Method for generating femtosecond vortex beams with high spatial intensity contrast

Patent metadata

Field	Value
Publication number	US-9991667-B2
Application number	US-201715481390-A
Country	US
Kind code	B2
Filing date	Apr 6, 2017
Priority date	Apr 21, 2016
Publication date	Jun 5, 2018
Grant date	Jun 5, 2018

Abstract

A method for generating femtosecond vortex beams with high spatial intensity contrast, where a noncollinearly pumped HG beam femtosecond laser generates femtosecond HG beam and a cylindrical lens mode converter converts the femtosecond HG beam to femtosecond LG vortex beam. The HG beam femtosecond laser comprises a pump source, a gain medium, a saturable absorption mirror as mode-locker, and an output coupler with a noncollinear angle between the laser beam and the pump beam in the gain medium, which enables the laser to generate pure, order-tunable femtosecond HG beams. Femtosecond vortex beams obtained after the cylindrical lens converter have high-intensity-contrast, and are topological charge-tunable.

First claim

We claim:

1. A method for generating femtosecond vortex beams with high spatial intensity contrast, comprising:
building a noncollinearly-pumped laser, said noncollinearly pumped laser comprising a pump source for emitting a pump beam, a gain medium, three concave mirrors, a saturable absorption mirror (SAM), and an output coupler,
aligning the laser cavity to generate a laser beam from the output coupler, monitoring pattern of the output laser beam with a CCD camera, rotating the output coupler to form a noncollinear angle θ between the laser beam and the pump beam in the gain medium so that the high-order Hermite-Gaussian beam is generated from the output coupler; the noncollinear angle θ determines an order of HG 0n beam having a lowest threshold pump power and being selected to oscillate, and n is 0 or an integer,
optimizing position of the SAM to obtain stable mode-locking, and generating a high-order femtosecond Hermite-Gaussian beam from the output coupler,
building a cylindrical lens mode converter to convert the high-order femtosecond Hermite-Gaussian beam into a femtosecond Laguerre-Gaussian vortex beam, and
aligning the cylindrical lens mode converter until a pattern of femtosecond LG 0n beam is obtained on the CCD screen;
wherein relationship of the threshold pump power for HG 0,n beam oscillation and the noncollinear angle θ between the laser beam and the pump beam in the gain medium satisfies that, for the noncollinear angle θ, the order of HG 0,n beam with the lowest threshold pump power (P th (HG 0n )) is selected to oscillate in the noncollinearly-pumped laser as follows:

2.
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exp

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Assignees

• Univ Shanghai Jiaotong

Inventors

• Xie Guoqiang
• Qian Liejia
• Qiao Zhen
• Kong Lingchen
• Qin Zhipeng
• Yuan Peng

Classifications

• H01S3/0815

  having 3 reflectors, e.g. V-shaped resonators · CPC title

• H01S3/0014

  Monitoring arrangements not otherwise provided for (photometry G01J1/00, e.g. G01J1/4257; radiation pyrometry G01J5/00; measuring coherence of light G01J9/00; measuring wavelength of light G01J9/00, e.g. G01J9/0246; measuring optical pulses G01J11/00; calorimetrically measuring power of laser beams G01K17/003) · CPC title

• H01S3/1616 Primary

  thulium · CPC title

• H01S3/08059

  Constructional details of the reflector, e.g. shape (mirrors in general G02B5/08; mountings for mirrors G02B7/18) · CPC title

• H01S3/163

  characterised by a crystal matrix · CPC title