaper located between at least part of the laser and at least one of the optical media;

at least one of the optical media causing third or greater harmonic generation of the pulse;

the other of the optical media changing the harmonic generation of the pulse substantially in-line with the other optical medium; and

the pulse cascading through the pulse shaper, the first optical medium and the second optical medium.

23. The system of claim 22 wherein at least one of the optical media is a gas.

24. A method of operating a laser system comprising:

(a) shaping a laser beam pulse of less than 50 fs;

(b) focusing the shaped pulse in a gas without a crystal to generate third or greater harmonic generation, or zero order harmonic generation in the pulse; and

(c) automatically varying the shape of subsequent pulses to minimize distortions therein.

25. The method of claim 24 further comprising cascading the pulse, after the shaping and focusing, through a subsequent gaseous nonlinear optical medium to change the harmonic generation of the pulse.

26. The method of claim 24 further comprising aiming the pulse at a remote object more than 5 meters away from the laser system.

27. The method of claim 24 further comprising automatically characterizing and compensating for undesired characteristics in the pulses.

28. The method of claim 24 further comprising destroying a remotely located object with the pulse.

29. The method of claim 24 further comprising micromachining an object with the pulse.

30. The method of claim 24 further comprising creating third harmonic generation in the pulse with the gas which is air.

31. The method of claim 24 further comprising using the dependence of the spectrum of the third harmonic on a phase parameter to calculate an optimum pulse compression function.

32. The method of claim 24 further comprising emitting the pulse with a duration of less than 5 fs, and directly measuring and compensating for undesired spectral phase distortions in the pulse.

33. The method of claim 24 further comprising performing surgery with the shaped pulse.

34. The system of claim 24 wherein the gas is plasma.

35. A method of operating a laser system comprising:

(a) emitting a laser pulse;

(b) transmitting the pulse through apertures in an otherwise nontransparent mask;

(c) focusing laser beams emitted from the apertures on a nonlinear medium; and

(d) detecting a self-diffracting signal from at least one of the laser beams.

36. The method of claim 35 further comprising detecting the self-diffracting signal with a spectrometer and emitting the pulse with a fs laser.

37. The method of claim 35 further comprising using Multiphoton Intrapulse Interference Phase Scan to compensate for distortions in the pulse.

38. The method of claim 35 further comprising using a gaseous optical medium to create harmonic generation in the pulse.

39. The method of claim 35 wherein the pulse has an infrared wavelength.

40. A method of operating a laser system comprising:

(a) using at least one reference phase on a laser pulse to assist in determining a characteristic of a nonlinear optical process in at least one pulse;

(b) determining when the nonlinear optical process in the pulse is maximized for various frequencies;

(c) calculating distortions in the pulse; and

(d) determining an appropriate correction to compensate for the distortions.

41. The method of claim 40 further comprising introducing the reference phase into the pulse with a pulse shaper.

42. The method of claim 40 further comprising introducing the reference phase into the pulse with a prism.

43. The method of claim 40 further comprising introducing the reference phase into the pulse with a grating.

44. The method of claim 40 further comprising a programmable controller automatically conducting the determining and calculating steps, and a laser and a spectrometer being connected to and controlled by the controller.

45. The method of claim 40 further comprising using a sinusoidal reference phase to determine the characteristics.

46. The method of claim 40 further comprising using a quadratic reference phase and subsequently a cubic reference phase to determine the characteristics.

47. The method of claim 40 further comprising using a single scan to accurately measure phase distortions, and causing the at least one pulse to have a duration of 5 fs or less.

48. The method according to claim 40, further comprising directly measuring a second derivative of an unknown phase in terms of the reference phase.

49. The method according to claim 40, further comprising using double integration of a phase to compensate for phase distortion in the pulse.

50. The method according to claim 40, further comprising running a Multiphoton Intrapulse Interference Phase Scan by recording an intensity of the nonlinear optical process without a full spectrum.

51. The method according to claim 40, further comprising using the laser pulse for dentistry.

52. The method according to claim 40, further comprising using a gaseous optical medium to create third or greater order harmonic generation in the pulse.

53. A computer program, stored in memory, the program comprising:

(a) a first set of instructions operably causing at least one reference phase on a laser pulse to assist in determining a characteristic of a nonlinear optical process in the pulse;

(b) a second set of instructions operably evaluating nonlinear optical data obtained as a function of a set of reference phases to determine a signal function that describes the maximum nonlinear optical signal as a function of frequency; and

(c) a third set of instructions operably calculating spectral phase of the pulses from the signal function.

54. The computer program of claim 53 further comprising a fourth set of instructions operably determining an appropriate correction to compensate for the distortions.

55. The computer program of claim 53 further comprising a forth set of instructions using a single scan to accurately measure phase distortions in the pulse, and causing the at least one pulse to have a duration of 5 fs or less.

56. The computer program of claim 53, further comprising a set of instructions operably directly measuring a second derivative of an unknown phase in terms of the reference phase.

57. The computer program of claim 53, further comprising a set of instructions using double integration of a phase to compensate for phase distortion in the pulses.

58. The computer program of claim 53, further comprising a set of instructions running a Multiphoton Intrapulse Interference Phase Scan by recording an intensity of the nonlinear optical process without a full spectrum.