# US 7,742,509 B2 · Single-longitudinal mode laser with orthogonal-polarization traveling-wave mode > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,742,509 B2 - Document ID: US7742509B2 - Status: Granted - Kind: B2 - Application number: 12/237,735 - Filed: 2008-09-25 - Published: 2010-03-25 - Granted: 2010-06-22 - Earliest claimed: 2008-09-25 - Assignees: Photop Technologies, Inc. - Inventors: Yingjun Ma; Shijie Gu; Li Wu; Hehui Wu; Weimin Chen; Yanli Wang - Web page: https://patentgrep.com/patent/US7742509B2 ## CPC - H01S 3/08031: Single-mode emission - H01S 3/08036: using intracavity dispersive, polarising or birefringent elements - 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)} - H01S 3/09415: {the pumping beam being parallel to the lasing mode of the pumped medium, e.g. end-pumping} - H01S 3/10061: {Polarization control} - H01S 3/1028: {by controlling the temperature} - H01S 3/1611: {neodymium} - H01S 3/1671: {vanadate, niobate, tantalate} - H01S 3/1673: {YVO4 [YVO]} - 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 A single longitudinal-mode laser includes a first mirror and a second mirror that define a laser cavity therein that does not include a linear polarizer. A birefringent gain medium can generate a lasing light at a lasing wavelength along a light propagation direction in response to a pump light at a pumping wavelength. The birefringent gain medium has an optical axis substantially perpendicular to the light propagation direction. A first wave plate positioned between the first mirror and the birefringent gain medium is a quarter wave plate at the lasing wavelength and a whole wave plate at the pumping wavelength. A second wave plate is positioned between the birefringent gain medium and the second mirror. The first wave plat and the second wave plate in part produce a single longitudinal mode in the lasing light. ## Claims ### Claim 1 A single longitudinal-mode laser, comprising: a first mirror; a second mirror, wherein the first mirror and the second mirror define a laser cavity therein, wherein the first mirror is configured to allow a pump light at a pumping wavelength to enter the laser cavity, wherein there is no linear polarizer positioned within the laser cavity; a birefringent gain medium configured to generate a lasing light at a lasing wavelength along a light propagation direction in response to the pump light, wherein the birefringent gain medium has an optical axis substantially perpendicular to the light propagation direction, wherein the second mirror is configured to output at least a portion of the lasing light out of the laser cavity to form an output laser; a first wave plate positioned between the first mirror and the birefringent gain medium, wherein the first wave plate is a quarter wave plate at the lasing wavelength and a whole wave plate at the pumping wavelength; and a second wave plate positioned between the birefringent gain medium and the second mirror, wherein the first wave plat and the second wave plate in part produce a single longitudinal mode in the lasing light. ### Claim 2 (depends on 1) The single longitudinal-mode laser of claim 1, wherein the first wave plate has a first fast axis substantially perpendicular to the light propagation direction, wherein the first fast axis is at a first angle relative to the optical axis of the birefringent gain medium, wherein the first angle is between 30 and 60 degrees. ### Claim 3 (depends on 2) The single longitudinal-mode laser of claim 2, wherein the first wave plate has a first slow axis substantially perpendicular to the first fast axis and the light propagation direction. ### Claim 4 (depends on 2) The single longitudinal-mode laser of claim 2, wherein the second wave plate has a second fast axis substantially perpendicular to the light propagation direction and to the first fast axis. ### Claim 5 (depends on 4) The single longitudinal-mode laser of claim 4, wherein the second wave plate has a second slow axis substantially perpendicular to the second fast axis and the light propagation direction. ### Claim 6 (depends on 1) The single longitudinal-mode laser of claim 1, wherein the birefringent gain medium is configured to generate a first linearly polarized lasing light having a first linear polarization parallel to the optical axis of the birefringent gain medium, wherein the second wave plate is configured to produce a first circularly polarized lasing light, wherein the second mirror is configured to reflect the first circularly polarized lasing light to produce a second circularly polarized lasing light, wherein the second wave plate is configured to produce a second linearly polarized lasing light having a second linear polarization perpendicular to the optical axis of the birefringent gain medium in response to the second circularly polarized lasing light. ### Claim 7 (depends on 1) The single longitudinal-mode laser of claim 1, wherein the birefringent gain medium, the first wave plate and the second wave plate are configured to produce the lasing light in a single longitudinal mode when the pump light has a pump power between a threshold pump power and a maximum pump power that is at least 20 times of the threshold pump power. ### Claim 8 (depends on 7) The single longitudinal-mode laser of claim 7, wherein the threshold pump power is below 50 mW, and wherein the maximum pump power is more than 1000 mW. ### Claim 9 (depends on 7) The single longitudinal-mode laser of claim 7, wherein the output laser has a power more than 500 mW when the pump power is at about 1000 mW. ### Claim 10 (depends on 7) The single longitudinal-mode laser of claim 7, wherein the wavelength of the output laser has a variation smaller than 0.3 nm when the pump power varies from the threshold pump power and the maximum pump power. ### Claim 11 (depends on 7) The single longitudinal-mode laser of claim 7, wherein the slope efficiency of the output laser is more than 60%. ### Claim 12 (depends on 1) The single longitudinal-mode laser of claim 1, wherein the birefringent gain medium, the first wave plate and the second wave plate are configured to produce the lasing light in a single longitudinal mode thereby producing the output laser having a wavelength variation less than 0.3 nm over a temperature range from 10° C. to 40° C. ### Claim 13 A single longitudinal-mode laser, comprising: a first mirror; a second mirror, wherein the first mirror and the second mirror define a laser cavity therein, wherein the first mirror is configured to allow a pump light at a pumping wavelength to enter the laser cavity, wherein there is no linear polarizer positioned within the laser cavity; a birefringent gain medium configured to generate a lasing light at a lasing wavelength along a light propagation direction in response to the pump light, wherein the birefringent gain medium has an optical axis substantially perpendicular to the light propagation direction, wherein the second mirror is configured to output at least a portion of the lasing light out of the laser cavity to form an output laser; a first wave plate positioned between the first mirror and the birefringent gain medium, wherein the first wave plate has a first fast axis substantially perpendicular to the light propagation direction, wherein the first fast axis is at a first angle relative to the optical axis of the birefringent gain medium, wherein the first angle is between 30 and 60 degrees; and a second wave plate positioned between the birefringent gain medium and the second mirror, wherein the second wave plate has a second fast axis substantially perpendicular to the light propagation direction and to the first fast axis, wherein the first wave plat and the second wave plate in part produce a single longitudinal mode in the lasing light. ### Claim 14 (depends on 13) The single longitudinal-mode laser of claim 13, wherein the birefringent gain medium is configured to generate a first linearly polarized lasing light having a first linear polarization parallel to the optical axis of the birefringent gain medium, wherein the second wave plate is configured to produce a first circularly polarized lasing light, wherein the second mirror is configured to reflect the first circularly polarized lasing light to produce a second circularly polarized lasing light, wherein the second wave plate is configured to produce a second linearly polarized lasing light having a second linear polarization perpendicular to the optical axis of the birefringent gain medium in response to the second circularly polarized lasing light. ### Claim 15 (depends on 13) The single longitudinal-mode laser of claim 13, wherein the first wave plate is a quarter wave plate at the lasing wavelength and a whole wave plate at the pumping wavelength, wherein the first wave plate is a quarter wave plate at the lasing wavelength. ### Claim 16 (depends on 13) The single longitudinal-mode laser of claim 13, wherein the first wave plate has a first slow axis substantially perpendicular to the first fast axis and the light propagation direction, wherein the second wave plate has a second slow axis substantially perpendicular to the second fast axis and the light propagation direction. ### Claim 17 (depends on 13) The single longitudinal-mode laser of claim 13, wherein the birefringent gain medium, the first wave plate and the second wave plate are configured to produce the lasing light in a single longitudinal mode when the pump light has a pump power between a threshold pump power and a maximum pump power that is at least 20 times of the threshold pump power. ### Claim 18 (depends on 17) The single longitudinal-mode laser of claim 17, wherein the threshold pump power is below 50 mW, and wherein the maximum pump power is more than 1000 mW. ### Claim 19 (depends on 17) The single longitudinal-mode laser of claim 17, wherein the output laser has a power more than 500 mW when the pump power is at about 1000 mW. ### Claim 20 (depends on 17) The single longitudinal-mode laser of claim 17, wherein the wavelength of the output laser has a variation smaller than 0.3 nm when the pump power varies from the threshold pump power and the maximum pump power. ### Claim 21 (depends on 13) The single longitudinal-mode laser of claim 13, wherein the birefringent gain medium, the first wave plate and the second wave plate are configured to produce the lasing light in a single longitudinal mode thereby producing the output laser having a wavelength variation less than 0.3 nm over a temperature range from 10° C. to 40° C. ### Claim 22 A single longitudinal-mode laser, comprising: a first mirror; a second mirror, wherein the first mirror and the second mirror define a laser cavity therein, wherein the first mirror is configured to allow a pump light at a pumping wavelength to enter the laser cavity; a first wave plate positioned between the first mirror and the birefringent gain medium, wherein the first wave plate is a quarter wave plate at a lasing wavelength and a whole wave plate at the pumping wavelength, wherein the first wave plate has a first fast axis substantially perpendicular to the light propagation direction, wherein the first fast axis is at a first angle relative to the optical axis of the birefringent gain medium, wherein the first angle is between 30 and 60 degrees; a birefringent gain medium configured to generate a first linearly polarized lasing light at the lasing wavelength along a light propagation direction in response to the pump light, wherein the birefringent gain medium has an optical axis substantially perpendicular to the light propagation direction, wherein the first linearly polarized lasing light has a first linear polarization parallel to the optical axis of the birefringent gain medium; and a second wave plate positioned between the birefringent gain medium and the second mirror, wherein the second wave plate has a second fast axis substantially perpendicular to the light propagation direction and to the first fast axis, wherein the second wave plate is configured to produce a first circularly polarized lasing light, wherein the second mirror is configured to reflect the first circularly polarized lasing light to produce a second circularly polarized lasing light and to output at least a portion of the first circularly polarized lasing light out of the laser cavity to form an output laser, wherein the second wave plate is configured to produce a second linearly polarized lasing light having a second linear polarization perpendicular to the optical axis of the birefringent gain medium in response to the second circularly polarized lasing light. ### Claim 23 (depends on 22) The single longitudinal-mode laser of claim 22, wherein there is no linear polarizer positioned within the laser cavity.