CW DUV laser with improved stability

Patent metadata

Field	Value
Publication number	US-10044166-B2
Application number	US-201615335266-A
Country	US
Kind code	B2
Filing date	Oct 26, 2016
Priority date	Jun 11, 2013
Publication date	Aug 7, 2018
Grant date	Aug 7, 2018

Abstract

A deep ultra-violet (DUV) continuous wave (CW) laser includes a fundamental CW laser configured to generate a fundamental frequency with a corresponding wavelength between about 1 μm and 1.1 μm, a third harmonic generator module including one or more non-linear optical (NLO) crystals that generate a third harmonic and an optional second harmonic, and a fifth harmonic generator. The fifth harmonic generator module includes a cavity resonant at the fundamental frequency, and combines the fundamental frequency with the third harmonic in a first NLO crystal to generate a fourth harmonic, then combines the fourth harmonic with unconsumed fundamental frequency in a second NLO crystal to generate the fifth harmonic. One or more lenses are used to focus the third and fourth harmonics in the first and second NLO crystals, respectively.

First claim

The invention claimed is:

1. A deep ultra-violet (DUV) continuous wave (CW) laser comprising:
a fundamental CW laser configured to generate a fundamental frequency with a corresponding wavelength between 1 μm and 1.1 μm;
a third harmonic generator module configured to generate a third harmonic using a first portion of the fundamental frequency;
a fifth harmonic generator module comprising:
a plurality of optical elements forming a cavity resonant at the corresponding wavelength of the fundamental frequency, the plurality of optical elements being configured to operably couple the third harmonic and a second portion of the fundamental frequency in the cavity, and
first and second NLO crystals operably disposed in the cavity and collectively configured to generate a fifth harmonic by combining the second fundamental frequency portion and the third harmonic,

wherein a first optical element of said plurality of optical elements comprises a dichroic curved mirror configured to reflect the second fundamental frequency portion along the cavity light path and to pass the third harmonic into the cavity such that the third harmonic overlaps with the second fundamental frequency portion in the first NLO crystal, and
wherein the fifth harmonic generator module further comprises one or more first lenses configured to focus the third harmonic inside the first NLO crystal.

2. The laser of claim 1 ,
wherein a second optical element of said plurality of optical elements forming said cavity comprises an input coupler, and
wherein the fifth harmonic generator module further comprises mode matching lenses configured to focus and couple the second fundamental frequency portion in the cavity by way of the input coupler.

3. The laser of claim 1 , wherein the first NLO crystal is configured to generate a fourth harmonic by summing said second fundamental frequency portion and said third harmonic.

4. The laser of claim 3 , wherein the fifth harmonic generator module further comprises one or more second lenses disposed in the cavity light path between the first NLO crystal and the second NLO crystal, and configured to focus an unconsumed portion the second fundamental frequency portion and the fourth harmonic inside the second NLO crystal such that the fifth harmonic is generated by frequency summation of the unconsumed fundamental frequency portion and the fourth harmonic.

5. The laser of claim 4 , wherein the one or more second lenses comprises one or more achromatic lenses.

6. The laser of claim 1 , wherein the first NLO crystal comprises one of CLBO, CBO, LBO, LB4 and BBO.

7. The laser of claim 1 , wherein the second NLO crystal comprises one of CLBO, LB4 and BBO.

8. A deep ultra-violet (DUV) continuous wave (CW) laser comprising:
a fundamental CW laser configured to generate a fundamental frequency with a corresponding wavelength between 1 μm and 1.1 μm;
a third harmonic generator module configured to generate a third harmonic using a first portion of the fundamental frequency;
a fifth harmonic generator module comprising:
a plurality of optical elements forming a cavity resonant at the corresponding wavelength of the fundamental frequency, the plurality of optical elements being configured to operably couple the third harmonic and a second portion of the fundamental frequency in the cavity, and

first and second NLO crystals operably disposed in the cavity and collectively configured to generate a fifth harmonic by combining the second fundamental frequency portion and the third harmonic,
wherein the fifth harmonic generator module further comprises a first beam splitter operably disposed in the cavity light path and configured to divert any unconsumed third harmonic passed through the first NLO crystal out of the cavity.

9. A deep ultra-violet (DUV) continuous wave (CW) laser comprising:
a fundamental CW laser configured to generate a fundamental frequency with a corresponding wavelength between 1 μm and 1.1 μm;
a third harmonic generator module configured to generate a third harmonic using a first portion of the fundamental frequency;
a fifth harmonic generator module comprising:
a plurality of optical elements forming a cavity resonant at the corresponding wavelength of the fundamental frequency, the plurality of optical elements being configured to operably couple the third harmonic and a second portion of the fundamental frequency in the cavity, and

first and second NLO crystals operably disposed in the cavity and collectively configured to generate a fifth harmonic by combining the second fundamental frequency portion and the third harmonic,
wherein the fifth harmonic generator module further comprises a second beam splitter configured to transmit along the cavity light path a second unconsumed portion the fundamental frequency passed through the second NLO crystal, and to divert out of said cavity said fifth harmonic and any unconsumed portion of said fourth harmonic.

10. A deep ultra-violet (DUV) continuous wave (CW) laser comprising:
a fundamental CW laser configured to generate a fundamental frequency with a corresponding wavelength between 1 μm and 1.1 μm;
a third harmonic generator module configured to generate a third harmonic using a first portion of the fundamental frequency;
a fifth harmonic generator module comprising:
a plurality of optical elements configured to form a cavity having a bow-tie cavity light path and being resonant at the corresponding wavelength of the fundamental frequency, at least one of said plurality of optical elements being configured to operably couple a second portion of the fundamental frequency and said third harmonic into the cavity,
a first NLO crystal disposed in the cavity light path;
one or more first lenses configured to focus the third harmonic inside the first NLO crystal, wherein the first NLO crystal is configured to combine the second fundamental frequency portion and the third harmonic to generate a fourth harmonic;
a second NLO crystal disposed in the cavity light path; and
one or more second lenses configured to focus the fourth harmonic inside the second NLO crystal, wherein the second NLO crystal is configured such that unconsumed fundamental frequency portion and said fourth harmonic are combined by frequency summation to generate a fifth harmonic,
wherein the fifth harmonic generator module further comprises a first beam splitter operably disposed in the cavity light path and configured to divert any unconsumed third harmonic passed through the first NLO crystal out of the cavity.

11. A method of generating deep ultra-violet (DUV) continuous wave (CW) laser radiation comprising:
generating first and second fundamental frequency portions, each having a fundamental frequency with a corresponding wavelength between 1 μm and 1.1 μm;
converting the first fundamental frequency portion to a third harmonic;
generating a fourth harmonic by focusing the third harmonic inside a first NLO crystal operably disposed in a cavity and configured to perform sum frequency generation of the second fundamental frequency portion and said third harmonic;
generating a fifth harmonic by focusing the fourth harmonic inside a second NLO crystal that is operably disposed in the cavity and configured to perform sum frequency generation of an unconsumed portion of the second fundamental frequency portion and said fourth harmonic; and
diverting the fifth harmonic and an unconsumed portion of the fourth harmonic out of the cavity.

12. The method of claim 11 , wherein generating the fourth harmonic comprises:
utilizing an input coupler to couple the second fundamental frequency portion into the cavity such that the second fu

Assignees

• Kla Tencor Corp

Inventors

• Chuang Yung-Ho
• Lu Xiaoxu
• Fielden John

Classifications

• G02F2203/15

  involving resonance effects, e.g. resonantly enhanced interaction · CPC title

• H01S3/0092 Primary

  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 title

• H01S3/109 Primary

  Frequency multiplication, e.g. harmonic generation · CPC title

• G02F1/3534

  Three-wave interaction, e.g. sum-difference frequency generation (G02F1/3532 takes precedence) · CPC title

• G02F1/3558

  Poled materials, e.g. with periodic poling; Fabrication of domain inverted structures, e.g. for quasi-phase-matching [QPM] · CPC title