# US 12,184,028 B2 · Apparatus and method for generating 780 nm ultrashort-pulsed laser radiation > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,184,028 B2 - Document ID: US12184028B2 - Status: Granted - Kind: B2 - Application number: 17/473,769 - Filed: 2021-09-13 - Published: 2022-03-17 - Granted: 2024-12-31 - Earliest claimed: 2020-09-14 - Assignees: Coherent Scotland Limited - Applicants: Coherent Scotland Limited - Inventors: Lee Cairns - Web page: https://patentgrep.com/patent/US12184028B2 ## CPC - H01S 3/0057: {Temporal shaping, e.g. pulse compression, frequency chirping (soliton generation and propagation G02F1/3513, H01S3/063 and H01S3/108)} - 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)} - H01S 3/06716: {Fibre compositions (per se C03C13/04)or doping with active elements (lasing materials in general H01S3/14)} - H01S 3/094003: {the pumped medium being a fibre} - H01S 3/094042: {of a fibre laser} - H01S 3/1608: {erbium} - H01S 3/1618: {ytterbium} - H01S 3/2308: {Amplifier arrangements, e.g. MOPA} - H01S 3/0675: {Resonators including a grating structure, e.g. distributed Bragg reflectors [DBR] or distributed feedback [DFB] fibre lasers} - H01S 3/06754: {Fibre amplifiers (H01S3/06708 takes precedence)} - H01S 3/1001: {by controlling the optical pumping} - H01S 2301/08: Generation of pulses with special temporal shape or frequency spectrum - H01S 2302/00: Amplification / lasing wavelength - H01S 2303/00: Pumping wavelength - H01S: DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL ## Abstract An erbium fiber laser produces a beam of ultrashort laser pulses having a center wavelength greater than 780 nanometers, an average power greater than 0.5 watt, and a pulse duration less than 200 femtoseconds. The fiber laser includes an erbium fiber amplifier that is energized by a pump beam having a pump wavelength longer than 1520 nanometers. The pump wavelength is selected to provide uniform gain over the broad spectral bandwidth of a seed beam and minimal gain at shorter wavelengths in the fiber amplifier, thereby overcoming gain narrowing and gain shifting. The pump beam has sufficient power to achieve pump saturation in the fiber amplifier. ## Claims ### Claim 1 An ultrashort-pulsed laser, comprising: a seed laser for generating a pulsed signal beam; an optical resonator for generating a pump beam having a pump wavelength greater than or equal to 1520 nanometers; a power amplifier doped with erbium ions, the power amplifier arranged to receive the signal beam from the seed laser and the pump beam from the optical resonator, the erbium ions in a gain volume of the power amplifier energized by the pump beam, the pump beam causing pump saturation and producing a population inversion within the gain volume less than or equal to 57%, the power amplifier generating an amplified signal beam; a pulse compressor for temporally compressing pulses in the amplified signal beam; and a harmonic generator arranged to receive the amplified and compressed signal beam, the harmonic generator generating a second-harmonic beam having a center wavelength greater than or equal to 780 nanometers and a pulse duration less than or equal to 200 femtoseconds. ### Claim 2 (depends on 1) The ultrashort-pulsed laser of claim 1, wherein the pump wavelength is in a range between 1525 nanometers and 1537 nanometers. ### Claim 3 (depends on 2) The ultrashort-pulsed laser of claim 2, wherein the pump wavelength is in a range between 1530 nanometers and 1535 nanometers. ### Claim 4 (depends on 1) The ultrashort-pulsed laser of claim 1, wherein the power amplifier is a gain fiber and the gain volume is a core of the gain fiber. ### Claim 5 (depends on 1) The ultrashort-pulsed laser of claim 1, wherein the power amplifier is a bulk optic made of a crystal or glass doped with erbium ions. ### Claim 6 (depends on 1) The ultrashort-pulsed laser of claim 1, wherein the second-harmonic beam has a pulse duration less than 150 femtoseconds. ### Claim 7 (depends on 1) The ultrashort-pulsed laser of claim 1, wherein the second-harmonic beam has an average power greater than or equal to 0.5 watt. ### Claim 8 (depends on 7) The ultrashort-pulsed laser of claim 7, wherein the second-harmonic beam has an average power greater than 1 watt. ### Claim 9 (depends on 1) The ultrashort-pulsed laser of claim 1, wherein the signal beam generated by the seed laser has a center wavelength greater than or equal to 1560 nanometers. ### Claim 10 (depends on 1) The ultrashort-pulsed laser of claim 1, wherein the signal beam generated by the seed laser has a spectral bandwidth greater than 30 nanometers. ### Claim 11 (depends on 1) The ultrashort-pulsed laser of claim 1, wherein the amplified signal beam generated by the power amplifier has a center wavelength greater than or equal to 1560 nanometers. ### Claim 12 (depends on 1) The ultrashort-pulsed laser of claim 1, wherein the amplified signal beam generated by the power amplifier has a spectral bandwidth greater than 30 nanometers. ### Claim 13 A method for generating an ultrashort-pulsed output laser beam, comprising the steps of: generating a pulsed signal beam; generating a pump beam in an optical resonator, the pump beam having a pump wavelength greater than or equal to 1520 nanometers; delivering the signal beam and the pump beam to a power amplifier doped with erbium ions, the pump beam energizing the erbium ions in a gain volume of the power amplifier, causing pump saturation and producing a population inversion within the gain volume less than or equal to 57%, the power amplifier generating an amplified signal beam; temporally compressing pulses in the amplified signal beam; and converting the amplified and compressed signal beam to the output laser beam by second-harmonic generation, the output laser beam having a center wavelength greater than or equal to 780 nanometers and a pulse duration less than or equal to 200 femtoseconds. ### Claim 14 (depends on 13) The method of claim 13, wherein the pump wavelength is in a range between 1525nanometers and 1537 nanometers. ### Claim 15 (depends on 14) The method of claim 14, wherein the pump wavelength is in a range between 1530nanometers and 1535 nanometers. ### Claim 16 (depends on 13) The method of claim 13, wherein the pump beam produces a population inversion within the gain volume less than or equal to 53%. ### Claim 17 (depends on 13) The method of claim 13, wherein the amplified signal beam generated by the power amplifier has a spectral bandwidth greater than 30 nanometers. ### Claim 18 (depends on 13) The method of claim 13, wherein the output laser beam has a pulse duration less than 150 femtoseconds. ### Claim 19 (depends on 13) The method of claim 13, wherein the output laser beam has an average power greater than or equal to 0.5 watt. ### Claim 20 (depends on 13) The method of claim 13, wherein the output laser beam has an average power greater than 1 watt.