Laser rod thermalization

• US 6,414,980 B1
• Filed: 10/12/1999
• Issued: 07/02/2002
• Est. Priority Date: 10/12/1999
• Status: Expired due to Term

• Current Assignee: Coherent Inc (Coherent Corp.)
• Original Assignee: Coherent Inc (Coherent Corp.)
• Inventors: Wang, Charles Xiaoyi, Hicks, Acle V., Rea, Edward C. Jr.
• Primary Examiner(s): Ip, Paul
• Assistant Examiner(s): ZAHN, JEFFREY N
• Application Number:
  US09/416,354
• Time in Patent Office: 994 Days
• Field of Search: 372/92, 372/93
• US Class Current: 372/92
• CPC Class Codes: B33Y 30/00 Apparatus for additive manufacturing; Details thereof or accessories therefor
• CPC Class Codes: G02F 1/37 for second-harmonic generation G02F1/3532 takes precedence
• CPC Class Codes: H01S 3/07 consisting of a plurality of parts, e.g. segments H01S3/067 takes precedence
• CPC Class Codes: H01S 3/08072 Thermal lensing or thermally induced birefringence; Compensation thereof
• CPC Class Codes: H01S 3/10038 Amplitude control
• CPC Class Codes: H01S 3/10046 Pulse repetition rate control H01S3/11 takes precedence
• CPC Class Codes: H01S 3/117 using intracavity acousto-optic devices

Abstract

A method for operating an extracavity frequency-converted solid-state laser for performing a laser processing operation is disclosed. The laser has a laser-resonator including an optically-pumped gain-medium. The resonator is configured to compensate for a predetermined range of thermal lensing in the gain-medium. An optically-nonlinear crystal located outside the resonator converts fundamental laser radiation delivered by the resonator into frequency converted radiation. The laser processing operation is performed by a train of pulses of the frequency-converted radiation having sufficient power to perform the processing operation. The power of frequency-converted radiation is dependent on delivery parameters of the laser radiation from the laser-resonator. The laser is operated in a manner which provides that the resonator delivers effectively the same average power of fundamental laser radiation before and during the laser processing operation. This provides that thermal-lensing in the gain-medium is within the predetermined range before and during a laser processing operation. Delivery parameters of the laser radiation before and during the processing operation are varied such that power of frequency-converted radiation generated before the processing operating is insufficient to perform a laser processing operation.

Claims

1. A method for operating laser for performing a laser processing operation, the laser having a laser-resonator including a gain-medium and one or more-optically nonlinear crystals located outside the resonator for converting laser radiation delivered by the resonator into frequency converted radiation, the power of the frequency-converted radiation being dependent on delivery parameters of the laser radiation from the laser-resonator, the gain-medium exhibiting a thermal-lensing effect on being optically pumped, said thermal-lensing being dependent on the difference between the power of the optical pumping and the average power of laser radiation delivered by the laser resonator, and with the resonator being configured to compensate for a predetermined range of the thermal-lensing, the method comprising the steps of:

(a) during the following steps, continuously optically pumping the gain medium at essentially constant power;

(b) providing a Q-switch in the resonator for operating the laser to deliver laser radiation in response to said continuous optical pumping;

(c) operating the laser via the Q-switch to deliver laser radiation to the one or more optically-nonlinear crystals in a first mode with delivery parameters thereof being such that frequency-converted radiation generated therefrom has insufficient peak power to perform the laser processing operation;

(d) following step (c), operating the laser via the Q-switch to deliver laser radiation to the one or more optically-nonlinear crystals in a second mode in the form of a train of pulses with delivery parameters thereof being such that pulses in a train of pulses of frequency-converted radiation have sufficient peak power to perform the laser processing operation; and

(e) during steps (c) and (d) operating the laser via the Q-switch such that the difference between optical pumping power and average power of the laser radiation delivered by the laser resonator provide that the thermal-lensing effect is within the compensated range.

2. The method of claim 1, wherein laser radiation delivered in step (c) is CW radiation.

3. The method of claim 1, wherein laser radiation delivered in step (c) is in the form of a train of pulses, and the pulses-repetition rate of pulses in step (c) is greater than the pulse-repetition rate of pulses in step (d).

4. The method of claim 1, wherein steps (c), (d) and (e) are repeated a plurality of times, whereby the laser delivers repeated trains of pulses of frequency converted radiation of sufficient peak power to perform the laser processing operation with frequency converted radiation having insufficient power to perform the laser processing operation being delivered between said repeated trains of pulses.

5. A method for performing a laser processing operation, comprising the steps of:

(a) providing a laser resonator including a solid-state gain medium, said solid-state gain-medium exhibiting a thermal-lensing effect on being optically pumped, said thermal lensing effect being dependent on the difference between the power of said optically pumping and average power of the laser radiation extracted from said gain-medium;

(b) during the following steps continuously optically pumping the gain medium at an essentially constant power;

(c) providing a Q-switch for operating the laser resonator to deliver laser radiation in response to said continuous optical pumping;

(d) directing the laser radiation into one or more-optically nonlinear crystals located outside the resonator for converting laser radiation delivered by the resonator into frequency converted radiation, the power of the frequency-converted radiation being dependent on delivery parameters of the laser radiation from the laser-resonator;

(e) operating the laser resonator via said Q-switch to deliver laser radiation to said one or more optically nonlinear crystals in a first mode with delivery parameters thereof being such that frequency-converted radiation generated therefrom has insufficient peak power to perform the laser processing operation;

(f) following step (e) operating the laser via said Q-switch to deliver laser radiation to said one or more optically nonlinear crystals in a second mode in the form of a train of pulses with delivery parameters thereof being such that pulses in a train of pulses of frequency-converted radiation generated therefrom have sufficient peak power to perform the laser processing operation;

(g) during steps (e) and (f) operating the laser such that the difference between optical pumping power and average power of the laser radiation provide that the thermal-lensing effect remains within a predetermined range; and

(h) controlling a delay time between steps (e) and (f), whereby all pulses delivered in step (f) have about the same peak power.

6. The method of claim 5, wherein laser radiation delivered in step (e) is CW radiation.

7. The method of claim 5, wherein laser radiation delivered in step (e) is in the form of a train of pulses, and the pulses-repetition rate of pulses in step (e) is greater than the pulse-repetition rate of pulses in step (f).

8. The method of claim 5, wherein steps (e), (f), and (g) are repeated a plurality of times, whereby the laser delivers repeated trains of pulses of frequency converted radiation of sufficient peak power to perform the laser processing operation, with frequency-converted radiation having insufficient power to perform the laser processing operation being delivered between said repeated trains of pulses.

9. The method of claim 8, wherein independent of the duration of steps (e) and (f) pulses in each of said trains of pulses each have about the same peak power.

10. A method of operating a laser, the laser having a laser-resonator including a gain-medium said gain medium exhibiting thermal lens effects on being optically pumped, said laser resonator including a Q-switch for operating the resonator to generate laser output pulses for treating a workpiece, said method comprising:

during the following steps continuously optically pumping the gain medium at essentially constant power;

operating the Q-switch in a first mode to generate repeated sequences of bursts of output pulses having a peak power sufficient to treat the workpiece; and

operating the Q-switch in a second mode to generate a laser output between said sequences of bursts in order to maintain the thermal lens effects in the gain medium substantially similar to when the bursts are being generated during the first mode, and wherein the laser output during the second mode has a peak power insufficient to treat the workpiece.

11. A method as recited in claim 10, wherein when said Q-switch is operated in the second mode, the output of the laser is in a continuous form.

12. A method as recited in claim 10, wherein when said Q-switch is operated in the second mode, the output of the laser is in a pulsed form.

13. A method as recited in claim 12, wherein the repetition frequency of the pulses is higher in the second mode than in the first mode.

14. A method as recited in claim 10, wherein the output pulses are directed through one or more nonlinear crystals for increasing the frequency thereof prior to treating the workpiece.

15. A method as recited in claim 10, wherein each of the output pulses generated during the first mode have substantially the same peak power.