Optical scanning and imaging systems based on dual pulsed laser systems

• US 9,252,560 B2
• Filed: 04/08/2014
• Issued: 02/02/2016
• Est. Priority Date: 03/06/2009
• Status: Expired due to Fees

• Current Assignee: IMRA America Incorporated (Aisin Corp.)
• Original Assignee: IMRA America Incorporated (Aisin Corp.)
• Inventors: Fermann, Martin E., Hartl, Ingmar
• Primary Examiner(s): Rodriguez, Armando
• Application Number:
  US14/247,828
• Publication Number:
  US 20140219298A1
• Time in Patent Office: 665 Days
• US Class Current: 1/1
• CPC Class Codes: G01B 9/02001 characterised by controlling or generating intrinsic radiation properties
• CPC Class Codes: G01N 2021/317 Special constructive features
• CPC Class Codes: G01N 21/31 Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry G01N21/72 takes precedence
• CPC Class Codes: G02B 6/02304 Core having lower refractive index than cladding, e.g. air filled, hollow core
• CPC Class Codes: H01S 3/0675 Resonators including a grating structure, e.g. distributed Bragg reflectors [DBR] or distributed feedback [DFB] fibre lasers
• CPC Class Codes: H01S 3/06754 Fibre amplifiers H01S3/06708 takes precedence
• CPC Class Codes: H01S 3/08054 Passive cavity elements acting on the polarization, e.g. a polarizer for branching or walk-off compensation quarter-wave plates in a Q-switch laser H01S3/1124, H01S3/115
• CPC Class Codes: H01S 3/10046 Pulse repetition rate control H01S3/11 takes precedence
• CPC Class Codes: H01S 3/1067 using pressure or deformation
• CPC Class Codes: H01S 3/1068 using an acousto-optical device
• CPC Class Codes: H01S 3/1115 using intracavity saturable absorbers
• CPC Class Codes: H01S 3/13 Stabilisation of laser output parameters, e.g. frequency or amplitude
• CPC Class Codes: H01S 3/1307 Stabilisation of the phase
• CPC Class Codes: H01S 3/1392 by using a passive reference, e.g. absorption cell H01S3/1396, H01S3/1398 take precedence
• CPC Class Codes: H01S 3/1394 by using an active reference, e.g. second laser, klystron or other standard frequency source
• CPC Class Codes: H01S 3/2383 Parallel arrangements

Abstract

The invention relates to scanning pulsed laser systems for optical imaging. Coherent dual scanning laser systems (CDSL) are disclosed and some applications thereof. Various alternatives for implementation are illustrated, including highly integrated configurations. In at least one embodiment a coherent dual scanning laser system (CDSL) includes two passively modelocked fiber oscillators. The oscillators are configured to operate at slightly different repetition rates, such that a difference δf_r in repetition rates is small compared to the values f_r1 and f_r2 of the repetition rates of the oscillators. The CDSL system also includes a non-linear frequency conversion section optically connected to each oscillator. The section includes a non-linear optical element generating a frequency converted spectral output having a spectral bandwidth and a frequency comb comprising harmonics of the oscillator repetition rates. A CDSL may be arranged in an imaging system for one or more of optical imaging, microscopy, micro-spectroscopy and/or THz imaging.

Claims

1. A laser based system for generating optical pulses with a time varying time delay, said system comprising:

an optical source, said source comprising;

at least one mode locked oscillator, said source generating optical pulses at a time-varying repetition rate, said optical pulses characterized by having a frequency comb spectrum comprising first and second individual frequency combs, wherein each of said individual frequency combs comprise frequency teeth separated in frequency, and wherein said optical pulses propagate in a common propagation path;

a repetition rate controller configured to modulate said repetition rate at a modulation rate; and

an optical reference comprising one or more single frequency lasers, said optical reference configured to monitor or control at least one of a time varying difference in repetition rate δ

or a difference in carrier envelope offset frequency, Δ

f_ceo, between said individual frequency combs, said optical-reference generating an output reference signal and comprising at least one optical element configured for generating a first beat signal between an output reference signal and a frequency tooth of said first comb, and a second beat signal between an optical reference signal and a frequency tooth of said second comb.

2. The laser based system according to claim 1, wherein said source further comprises:

a first beam divider downstream of one mode locked oscillator, said beam divider configured to propagate the output of said one mode locked oscillator along two optical paths having different propagation lengths; and

a beam combiner configured to recombine said pulses propagating along said two optical paths.

3. The laser based system according to claim 1, wherein said system further comprises at least one optical element configured to provide for a measurement of a difference in carrier envelope phase, Δ

f_ceo, between said individual frequency combs.

4. The laser based system according to claim 1, wherein said repetition rate controller modulates a cavity length of a corresponding mode locked oscillator.

5. The laser based system according to claim 1, wherein the system comprises a spectral broadening stage down-stream of said source or said at least one mode locked laser.

6. The laser based system according to claim 1, wherein said system comprises detectors to detect an interferogram between said optical pulses.

7. The laser based system according to claim 1, wherein said system further comprises means for generating sampling points at equidistant optical path length differences between the pulses comprising said pulse pair.

8. The laser based system according to claim 1, wherein said source comprises two passively mode locked fiber lasers.

9. The laser based system according to claim 1, further comprising a fiber amplifier configured to amplify said optical pulses propagating in said common optical path.

10. The laser based system of claim 1, wherein said at least one mode locked laser generates a pulse train comprising pulse pairs with a time varying time delay propagating in said common optical path.