Pulse laser apparatus, terahertz measuring apparatus, and terahertz tomographic apparatus

• US 7,953,130 B2
• Filed: 01/15/2009
• Issued: 05/31/2011
• Est. Priority Date: 01/29/2008
• Status: Expired due to Fees

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Katagiri, Takashi, Ouchi, Toshihiko, Furusawa, Kentaro
• Primary Examiner(s): Harvey; Minsun
• Assistant Examiner(s): Carter; Michael
• Application Number:
  US12/354,716
• Publication Number:
  US 20090213880A1
• Time in Patent Office: 866 Days
• Field of Search: 372/21, 372/22, 372/25, 372/6, 359/337.2, 359/337.5, 359/341.1
• US Class Current: 372/25
• CPC Class Codes: G01N 21/3586 by Terahertz time domain spectroscopy [THz-TDS]
• CPC Class Codes: G01N 21/4795 spatially resolved investigating of object in scattering medium in vivo A61B
• CPC Class Codes: H01S 1/02 solid
• 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 3/06754 Fibre amplifiers H01S3/06708 takes precedence
• CPC Class Codes: H01S 3/2308 Amplifier arrangements, e.g. MOPA

Abstract

A pulse laser apparatus includes a laser configured to generate a pulse of a laser beam, a fiber amplifier, and a pulse compressor. The fiber amplifier includes a rare-earth doped fiber that exhibits normal dispersion at a wavelength of the laser beam generated from the laser. The pulse laser apparatus further includes a unit configured to give a loss to energy portions in a wavelength region corresponding to a zero-dispersion wavelength of the rare-earth doped fiber and/or a wavelength region longer than the zero-dispersion wavelength within a wavelength spectrum of the laser beam having been chirped in the fiber amplifier.

Claims

1. A pulse laser apparatus comprising:

a laser configured to generate a pulse of a laser beam;

a fiber amplifier configured to amplify the pulse from the laser; and

a pulse compressor configured to compress the pulse from the fiber amplifier,

wherein the fiber amplifier includes a rare-earth doped fiber that exhibits normal dispersion at a center wavelength of a spectrum of the pulse from the laser, and

wherein the fiber amplifier includes a unit configured to give a loss to energy portions in a wavelength region corresponding to a zero-dispersion wavelength of the rare-earth doped fiber and a wavelength region longer than the zero-dispersion wavelength within a spectrum of the pulse having been chirped and spread in the fiber amplifier.

2. The pulse laser apparatus according to claim 1, wherein the unit configured to give a loss to the energy portions in the zero-dispersion wavelength region and the wavelength region longer than the zero-dispersion wavelength is a wavelength filter.

3. The pulse laser apparatus according to claim 1, wherein the unit configured to give a loss to the energy portions in the zero-dispersion wavelength region and the wavelength region longer than the zero-dispersion wavelength generates a leakage loss in both the wavelength regions by forming a bent portion at least in a part of the rare-earth doped fiber.

4. The pulse laser apparatus according to claim 1, wherein the unit configured to give a loss to the energy portions in the zero-dispersion wavelength region and the wavelength region longer than the zero-dispersion wavelength is the rare-earth doped fiber having, at least in a part thereof, a W-shaped sectional refractive-index profile.

5. The pulse laser apparatus according to claim 1, wherein the unit configured to give a loss suppresses higher-order nonlinear effects generated during propagation of the laser beam through the rare-earth doped fiber by giving the loss to the energy portions in the zero-dispersion wavelength region and the wavelength region longer than the zero-dispersion wavelength.

6. The pulse laser apparatus according to claim 1, wherein the laser beam generated by the pulse laser apparatus has a pulse width of 20 fs or less and an average output of 200 mW or more.

7. The pulse laser apparatus according to claim 5, wherein the higher-order nonlinear effect to be suppressed is a phenomenon of four-wave mixing.

8. The pulse laser apparatus according to claim 5, wherein the higher-order nonlinear effect to be suppressed is induced Raman scattering.

9. The pulse laser apparatus according to claim 3, wherein a curvature of the bent portion is variable, and the pulse laser apparatus includes a unit configured to adjust the curvature of the bent portion while monitoring a waveform.

10. A terahertz pulse generating apparatus including:

a photoconductive device or a nonlinear crystal; and

the pulse laser apparatus according to claim 1,

wherein a terahertz pulse is generated by irradiating the laser beam from the pulse laser apparatus to the photoconductive device or the nonlinear crystal.

11. A terahertz measuring apparatus including:

the pulse laser apparatus according to claim 1; and

a branch unit arranged to branch an optical output of the pulse laser apparatus into two parts,

wherein one part of the optical output is irradiated to a first photoconductive device or a first nonlinear crystal to generate a terahertz pulse, and the other part of the optical output is irradiated to a second photoconductive device or a second nonlinear crystal such that the second photoconductive device or the second nonlinear crystal operates as a detector, thus performing terahertz time domain spectroscopy in accordance with pump-probe measurement.

12. The terahertz measuring apparatus according to claim 11, wherein light irradiated to the second photoconductive device or the second nonlinear crystal is obtained by passing the laser beam output from the pulse laser apparatus through a higher-harmonic generator and taking light having passed through the higher-harmonic generator as the irradiated light.

13. A terahertz tomographic apparatus wherein internal tomographic image data of a specimen is obtained by measuring a reflected pulse from the specimen with the terahertz measuring apparatus according to claim 11, and an internal tomographic image is output to an output unit on the basis of the obtained data.

14. A terahertz tomographic apparatus wherein resolution in a direction of depth is 5 μ

m or less when internal tomographic image data of a specimen is obtained by measuring a reflected pulse from the specimen with the terahertz measuring apparatus according to claim 11.

15. The pulse laser apparatus according to claim 1, wherein the rare-earth doped fiber is an erbium doped fiber, a thulium doped fiber, or an ytterbium doped fiber.

16. A method of using the pulse laser apparatus according to claim 1, comprising irradiating the laser beam from the pulse laser apparatus to a photoconductive device or a nonlinear crystal to generate a terahertz pulse.

17. A method of using the pulse laser apparatus according to claim 1, comprising:

branching an optical output of the pulse laser apparatus into two parts;

irradiating one part of the optical output to a first photoconductive device or a first nonlinear crystal to generate a terahertz pulse; and

irradiating the other part of the optical output to a second photoconductive device or a second nonlinear crystal such that the second photoconductive device or the second nonlinear crystal detects the terahertz pulse.

18. A pulse laser apparatus comprising:

a laser configured to generate a pulse of a laser beam;

a fiber amplifier configured to amplify the pulse from the laser; and

a pulse compressor configured to compress the pulse from the fiber amplifier,

wherein the fiber amplifier includes a rare-earth doped fiber that exhibits normal dispersion at a center wavelength of a spectrum of the pulse from the laser,

wherein the fiber amplifier includes a unit configured to give a loss to energy portions in a wavelength region corresponding to a zero-dispersion wavelength of the rare-earth doped fiber and/or a wavelength region longer than the zero-dispersion wavelength within a spectrum of the pulse having been chirped and spread in the fiber amplifier,

wherein the unit configured to give a loss to the energy portions in the zero-dispersion wavelength region and/or the wavelength region longer than the zero-dispersion wavelength generates a leakage loss in both the wavelength regions by forming a bent portion at least in a part of the rare-earth doped fiber, and

wherein a curvature of the bent portion is variable, and the pulse laser apparatus includes a unit configured to adjust the curvature of the bent portion while monitoring a waveform.