# US 10,312,659 B1 · Controlling laser beam parameters by crystal shifting

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- Number: US 10,312,659 B1
- Document ID: US10312659B1
- Status: Granted
- Kind: B1
- Application number: 15/926,178
- Filed: 2018-03-20
- Granted: 2019-06-04
- Earliest claimed: 2018-03-20
- Assignees: Coherent LaserSystems GmbH & Co. KG
- Applicants: Coherent LaserSystems GmbH & Co. KG
- Inventors: Guenter Hollemann; Axel Kneip
- Web page: https://patentgrep.com/patent/US10312659B1

## CPC

- H01S 3/13: Stabilisation of laser output parameters, e.g. frequency or amplitude
- G01J 1/4257: {applied to monitoring the characteristics of a beam, e.g. laser beam, headlamp beam (monitoring arrangements for lasers in general H01S3/0014)}
- G01J 1/429: {applied to measurement of ultraviolet light (using counting tubes G01T)}
- G01N 21/8806: {Specially adapted optical and illumination features}
- G02F 1/3525: {Optical damage}
- G02F 1/353: {Frequency conversion, i.e. wherein a light beam is generated with frequency components different from those of the incident light beams}
- H01S 3/0014: {Monitoring arrangements not otherwise provided for (photometry G01J1/00, e.g. G01J1/4257; radiation pyrometry G01J5/00; measuring coherence of light G01J9/00; measuring wavelength of light G01J9/00, e.g. G01J9/0246; measuring optical pulses G01J11/00; calorimetrically measuring power of laser beams G01K17/003)}
- 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)}
- G01J 2001/4261: {Scan through beam in order to obtain a cross-sectional profile of the beam}
- G01N 21/9501: {Semiconductor wafers (manufacturing processes per se of semiconductor devices implementing a measuring step H10P74/20)}
- G01N 21/956: Inspecting patterns on the surface of objects {(contactless testing of electronic circuits G01R31/308; testing currency G07D; manufacturing processes per se of semiconductor devices implementing a measuring step H10P74/20)}
- G01N 2021/8835: {Adjustable illumination, e.g. software adjustable screen}
- 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)}
- 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
- G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N)
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)
- G02F: OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS

## Abstract

This disclosure provides methods and apparatuses which advantageously stabilize beam parameters and elongate crystal lifetime. In one aspect, a UV laser apparatus includes a non-linear crystal, a laser source, a beam-crystal displacer, a beam parameter monitor, and a laser control unit. The laser source directs a source beam to the non-linear crystal to produce a UV beam and the beam-crystal displacer shifts the non-linear crystal relative to the source beam at a plurality of shift speeds. The beam parameter monitor measures the UV beam and outputs a measurement of a beam parameter. The laser control unit: receives the measurement; determines, based on the measurement, an adjustment in shift speed that steers the beam parameter toward a target value; and outputs the adjustment to the beam-crystal displacer.

## Claims

### Claim 1

A UV laser apparatus comprising:
a non-linear crystal;
a laser source configured to direct a source beam to the non-linear crystal to produce a UV beam;
a beam-crystal displacer configured to shift the non-linear crystal relative to the source beam at a plurality of shift speeds;
a beam parameter monitor configured to measure the UV beam and output a measurement of a size or propagation parameter of the UV beam; and
a laser control unit configured to
receive the measurement,
determine, based on the measurement, an adjustment in shift speed to steer the monitored parameter toward a target value; and
output the adjustment to the beam-crystal displacer.

### Claim 2 (depends on 1)

The apparatus of claim 1, wherein the non-linear crystal degrades during an exposure to the source beam and at least partially recovers after the exposure to the source beam.

### Claim 3 (depends on 1)

The apparatus of claim 1, wherein the beam-crystal displacer is configured to shift the non-linear crystal so that the source beam repeatedly traverses a path.

### Claim 4 (depends on 3)

The apparatus of claim 3, wherein a time between irradiations of a spot on the path is at least 20 times longer than an irradiation time of the spot.

### Claim 5 (depends on 1)

The apparatus of claim 1, wherein the beam-crystal displacer is configured to shift the non-linear crystal so that the source beam traverses a serpentine path.

### Claim 6 (depends on 1)

The apparatus of claim 1, wherein the laser control unit is further configured to, upon receiving a measurement that indicates the size or propagation parameter is above the target value, output an increase in shift speed to the beam-crystal displacer and further configured to, upon receiving a measurement that indicates the size or propagation parameter is below the target value, output a decrease in shift speed to the beam-crystal displacer.

### Claim 7 (depends on 1)

The apparatus of claim 1, wherein the target value of the size or propagation parameter comprises a target range of the size or propagation parameter with an upper threshold and a lower threshold.

### Claim 8 (depends on 7)

The apparatus of claim 7, wherein the laser control unit is further configured to, upon receiving a measurement that indicates the size or propagation parameter is above the upper threshold, output an increase in shift speed to the beam-crystal displacer and is further configured to, upon receiving a measurement that indicates the size or propagation parameter is below the lower threshold, output a decrease in shift speed to the beam-crystal displacer.

### Claim 9 (depends on 1)

The apparatus of claim 1, wherein the beam parameter monitor is configured to continuously measure the UV beam.

### Claim 10 (depends on 9)

The apparatus of claim 9, wherein the laser control unit is configured to continuously output the adjustment to the beam-crystal displacer.

### Claim 11 (depends on 1)

The apparatus of claim 1, wherein the beam-crystal displacer is configured to shift the non-linear crystal so that the source beam repeatedly traverses a path and wherein the shift speed is adjusted at least once while traversing the complete path.

### Claim 12 (depends on 1)

The apparatus of claim 1, wherein the beam parameter monitor is configured to measure the UV beam at a refurbishment interval.

### Claim 13 (depends on 1)

The apparatus of claim 1, wherein the size or propagation parameter is one of beam quality, axial beam waist location, beam divergence, and beam waist diameter.

### Claim 14 (depends on 1)

The apparatus of claim 1, wherein the beam parameter monitor is configured to monitor a process property resulting from the UV beam's interaction with a process object.

### Claim 15 (depends on 1)

The apparatus of claim 1, wherein the beam-crystal displacer is configured to shift the non-linear crystal relative to the source beam by one of continuous shifting, approximately continuous shifting, or step-wise shifting.

### Claim 16 (depends on 15)

The apparatus of claim 15, wherein the beam-crystal displacer is configured to shift the non-linear crystal relative to the source beam by continuous shifting.

### Claim 17

A method for controlling a UV beam, the method comprising:
directing a source beam to a non-linear crystal to produce a UV beam;
shifting the non-linear crystal relative to the source beam at a first shift speed;
measuring a size or propagation parameter of the UV beam;
determining, based on the measured parameter, a second shift speed that steers the parameter toward a target value of the parameter; and
shifting the non-linear crystal relative to the source beam at the second shift speed.

### Claim 18 (depends on 17)

The method of claim 17, wherein the non-linear crystal degrades during an exposure to the source beam and at least partially recovers after the exposure to the source beam.

### Claim 19 (depends on 17)

The method of claim 17, wherein shifting the non-linear crystal comprises shifting the non-linear crystal so that the source beam repeatedly traverses a path on the non-linear crystal.

### Claim 20 (depends on 19)

The method of claim 19, wherein a time between irradiations of a spot on the path is at least 20 times longer than an irradiation time of the spot.

### Claim 21 (depends on 17)

The method of claim 17, wherein shifting the non-linear crystal comprises shifting the non-linear crystal so that the source beam traverses a serpentine path on the non-linear crystal.

### Claim 22 (depends on 17)

The method of claim 17, further comprising:
determining whether the measured parameter is above the target value; and
in response to determining the measured parameter is above the target value, determining the second shift speed, wherein the second shift speed is faster than the first shift speed.

### Claim 23 (depends on 17)

The method of claim 17, further comprising:
determining whether the measured parameter is below the value; and
in response to determining the measured parameter is below the value, determining the second shift speed, wherein the second shift speed is slower than the first shift speed.

### Claim 24 (depends on 17)

The method of claim 17, wherein the target value of the size or propagation parameter comprises a target range of the size or propagation parameter with an upper threshold and a lower threshold.

### Claim 25 (depends on 24)

The method of claim 24, further comprising:
determining whether the measured parameter is above the upper threshold; and
in response to determining the measured parameter is above the upper threshold, determining the second shift speed, wherein the second shift speed is faster than the first shift speed.

### Claim 26 (depends on 24)

The method of claim 24, further comprising:
determining whether the measured parameter is below the lower threshold; and
in response to determining the measured parameter is below the lower threshold, determining the second shift speed, wherein the second shift speed is slower than the first shift speed.

### Claim 27 (depends on 17)

The method of claim 17, wherein measuring the size or propagation parameter comprises continuously measuring the UV beam.

### Claim 28 (depends on 27)

The method of claim 27, further comprising
continuously determining, based on the continuous measurements, additional shift speeds that steer the size or propagation parameter toward the target value; and
shifting the non-linear crystal relative to the source beam at the additional shift speeds.

### Claim 29 (depends on 17)

The method of claim 17, wherein shifting the non-linear crystal comprises shifting the non-linear crystal so that the source beam repeatedly traverses a path on the non-linear crystal, and wherein shifting at the second shift speed comprises shifting at the second shift speed at least once while traversing the complete path.

### Claim 30 (depends on 17)

The method of claim 17, wherein measuring the size or propagation parameter comprises measuring the UV beam at a refurbishment interval.

### Claim 31 (depends on 17)

The method of claim 17, wherein the size or propagation parameter is one of beam quality, axial beam waist position, beam divergence, and beam waist diameter.

### Claim 32 (depends on 17)

The method of claim 17, wherein measuring the size or propagation parameter of the UV beam comprises measuring a process property resulting from the UV beam's interaction with a process object.

### Claim 33 (depends on 17)

The method of claim 17, wherein shifting the non-linear crystal relative to the source beam at a first shift speed comprises shifting the non-linear crystal relative to the source beam by one of continuous shifting, approximately continuous shifting, or step-wise shifting.

### Claim 34 (depends on 33)

The method of claim 33, wherein shifting the non-linear crystal relative to the source beam at a first shift speed comprises continuous shifting of the non-linear crystal relative to the source beam.