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

• US 8,179,932 B2
• Filed: 04/25/2011
• Issued: 05/15/2012
• Est. Priority Date: 01/29/2008
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Ouchi, Toshihiko, Katagiri, Takashi, Furusawa, Kentaro
• Primary Examiner(s): Stultz, Jessica
• Assistant Examiner(s): CARTER, MICHAEL W
• Application Number:
  US13/093,804
• Publication Number:
  US 20110210252A1
• Time in Patent Office: 386 Days
• Field of Search: 372/6, 372/21, 372/22, 372/25, 359/341.1, 359/337.2, 359/337.5
• 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 fiber amplifier configured to amplify and chirp a light pulse from a laser; and

a pulse compressor configured to compress a pulse width of the light 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 wavelength spectrum of the light pulse from the laser,

wherein the rare-earth doped fiber chirps the light pulse so that the light pulse has energy portions in a wavelength region longer than a zero-dispersion wavelength of the rare-earth doped fiber, and

wherein the fiber amplifier is configured to give a loss to the energy portions.

2. The pulse laser apparatus according to claim 1, wherein the fiber amplifier includes a wavelength filter configured to give the loss to the energy portions.

3. The pulse laser apparatus according to claim 1, wherein the rare-earth doped fiber has, at least in a part thereof, a bent portion so that the rare-earth doped fiber gives the loss to the energy portions.

4. The pulse laser apparatus according to claim 1, wherein the rare-earth doped fiber has, at least in a part thereof, a W-shaped sectional refractive-index profile so that the rare-earth doped fiber gives the loss to the energy portions.

5. The pulse laser apparatus according to claim 1, wherein the fiber amplifier suppresses a higher-order nonlinear effect generated during propagation of the light pulse through the rare-earth doped fiber by giving the loss to the energy portions.

6. The pulse laser apparatus according to claim 1, wherein a light pulse 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 is a phenomenon of four-wave mixing.

8. The pulse laser apparatus according to claim 5, wherein the higher-order nonlinear effect 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 a laser beam from the pulse laser apparatus to the photoconductive device or the nonlinear crystal.

11. A terahertz measuring apparatus including:

the 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.