Multi-wavelength, ultrashort pulse generation and delivery, with applications in microscopy

• US 9,825,419 B2
• Filed: 08/23/2016
• Issued: 11/21/2017
• Est. Priority Date: 02/28/2014
• Status: Active Grant

• Current Assignee: IMRA America Incorporated (Aisin Corp.)
• Original Assignee: IMRA America Incorporated (Aisin Corp.)
• Inventors: Hori, Takashi, Fermann, Martin E.
• Primary Examiner(s): BOLDA, ERIC L
• Application Number:
  US15/245,082
• Publication Number:
  US 20160365697A1
• Time in Patent Office: 455 Days
• CPC Class Codes: G02F 1/39 for parametric generation or amplification of light, infrared or ultraviolet waves
• CPC Class Codes: G02F 1/392 Parametric amplification
• CPC Class Codes: H01S 2301/08 Generation of pulses with special temporal shape or frequency spectrum
• CPC Class Codes: H01S 2301/085 solitons
• CPC Class Codes: H01S 3/005 Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping shaping laser beam for working metal or other materials B23K26/06; optical elements, systems or apparatus in general G02B
• 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 3/0085 Modulating the output, i.e. the laser beam is modulated outside the laser cavity
• 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 3/06708 Constructional details of the fibre, e.g. compositions, cross-section, shape or tapering optical fibres as passive waveguides G02B6/02
• CPC Class Codes: H01S 3/06758 Tandem amplifiers
• CPC Class Codes: H01S 3/1106 Mode locking
• CPC Class Codes: H01S 3/1608 erbium
• CPC Class Codes: H01S 3/1611 neodymium
• CPC Class Codes: H01S 3/1616 thulium
• CPC Class Codes: H01S 3/1618 ytterbium
• CPC Class Codes: H01S 3/302 in an optical fibre

Abstract

In one aspect, the present disclosure describes a fiber laser system for the generation and delivery of femtosecond (fs) pulses in multiple wavelength ranges. For improved versatility in multi-photon microscopy, an example of a dual wavelength fiber system based on Nd fiber source providing gain at 920 and 1060 nm is described. An example of a three-wavelength system is included providing outputs at 780 nm, 940 nm, and 1050 nm. The systems include dispersion compensation so that high quality fs pulses are provided for applications in microscopy, for example in multiphoton microscope (MPM) systems.

Claims

1. A laser system configured to provide ultrashort pulses at a plurality of output wavelengths, λ

₁ . . . λ

_n, wherein n≧

2, said laser system comprising;

at least one mode locked laser configured to generate ultrashort input pulses having one or more wavelengths;

dispersive optical components disposed downstream from said at least one mode locked laser; and

an optical delivery fiber configured such that at each of said wavelengths, λ

₁ . . . λ

_n, net dispersion exhibited by said at least one mode locked laser, said dispersive optical components and said optical delivery fiber substantially compensates a net dispersion of an end use device disposed downstream from said laser system, said end use device configured to irradiate a sample with ultrashort pulses,

wherein said end use device is configured to deliver femtosecond pulses having a selected plurality of said output wavelengths λ

₁ . . . λ

_n, to said sample, each of said femtosecond pulses substantially compensated for the net dispersion of said laser system and said end use device.

2. The laser system according to claim 1, wherein said at least one mode locked laser comprises at least one mode locked fiber oscillator.

3. The laser system according to claim 2, wherein said at least one mode locked fiber oscillator comprises one or more of an Nd fiber oscillator, a Yb fiber oscillator, an Er fiber oscillator, a Tm fiber oscillator, or a Ho fiber oscillator.

4. The laser system according to claim 2, wherein said at least one mode locked fiber oscillator generates input pulses having one or more wavelengths of said plurality of output wavelengths, λ

₁ . . . λ

_n.

5. The laser system according to claim 1, further comprising an optical modulator receiving pulses at said plurality of wavelengths, said modulator configured to controllably select one or more pulses at said plurality of wavelengths and/or to control the output power at said wavelengths.

6. The laser system according to claim 5, wherein said optical modulator comprises an acousto-optic modulator, an electro-optic modulator, or an integrated Mach Zehnder modulator.

7. The laser system according to claim 1, further comprising a controller in communication with said end use device.

8. The laser system according to claim 1, wherein said optical delivery fiber is configured with pre-selected dispersion at multiple wavelengths of said plurality of output wavelengths, λ

₁ . . . λ

_n.

9. The laser system according to claim 1, wherein n=2, and said wavelengths are approximately 920 nm and 1060 nm.

10. The laser system according to claim 1, wherein n=3, and said wavelengths are approximately 920 nm, 1060 nm, and 1300 nm.

11. The laser system according to claim 1, wherein n=3, and said wavelengths are approximately 780 nm, 940 nm and 1050 nm or approximately 780 nm, 950 nm and 1320 nm.

12. The laser system according to claim 1, wherein said system comprises a Raman shifting fiber configured for Raman soliton propagation.

13. The laser system according to claim 12, wherein said Raman shifting fiber shifts an input wavelength to one or more of the plurality of output wavelengths λ

₁ . . . λ

_n.

14. The laser system according to claim 12, wherein said Raman shifting fiber produces an output wavelength of about 2600 nm, and said system comprises a frequency doubler to generate 1300 nm optical pulses.

15. The laser system according to claim 1, wherein said system comprises a frequency converter configured for upconverting a frequency of optical pulses.

16. The laser system according to claim 1, wherein said system comprises a crystal for difference frequency generation (DFG), and an output from said DFG comprises one of more of the wavelengths λ

₁ . . . λ

_n.

17. The laser system according to claim 1, wherein said optical delivery fiber comprises a hollow core photonic crystal fiber (HC-PCF), a hollow core photonic bandgap fiber (HC-PBGF), or a Kagome fiber.

18. The laser system according to claim 1, wherein said optical delivery fiber exhibits slightly anomalous dispersion at one or more output wavelengths, λ

₁ . . . λ

_n.

19. The laser system according to claim 1, wherein said ultrashort pulses irradiating said sample are nearly transform limited, and comprise pulse widths in the range from about 100 fs to about 1 ps with pulse pedestal substantially below 10% of a peak value of the ultrashort pulses.

20. The laser system according to claim 1, wherein said dispersive components disposed downstream from said at least one mode locked laser comprise specialty fiber arranged to pre-chirp an input signal and vary a pulse width of said input signal via normal or anomalous dispersion.

21. The laser system according to claim 1, wherein λ

₁ . . . λ

_n comprises a wavelength at or near 920 nm.

22. The laser system according to claim 1, said wavelength comprising, as λ

₁, the 900 to 950 nm wavelength range and, as λ

₂, the 1030 to 1080 nm wavelength range, wherein said system configured with a single Nd power amplifier simultaneously amplifying optical pulses having respective wavelengths in each of the two wavelength ranges λ

₁ and λ

₂.

23. The laser system according to claim 1, further comprising:

an optical parametric amplifier (OPA) disposed between said at least one mode locked laser and said optical delivery fiber, wherein said OPA generates a plurality of OPA output wavelengths, n>

2, for use in said end use device, and wherein said optical delivery fiber is configured with dispersion at each of said OPA wavelengths such that compressed optical pulses having pulse widths less than about 200 fs are provided from said end use device to irradiate said sample.

24. An end use device utilizing ultrashort pulses to irradiate a sample, the end use device comprising:

the laser system according to claim 1; and

delivery and focusing optics having predetermined net dispersion at each of a plurality of wavelengths, λ

₁ . . . λ

_n, wherein n≧

2,

wherein the net dispersion in each of said laser system and said end use device at each of said wavelengths λ

₁ . . . λ

_n is sufficiently compensated to result in nearly transform limited ultrashort pulses having pulse widths in the range from about 100 fs to about 1 ps.

25. A laser system configured to generate ultrashort pulses to irradiate a sample, comprising:

a mode locked laser configured to generate input pulses;

a highly nonlinear fiber configured to generate a frequency broadened spectrum downstream of said mode locked laser, said broadened spectrum overlapping at least partially with a signal wavelength range Δ

λ

,

dispersive optical components disposed downstream from said mode locked laser;

an optical parametric amplifier (OPA) disposed downstream from said mode locked laser, said OPA configured to amplify optical pulses with a corresponding pulse spectrum within the wavelength range Δ

λ

; and

an optical delivery fiber configured such that within said wavelength range Δ

λ

, the net dispersion exhibited by said mode locked laser, said dispersive optical components, said OPA, and said optical delivery fiber substantially compensates a net dispersion of an end use apparatus disposed downstream from said laser system, said end use apparatus configured to irradiate a sample with femtosecond pulses generated with said OPA.