CN100442135C - Optical wavelength conversion method, optical wavelength conversion system, program and medium, and laser oscillation system - Google Patents

Abstract

In an optical wavelength converting method in which light from a laser oscillator that oscillates coherent light of an inherent wavelength lambda is employed as incident light, and is made to input to a nonlinear optical crystal, and light having a wavelength of 1/2 lambda is radiated, the wavelength of the incident light is 1000 nm or less, and the peak power density of the incident light is 0.1-10 fold greater than the peak power density that provides the maximum conversion efficiency. The nonlinear optical crystal is heated to and maintained at 200-600 DEG C. An optical wavelength converting method, and a program therefor are provided that achieves high conversion efficiency stably using an nonlinear optical crystal, enabling manufacture of an all solid state ultraviolet laser oscillator that is durable with respect to practical application. Prescribed fundamental waves are input to a first crystal and a second crystal sequentially. The first crystal has a higher bulk damage threshold value with respect to the fundamental waves than that of the second crystal. The second crystal has a higher effective nonlinear constant with respect to the fundamental waves than that of the first crystal. An optical wavelength converting method, optical wavelength converting system and a laser oscillating system are provided that enable high power second harmonics to be obtained with good efficiency.

Description

Optical wavelength conversion method, optical wavelength conversion system, program and medium and laser oscillation system

Technical field

The present invention relates to be used for optical wavelength conversion method, optical wavelength conversion system, program and the medium of laser oscillator.Be specifically related to nonlinear optical crystal, particularly to monocrystalline lithium pyroborate (Li as the second harmonic generating device ₂B ₄O ₇, hereinafter referred to as " LB4 ") and the incident coherent light, it is transformed to optical wavelength conversion method, optical wavelength conversion system, program and the medium of outgoing after 1/2 wavelength light.And, the invention still further relates to and can obtain high-power second harmonic, third harmonic and other and optical wavelength conversion method, optical wavelength conversion system and laser oscillation system frequently expeditiously.

Background technology

As using, has the advantage that can increase recording density with short wavelength's laser to the record data of recording medium or from the light source of recording medium sense data.And, be used for man-hour that adds of material, have little and the advantage that can retrofit of heat affecting.And, in the photoetching (lithography) of medical light source or VLSI (very large scale integrated circuit) with the laser that also is suitable for the short wavelength in the light source etc.

So, the laser that in field miscellaneous, needs the short wavelength.Therefore, industry is expected small-sized, the light weight of outgoing short wavelength laser stably, long-life light source.

But, also do not have the suitable sources of the following wavelength light of outgoing 500nm all the time.For example, though but know with the semiconductor laser outgoing and reach laser about wavelength 400nm, there is the low-down problem of output power.

The laser instrument of known short wavelength and big output power has excimer laser.Excimer laser is realized first in the method for the usefulness electron beam excitation liquid xenons (Xe) such as Basov of the Soviet Union in 1970, and in 1976, also success was in the vibration of the mode of using discharge excitation.The excimer laser of discharge excitation mode repeats on the oscillating laser in ultraviolet pulse, amplifies the ultraviolet light that ArF (193nm), KrF (248nm), XeCl compounds such as (308nm) are launched with optical resonator, and extracts out as laser.Excimer laser is expected ablation (ablation) processing of macromolecular material, the surperficial people that are applied as that reform aspects such as processing, blaze note, film making, medicine manufacturing, isotopic separation.But excimer laser for example is repeat number hundred pps (pulse per second: during pulse/sec) pulsed laser, per 10 ^-2Only produce 10 second ^-9The pulsed light of second, the fluorescent lifetime of comparing laser instrument with interval (interval) is obviously short, therefore, has problems in processing on application or the film forming procedure.And also there are problems such as life-span weak point, the miniaturization difficulty of laser aid, the maintenance property of its dielectric gas is poor, operating cost height, use toxic gas in excimer laser.In a word, current ambient temperature down the practicability of the long-time stable semiconductor laser that produces ultraviolet region light etc. still be unrealized.

So the research that nonlinear optical elements such as (SHG:secondary harmonic-wavegeneration) element in recent years second harmonic are taken place is active all the more.Because the SHG element produces 1/2 wavelength light of lambda1-wavelength, for example, can produce the light of ultraviolet region from the laser of infrared region, the commercial value of using in each field is very big.

Known use crystal as Wavelength conversion element, disclosed KTP (KTiOPO in the flat 3-65597 communique of Japanese Patent Application Laid-Open is for example arranged as SHG element etc. ₄), the spy opens disclosed BBO (β-BaB in the clear 63-279231 communique ₂O ₄), CLBO (CsLiB ₆O ₁₀), LBO (LiB ₃O ₅), KDP (KH ₂PO ₄).

But, not only be difficult to carry out the maximization of crystal with the Wavelength conversion element of KTP, and there is variations in refractive index in crystals.Therefore, cause phase matching angle difference, therefore, have the shortcoming that is difficult to realize high-precision Wavelength conversion element even the refractive index of the KTP element that gets off from a crystal-cut is also different.And, form easily in the crystal of KTP in so-called " nest ", therefore, there is the shortcoming that is difficult to provide in batches high-quality KTP.

And,, have the problems such as output power instability that cause because of moisture-proof, anti-damage from laser, two-photon absorption etc. though adopt the inverting element of BBO, CLBO to have high conversion efficiency.

And using the shortest SHG wavelength (frequency multiplication) of the inverting element of LBO is 277nm, and the wavelength conversion scope is narrower.Therefore, can not produce 4 frequencys multiplication (266nm) of Nd:YAG laser instrument.Also there is the shortcoming that can not form large-scale crystal.

And the inverting element of using KDP does not match owing to absorb the influence generation phase place of heat, if not the low-repetition-frequency below the 100Hz just can not use down when repetition frequency is high.Its damage threshold is extremely low under high repetition frequency.Therefore, be difficult to be used on repetition frequency industrial (or industry is used) laser oscillator above 1KHz.

Therefore, applicant of the present invention had before proposed the LB4 (Li with monocrystalline ₂B ₄O ₇) as the Wavelength conversion method (Japanese patent application laid is willing to flat 8-250523 number) of inverting element.

This monocrystalline LB4 is to the wavelength transparency height of wide region, and damage from laser is little.And, make high-quality and large-scale crystal easily.In addition, its processability is good, hygroscopy is little and good operability, and the life-span is long.

Therefore, adopt LB4 can obtain long-term stable operation, the life-span is long, processability is rich, volume is little, in light weight, optical transform component that price is low.

The conversion efficiency of Wavelength conversion element mainly allows that by the so-called angle of the nonlinear optical constant of crystal or phase matching the intrinsic physical parameter of the crystal of width determines.But above-mentioned monocrystalline LB4 exists conversion efficiency to be lower than the shortcoming of BBO or CLBO.Therefore, be considered to also improper with the low monocrystalline LB4 of conversion efficiency as emission ultraviolet region light wavelength inverting element.

Obtain the high emergent light of average output power in order to improve low conversion efficiency, can adopt various technical methods.All the time, for example adopt and assemble the method that incident light improves the peak power density of incident light by lens, increase the method for crystal length, use the method for a plurality of Wavelength conversion crystals, and use laser oscillator as the method for light source etc. with the little high quality beam characteristic of high-output power and light diffusibleness.

But, improve conversion efficiency with this technical method and have following limitation.

At first, assemble in the method for peak power density that incident light improves incident light, can not unrestrictedly improve peak power density, need to consider the damage from laser that causes because of incident light by lens.

In other words, on the end face of the crystal element of Wavelength conversion element, the antireflection film used of coated with antireflection usually, but the anti-damage from laser of this antireflection film is generally not enough, and may damaged when the peak power density of incident light is too high.And,, may cause the dielectric breakdown of crystal element self with the occasion of higher peak power density incident.Therefore, to the peak power density of incident light, have to consider to contain antireflection film characteristic Wavelength conversion element integral body laser damage threshold and limited.

And, when obtaining high conversion efficiency along with the raising of the peak power density of incident light, also exist nonlinear optical crystal the problem of intrinsic so-called two-photon absorption.This is, along with the two-photon absorption of crystal self, is formed centrally annular cavity in outgoing beam pattern (beam pattem), makes the unsettled phenomenon of output stage.Since two-photon absorption with square the strengthening pro rata of the beam intensity of emergent light, particularly the influence of the heating of the crystals that causes because of absorption in the high beam center portion of intensity is very big, refractive index is changed and phase matching is damaged.

Have again, all the time, in order to protect nonlinear crystal not to be subjected to influence of moisture or to carry out temperature variant phase matching, with the nonlinear optical crystal heating and remain on about 40～200 ℃.

And when assembling incident light with lens, the diffusibleness of incident beam increases, and therefore, can surpass the angle permissible range of phase matching, reduces conversion efficiency on the contrary.

In the method that increases crystal length, the angle of phase matching allows that the absorption of narrowed width and crystal increases, and when surpassing certain-length, as seen has conversion efficiency to be tending towards saturated tendency gradually during owing to the crystal length lengthening.And, when increasing the disposal of crystal length, exist beam pattern to produce the problem of distortion.In a word, the method for not talkative increase crystal length is an effective method.

And the method for using a plurality of Wavelength conversion crystals is to make the light beam that does not pass crystals incide next crystal and the method utilized again with making wavelength conversion.According to the method, not only improve conversion efficiency, can expect that also the output power that is caused by the wavelength conversion interference of light effect that a plurality of crystal produce increases.But, in the time of according to the method, exist the big or beam diameter of the light diffusibleness of incident light hour can not obtain the problem of sufficient interference effect.

In addition, in the method for the laser oscillator with high-quality beam characteristics,, preferably use high-output power and the little light beam of light diffusibleness for improving conversion efficiency really as light source.But such oscillator is difficult to low-cost the manufacturing.

As mentioned above, about other problem,, obtain high-power second harmonic etc. and method prematurity still frequently expeditiously though known have various nonlinear optical crystals as inverting element.

In other words, in order to obtain high-power second harmonic etc. and frequently, the first, need to use the inverting element that can obtain high conversion efficiency.The second, in order to carry out the conversion of high-power incident light, need to use the inverting element that incident light is had high traumatic resistance.

But the traumatic resistance of nonlinear optical crystal that generally has high conversion efficiency is lower, and the nonlinear optical crystal with high damnification resistant has the low tendency of conversion efficiency.Therefore, fail to obtain to have simultaneously the enough conversion efficiencys and the nonlinear optical crystal of traumatic resistance.

In view of the above problems, problem of the present invention is: provide and use nonlinear optical crystal, monocrystalline lithium pyroborate LB4 for example makes optical wavelength conversion method, optical wavelength conversion system, program and the medium (first problem) of stably reaching high conversion efficiency and durable total solids Ultra-Violet Laser oscillator.

And, another problem of the present invention is: provide the restrictive condition to available nonlinear optical crystal to be replenished, can high-level efficiency obtain high-power second harmonic etc. and optical wavelength conversion method, optical wavelength conversion system and laser oscillation system (second problem) frequently.

Disclosure of an invention

In order to solve above-mentioned first problem, the invention provides such optical wavelength conversion method, this method is being incident light from the light with the predetermined repetition frequency of the laser oscillator of the coherent light starting of oscillation of natural wavelength λ, make it incide the nonlinear optical crystal of predetermined crystal length, make the light outgoing of 1/2 λ wavelength, it is characterized in that: described incident light wavelength is below the 1000nm, and the peak power density of described incident light is 0.1～10 times of peak power density that maximum conversion efficiency is provided.

And, the invention provides such optical wavelength conversion method, this method makes it incide the monocrystalline lithium pyroborate (Li of predetermined crystal length to be incident light from the light with the predetermined repetition frequency of the laser oscillator of the coherent light starting of oscillation of natural wavelength λ ₂B ₄O ₇), make the light outgoing of 1/2 λ wavelength, it is characterized in that: described incident light wavelength is below the 1000nm, and the peak power density of described incident light is 0.1～10 times of the optimum peak power density Pc that provided by following formula (1).

Pc＝α·Rep ^β (1)

(in the formula, Rep: repetition frequency, α and β: constant)

And, the invention provides such optical wavelength conversion system, this system is provided with the laser oscillator with the coherent light starting of oscillation of natural wavelength λ, and be incident light with light from the predetermined repetition frequency of this laser oscillator, make the nonlinear optical crystal of predetermined crystal length of the light outgoing of 1/2 λ wavelength, it is characterized in that: described incident light wavelength is below the 1000nm, and the peak power density of described incident light is 0.1～10 times of peak power density that maximum conversion efficiency is provided.

And, the invention provides such optical wavelength conversion system, this system is provided with the laser oscillator with the coherent light starting of oscillation of natural wavelength λ, and be incident light with the light from the predetermined repetition frequency of this laser oscillator, make the monocrystalline lithium pyroborate (Li of predetermined crystal length of the light outgoing of 1/2 λ wavelength ₂B ₄O ₇), it is characterized in that: described incident light wavelength is below the 1000nm, and the peak power density of described incident light is 0.1～10 times of the optimum peak power density Pc that provided by following formula (1).

Pc＝α·Rep ^β (1)

(in the formula, Rep: repetition frequency, α and β: constant)

The peak power density of incident light in above-mentioned each invention provides 0.1～10 times of peak power density of maximum conversion efficiency, and 0.1～5 times be ideal, preferably 0.5～2 times.

Incident light wavelength in above-mentioned each invention is below the 1000nm, can be 400～800nm, and 400～600nm is comparatively desirable, and 400～550nm is then better, preferably 480～540nm.

And the light diffusibleness of the described incident light in above-mentioned each invention is preferably 0.3～4mrad to be ideal below the 10mrad.

And the time pulsewidth is preferably 1 * 10 to be ideal below the 100nsec ^-3～80nsec.

And peak power density is preferably 1MW/cm ²More than.

The present invention also provides a kind of computing machine that makes to carry out as the functional programs of lower device: the input media of the data set that peak power density and the conversion efficiency by incident light when having accepted to nonlinear optical crystal incident wavelength and be the emergent light of acquisition wavelength 1/2 λ behind the incident light of predetermined repetition frequency of λ constitutes; Store the memory storage of a plurality of described data sets; Calculate the arithmetic unit of the peak power density that maximum conversion efficiency is provided with being stored in a plurality of data sets in the described memory storage; And output is by the output unit of the peak power density that maximum conversion efficiency is provided of arithmetic unit acquisition.

And, the invention provides and can make computing machine carry out as the functional programs of lower device: the input media of the setting value that constitutes by repetition frequency Rep and constant alpha, β when having accepted to nonlinear optical crystal incident the emergent light of acquisition wavelength 1/2 λ behind the incident light of wavelength X; With the setting value of the described input media of input, the arithmetic unit of calculating optimum peak power density based on following formula (1); And output is by the output unit of the optimum peak power density of arithmetic unit acquisition.

Pc＝α·Rep ^β (1)

(in the formula, Rep: repetition frequency, α and β: constant)

And, the invention provides the computer-readable media of the program of being equipped with, this program makes computing machine carry out as the function of lower device: the input media of the data set that peak power density and the conversion efficiency by incident light when having accepted to nonlinear optical crystal incident wavelength and be the emergent light of acquisition wavelength 1/2 λ behind the incident light of predetermined repetition frequency of λ constitutes; Store the memory storage of a plurality of described data sets; Calculate the arithmetic unit of the peak power density that maximum conversion efficiency is provided with being stored in a plurality of data sets in the described memory storage; And output is by the output unit of the peak power density that maximum conversion efficiency is provided of arithmetic unit acquisition.

And, the present invention also provides a kind of computer-readable media that program is housed, and this program makes computing machine carry out as the function of lower device: the input media of the setting value that is made of repetition frequency Rep and constant alpha, β when having accepted to nonlinear optical crystal incident the emergent light of acquisition wavelength 1/2 λ behind the incident light of wavelength X; With the setting value of the described input media of input, the arithmetic unit of calculating optimum peak power density based on following formula (1); And output is by the output unit of the optimum peak power density of arithmetic unit acquisition.

Pc＝α·Rep ^β (1)

(in the formula, Rep: repetition frequency, α and β: constant)

In addition, as computer-readable media of the present invention, can adopt various medium such as hard disk, flexible plastic disc, CD-ROM, semiconductor memory, DVD.

And, for solving above-mentioned first problem, the invention provides a kind of optical wavelength conversion method, this method is being incident light from the light with the laser oscillator of the coherent light starting of oscillation of natural wavelength λ, make it incide nonlinear optical crystal, make 1/2 λ wavelength light outgoing, it is characterized in that: with the heating of described nonlinear optical crystal and remain on 200～600 ℃.

The present invention also provides a kind of optical wavelength conversion system, this system is provided with the laser oscillator with the coherent light starting of oscillation of natural wavelength λ, with the light from this laser oscillator is incident light, make the nonlinear optical crystal of 1/2 λ wavelength light outgoing, and with the heating of this nonlinear optical crystal and remain on 200～600 ℃ heating arrangement.

In above-mentioned each invention, heating and the temperature range that keeps be 200～400 ℃ then better.

And, in above-mentioned each invention the wavelength coverage of incident light can be for 1000nm below, 400～800nm is more satisfactory, 400～600nm is then better, preferably 480～540nm.

In above-mentioned each invention, the light diffusibleness of described incident light is below the 10mrad, to be preferably 0.3～4mrad.

And the time pulsewidth is below the 100nsec, but is preferably 1 * 10 ^-3～80nsec.

Also have, peak power density is preferably 1MW/cm ²More than.

For solving above-mentioned first problem, the present invention also provides a kind of optical wavelength conversion method, and this method makes it incide monocrystalline lithium pyroborate (Li to be incident light from the light with the laser oscillator of the coherent light starting of oscillation of natural wavelength λ ₂B ₄O ₇), make 1/2 λ wavelength light outgoing, it is characterized in that: with the heating of described monocrystalline lithium pyroborate and remain on 50～600 ℃.

And the present invention also provides a kind of optical wavelength conversion system, and this system is provided with the laser oscillator with the coherent light starting of oscillation of natural wavelength λ, is the monocrystalline lithium pyroborate (Li that incident light makes 1/2 λ wavelength light outgoing with the light from this laser oscillator ₂B ₄O ₇), and with the heating of described monocrystalline lithium pyroborate and remain on 50～600 ℃ heating arrangement.

In above-mentioned each invention, heating and the temperature range that keeps be 100～400 ℃ then better.

And, in above-mentioned each invention the incident light wavelength can be for 1000nm below, but 400～800nm is more satisfactory, then better at 400～600nm, 480～540nm preferably.

And in above-mentioned each invention, the light diffusibleness of described incident light is below the 10mrad, but is preferably 0.3～4mrad.

And the time pulsewidth is below the 100nsec, but is preferably 1 * 10 ^-3～80nsec.

Have, peak power density is preferably 1MW/cm again ²More than.

For solving above-mentioned second problem, the invention provides a kind of optical wavelength conversion method, this method incides first nonlinear optical crystal and second nonlinear optical crystal successively with the first-harmonic of predetermined wavelength and time pulsewidth, produce the second harmonic of described first-harmonic, it is characterized in that: the body corresponding to described first-harmonic of described first nonlinear optical crystal damages (bulk damage) threshold value greater than described second nonlinear optical crystal, and effective nonlinear constant that the second harmonic for described first-harmonic of described second nonlinear optical crystal takes place is greater than described first nonlinear optical crystal.

And, the present invention also provides a kind of optical wavelength conversion method, this method incides first nonlinear optical crystal and second nonlinear optical crystal successively with the first-harmonic of predetermined wavelength and time pulsewidth and the second harmonic of described first-harmonic, produce the third harmonic of described first-harmonic, it is characterized in that: described first nonlinear optical crystal corresponding to the body damage threshold of described second harmonic greater than described second nonlinear optical crystal, and effective nonlinear constant that the third harmonic for described first-harmonic of described second nonlinear optical crystal takes place is greater than described first nonlinear crystal.

The present invention also provides a kind of optical wavelength conversion method, this method incides first nonlinear optical crystal and second nonlinear optical crystal successively with the first fundamental wave of predetermined wavelength and time pulsewidth and the second fundamental wave of predetermined wavelength and time pulsewidth, produce described first fundamental wave and second fundamental wave and frequently, it is characterized in that: described first nonlinear optical crystal corresponding to the body damage threshold of described first fundamental wave greater than described second nonlinear optical crystal, and described second nonlinear optical crystal for from described first fundamental wave and second fundamental wave and take place frequently living effective nonlinear constant greater than described first nonlinear optical crystal.

The present invention also provides a kind of optical wavelength conversion system, this system is provided with first nonlinear optical crystal that produces second harmonic because of the first-harmonic incident of predetermined wavelength and time pulsewidth, and second nonlinear optical crystal that produces the second harmonic of described first-harmonic because of emergent light incident from this first nonlinear optical crystal, it is characterized in that: described first nonlinear optical crystal corresponding to the body damage threshold of described first-harmonic greater than described second nonlinear optical crystal, and effective nonlinear constant that the second harmonic for described first-harmonic of described second nonlinear optical crystal takes place is greater than described first nonlinear optical crystal.

The invention provides a kind of optical wavelength conversion system, this system is provided with first nonlinear optical crystal that produces third harmonic because of the second harmonic incident of the first-harmonic of predetermined wavelength and time pulsewidth and described first-harmonic, and second nonlinear optical crystal that produces described third harmonic because of emergent light incident from this first nonlinear optical crystal, it is characterized in that: described first nonlinear optical crystal corresponding to the body damage threshold of described second harmonic greater than described second nonlinear optical crystal, and effective nonlinear constant that the third harmonic for described first-harmonic of described second nonlinear optical crystal takes place is greater than described first nonlinear optical crystal.

And, the present invention also provides a kind of optical wavelength conversion system, this system be provided with that second fundamental wave incident because of the first fundamental wave of predetermined wavelength and time pulsewidth and predetermined wavelength and time pulsewidth produces described first fundamental wave and second fundamental wave with first nonlinear optical crystal frequently, and produce second nonlinear optical crystal described and frequently because of emergent light incident from this first nonlinear optical crystal, it is characterized in that: described first nonlinear optical crystal corresponding to the body damage threshold of described first fundamental wave greater than described second nonlinear optical crystal, and described second nonlinear optical crystal for from described first fundamental wave and second fundamental wave and take place frequently living effective nonlinear constant greater than described first nonlinear optical crystal.

The present invention also provides a kind of laser oscillation system, this system is provided with the fundamental wave oscillator with the first-harmonic starting of oscillation of predetermined wavelength and time pulsewidth, and by the optical wavelength conversion system of incident from the described first-harmonic generation second harmonic of this fundamental wave oscillator, it is characterized in that: described optical wavelength conversion system is an optical wavelength conversion system of the present invention.

And, the invention provides a kind of laser oscillation system, this system is provided with the fundamental wave oscillator with the second harmonic starting of oscillation of the first-harmonic of predetermined wavelength and time pulsewidth and described first-harmonic, and produced the optical wavelength conversion system of third harmonic from the described first-harmonic of this fundamental wave oscillator and described second harmonic by incident, it is characterized in that: described optical wavelength conversion system is an optical wavelength conversion system of the present invention.

And, the present invention also provides a kind of laser oscillation system, this system is provided with the fundamental wave oscillator with the second fundamental wave starting of oscillation of the first fundamental wave of predetermined wavelength and time pulsewidth and predetermined wavelength and time pulsewidth, and by described first fundamental wave and described second fundamental wave generation and frequently the optical wavelength conversion system of incident from this fundamental wave oscillator, it is characterized in that: described optical wavelength conversion system is an optical wavelength conversion system of the present invention.

According to above-mentioned each invention, even the conversion efficiency of first nonlinear optical crystal is low, also can be by second nonlinear optical crystal expeditiously in addition conversion such as the first-harmonic that passes through.And, even it is damaging low that second nonlinear optical crystal fast light causes, also can pass the fast light damaging first high nonlinear crystal that causes, after reducing to the receptible power of second nonlinear optical crystal institute, make it incide second nonlinear optical crystal again by making incident light.

In other words, have different types of nonlinear optical crystal of particular kind of relationship by combination, can realize remedying each other high conversion efficiency shortcoming, whole with high fast light cause damaging.Therefore, can obtain expeditiously high-power second harmonic etc. and frequently.

First nonlinear optical crystal in above-mentioned each invention is preferably monocrystalline lithium pyroborate (Li ₂B ₄O ₇).LB4 (Li ₂B ₄O ₇) though conversion efficiency is low, have extraordinary fast light cause damaging.

When first nonlinear optical crystal had adopted LB4, second nonlinear optical crystal was preferably LiB ₃O ₅(LBO), CsLiB ₆O ₁₀(CLBO), KTiOPO ₄(KTP) or β-BaB ₂O ₄(BBO).

Below, describe with regard to technical meaning of the present invention with reference to experimental result.

The inventor at first tries to achieve the peak power density of incident light that nonlinear optical crystal is the LB4 crystal and the relation between the conversion efficiency from experiment.The result as shown in Figure 1.The condition of the oscillator of used incident light and LB4 crystal as described below in experiment.

At first, the oscillator of incident light has adopted combination Nd:YAG laser instrument and as the structure of the lbo crystal of SHG element.In other words, be from the near infrared light (1064nm) of Nd:YAG laser instrument green laser (532nm) to the incident light of LB4 crystal through frequency multiplication.In addition, in order to the oscillator of the incident light more than the acquisition repetition frequency 5KHz with in order to obtain the oscillator of the incident light below the repetition frequency 100Hz, adopt different oscillators.

Peak power density is that the average output power with incident light obtains divided by repetition frequency, beam area and time pulsewidth.So, in this experiment, adjusted the average output power of incident light by the power of adjusting the exciting light of supplying with the YAG laser instrument.And, adjusted beam diameter (beam area) with convergent lens.

On the other hand, used the LB4 crystal of crystal length as 35mm or 60mm.Have, the sectional area of LB4 crystal does not influence conversion efficiency again, but what mainly use is the LB4 crystal of cross section as 15mm * 15mm.

Among Fig. 1, symbol X ₁The data of (◇ of blacking) expression crystal length 35mm, repetition frequency 1Hz, beam diameter 5.5mm.

Symbol X ₁₀(peak power density is less than 200MW/cm for (of blacking) expression crystal length 35mm, repetition frequency 10Hz, beam diameter 5.5mm or 11mm ²: 11mm, peak power density 200MW/cm ²More than: data 5.5mm).

Symbol X ₁₀₀(peak power density is less than 100MW/cm for (△ of blacking) expression crystal length 35mm, repetition frequency 100Hz, beam diameter 5.5mm or 11mm ²: 11mm, peak power density 100MW/cm ²More than: data 5.5mm).

Symbol Y ₁₀() data of expression crystal length 60mm, repetition frequency 10Hz, beam diameter 11mm.

And, symbol Y ₁₀₀(△) data of expression crystal length 60mm, repetition frequency 100Hz, beam diameter 11mm.

When recording above data, peak power density has been done adjustment, the time pulsewidth has been fixed in 3nsec, average output is changed in the scope of 0～26W.In addition, the light diffusibleness is about 1mrad when beam diameter 5.5mm, be about 0.5mrad when beam diameter 11mm.

Symbols Z ₅The data of (blacking zero) expression crystal length 35mm, repetition frequency 5KHz.When recording this data peak power density has been done adjustment, the time pulsewidth is fixed in 25nsec, 30W is fixed in average output, and beam diameter is changed in the scope of 0.4～1.0mm.In addition, the light diffusibleness is about several mrad (5mrad is following).

Symbols Z ₁₀(◇) data of expression crystal length 35mm, repetition frequency 10KHz.When recording this data peak power density has been done adjustment, the time pulsewidth is fixed in 30nsec, 30W is fixed in average output, and beam diameter is changed in 0.4～1.0mm scope.In addition, the light diffusibleness is about several mrad (5mrad is following).

Generally, by following formula (2) as can be known,, the peak power P of incident light also rises along with increasing conversion efficiency η.

η＝a·tanh ²(b·P ^0.5) (2)

(in the formula, a and b are mainly according to kind of crystalline and the definite constant of crystal length)

Data X as Fig. 1 ₁, X ₁₀, X ₁₀₀Shown in, to the LB4 crystal incident of crystal length 35mm during from the incident light of identical oscillator, the peak power density 100MW/cm of incident light ²Following data, irrespectively consistent with repetition frequency.Therefore, as long as judge it is the interior data of this scope, just can predict rising, in principle according to formula (2), along symbol X along with peak power density ₀The curvilinear motion of expression.If the data in this scope are obtained by symbol X ₀Coefficient a, the b of the curve of expression, then a=32, b=0.085.

As data Z ₅, Z ₁₀Shown in, visible oscillator not simultaneously, even crystal length is 35mm, in full peak power density scope also with curve X ₀Stagger.But,, obtained having and X in the low peak power density ₀The upcurve of roughly the same gradient.In addition, the main cause that staggers is considered to the big cause of light diffusion.

Similarly, as data Y ₁₀, Y ₁₀₀Shown in, the peak power density 50MW/cm of the incident light when adopting the LB4 crystal of crystal length 60mm ²Following data, irrespectively consistent with repetition frequency.Therefore, as long as judge it is the interior data of this scope,, also can predict by symbol Y according to formula (2) in principle even if peak power density is risen ₀The curve of expression.If the data in this scope are obtained by symbol Y ₀Coefficient a, the b of the curve of expression, then a=22, b=0.18.

But, find by this experiment: as data X ₁₀, X ₁₀₀, Y ₁₀₀, Z ₅And Z ₁₀Shown in, when the peak power density of incident light surpasses certain value, the desirable curve X that conversion efficiency is predicted from formula (2) on the contrary ₀, Y ₀Deviate from the phenomenon of reduction.

And these data presentation: repetition frequency is high more, and the peak power density that conversion efficiency changes decline over to is low more.

And, also find the high more tendency of the long more conversion efficiency of crystal length.

As mentioned above, in this experiment, the conversion efficiency the when peak power density of having investigated incident light is changed, the stability of having observed emergent light simultaneously.As a result, just in time conversion efficiency changes reduction into, greatly about the curve X that formula (2) is described ₀, Y ₀Deviate from when producing, found the phenomenon of the unsettled two-photon absorption of output power of emergent light.Make the unsettled phenomenon of this emergent light, before conversion efficiency changes over to lowly, roughly do not observe, after conversion efficiency changes over to lowly, improve peak power density more and just be observed more significantly.

In other words, the inventor finds: the peak power density that provides maximum conversion efficiency under the certain condition of the crystal length of the repetition frequency of laser oscillator and LB4 crystal, be to reach " in fact do not produce so-called two-photon absorption etc. and make the unsettled phenomenon of output power, supply with the optimum value of peak power density of incident light of output power of the emergent light of maximum limit " (hereinafter referred to as " optimum peak power density ").

Then, based on the data X of Fig. 1 ₁, X ₁₀, X ₁₀₀,, after having studied optimum peak power density and how changing, obtain the curve map that is roughly straight line as shown in Figure 2 according to repetition frequency for the situation of crystal length 35mm.The transverse axis of Fig. 2 is represented the repetition frequency of incident light, and the longitudinal axis is represented the peak power density of incident light, and diaxon is logarithmically calibrated scale.

The formula of obtaining about the linear relation of this optimum peak power density Pc is above-mentioned formula (1).

Pc＝α·Rep ^β (1)

(in the formula, Rep: repetition frequency, α and β: constant)

Here, constant alpha, β are mainly according to the kind of the crystal constant definite with crystal length, in the occasion of the LB4 crystal of crystal length 35mm shown in Figure 2, α=576, β=-0.27.And, in occasion α=154, β=-0.25 of the LB4 of crystal length 60mm crystal.

Have again, as data Z ₅, Z ₁₀Shown in, when the light diffusibleness of incident light is changed, can influence conversion efficiency.This is when allowing width owing to the light diffusibleness of incident light above the angle of being determined by the phase-matching condition of LB4 crystal, the loss that can produce conversion efficiency.

But, in this case, by revising the influence that produces by the light diffusibleness, estimate conversion characteristics theoretically after, can try to achieve optimum peak power density.But, the result of Que Rening by experiment, when the light diffusibleness of incident light surpasses 10mrad, about 1/10 of the conversion efficiency when the light diffusibleness that just reduces to incident light is 1mrad.Be difficult to obtain the emergent light of practical level.

Like this, the peak power density of incident light preferably is made as optimum peak power density, but in actual applications, can adopt with optimum peak power density is the peak power density of the certain limit of benchmark.

In other words, the peak power density of incident light is preferably below the optimum peak power density.This is because peak power density during greater than optimum peak power density, the output power instability of emergent light.But two-photon absorption is slowly remarkable after having surpassed optimum peak power, be not to produce immediately to have a strong impact on, therefore, if below 10 times of optimum peak power density then do not hinder actual use.And, if below 2 times of optimum peak power density, then and then can suppress the instability of output power.

In order to obtain high emergent light power expeditiously as far as possible, need be made as more than 0.1 times of optimum peak power density, but be preferably more than 0.5 times.

In addition, consider the life-span that prolongs nonlinear crystal, preferably the peak power density with incident light is made as below 0.8 times of optimum peak power density.Therefore, the peak power density of optimal incident light is 0.5～0.8 times of optimum peak power density.

And, be boundary with optimum peak power density, the unsettled phenomenon of output power when conversion efficiency reduces, wavelength is short more remarkable more, is particularly obviously observed when so-called green glow is transformed to ultraviolet light.Therefore, the present invention is that 1000nm is effective especially when following in the incident light wavelength, but the desired wavelength scope of incident light is 400～800nm, and 400～600nm is then better.

Through the result that the inventor further studies, discovery can increase this optimum peak power density by nonlinear optical crystal being heated and remaining on more than 50 ℃.As mentioned above, all the time, in order to protect nonlinear crystal not to be subjected to influence of moisture or to carry out temperature variant phase matching, heating also keeps nonlinear optical crystal.But,, do not have to heat and kept as the scope more than 200 ℃ of the present invention even if do not reach 200 ℃ in the degree of this occasion heating yet.

As described herein, be heated to the effect of higher temperature with table 1 and Fig. 3 and table 2 and Fig. 4 explanation.

Table 1 is that the average repetition frequency with incident light is decided to be that 10KHz, beam diameter are decided to be 0.25mm, the time pulsewidth is decided to be 28nsec, and the investigation result of the conversion efficiency when only changing the average output power of incident light.And Fig. 3 is the data that table 1 is put down in writing, and average output power, the longitudinal axis that with the transverse axis is incident light is the curve that conversion efficiency is drawn.

Similarly, table 2 is that the average repetition frequency with incident light is decided to be that 10KHz, beam diameter are decided to be 0.35mm, the time pulsewidth is decided to be 28nsec, and the investigation result of the conversion efficiency when only changing the average output power of incident light.And Fig. 4 is the data that table 1 is put down in writing, and average output power, the longitudinal axis that with the transverse axis is incident light is the curve that conversion efficiency is drawn.

As shown in table 2, the average output power of incident light is proportional to the peak power density of incident light.And each table is represented the heating of LB4 and is kept temperature (RT is a room temperature: about 25 ℃) with the temperature (Temp) among the figure.

[table 1]

[table 2]

From table 1 and Fig. 3 as can be known: at ambient temperature, the peak power density that the output power of corresponding incident light is about 14W becomes optimum peak power density.Relative with it, with LB4 heating and when remaining on 60 ℃, the peak power density that is about 17W corresponding to the output power of incident light becomes optimum peak power density.When improving heating again and keeping temperature, do not observe the maximum value of conversion efficiency in measurement range, optimum peak power density also aloft as can be known.

From table 2 and Fig. 4 as can be known: at ambient temperature, be about peak power density (about 57MW/cm of 16W corresponding to the output power of incident light ²) become optimum peak power density.Relative with it, with LB4 heating and when remaining on more than 100 ℃, in measurement range, do not observe the maximum value of conversion efficiency, optimum peak power density is also aloft as can be known.And then as can be known, improving the temperature of heating and the maintenance of LB4 more, its conversion efficiency rises more.

So, can find: along with heating, not only alleviated the influence of the heating that the two-photon absorption of bringing variations in refractive index causes, optimum peak power density is risen, in other words, that has eliminated so-called two-photon absorption in fact makes the unsettled phenomenon of output power, and the peak power density of the stable incident light of output power is risen.

This heating also keeps the effect that produces, in heating and keep temperature high temperature is just remarkable more, but need be more than 200 ℃.Thereby, can alleviate the influence that causes because of two-photon absorption, and eliminate the reduction of conversion efficiency, the phenomenon of the reduction of conversion efficiency is disappeared, obtain stable high-output power.

On the other hand, had better not make heating and maintenance temperature be higher than 600 ℃.When temperature was higher than 600 ℃, the heat-proof device scale that goes out in order to the hot-fluid that prevents the heating arrangement periphery was big, unactual.

Heating also keeps temperature to be preferably below 400 ℃.Even this is because heating and maintenance temperature are higher than 400 ℃, the effect of the influence that reduces two-photon absorption is obviously increased, benefit is little in the practicality.

In addition, conversion efficiency reduces when allowing width by the determined angle of the phase-matching condition of LB4 crystal when the light diffusibleness of incident light surpasses.Therefore, the light diffusibleness of desirable incident light is below the 10mrad, and 0.3～4mrad is then better.

And desirable time pulsewidth is below the 100nsec, and 1 * 10 ^-3～80nsec is then better.

Generally, the high more pulsewidth of repetition frequency is wide more, and pulse energy is also more little.On the contrary, when repetition frequency is hanged down, pulsewidth is narrowed down, pulse energy is increased.Therefore, in the scope that obtains required maximal density, higher limit is determined.

And the peak power density of incident light is preferably 1MW/cm ²More than.In addition, the peak power density of incident light is its upper limit with the scope that the body that crystal does not take place damages (dielectric breakdown) or plated film or crystal end-face damage.

The simple declaration of accompanying drawing

Fig. 1 is the peak power density of expression incident light and the curve map of the relation between the conversion efficiency.

How Fig. 2 has investigated optimum peak power density corresponding to the curve map that draws after the repetition frequency variation.

Fig. 3 is expression about the diagrammatic sketch corresponding to the investigation result of the average output power of the incident light of the heating-up temperature of LB4 crystal and the relation between the conversion efficiency.

Fig. 4 is expression about the diagrammatic sketch corresponding to the investigation result of the average output power of the incident light of the heating-up temperature of LB4 crystal and the relation between the conversion efficiency.

Fig. 5 is the structural drawing of an embodiment of the expression Ultra-Violet Laser oscillator that adopts optical wavelength conversion method of the present invention.

Fig. 6 is the structural drawing of an example according to the computer system of program work of the present invention.

Fig. 7 is the structural drawing of another example according to the computer system of program work of the present invention.

Fig. 8 is the structural drawing of the laser oscillation system of another embodiment of expression the present invention.

Fig. 9 is the curve map how the expression peak power density changes according to first crystal.

Preferred forms of the present invention

Below, describe with regard to embodiments of the present invention with reference to accompanying drawing, but the present invention is not limited to following embodiment.

Fig. 5 is the structural drawing of an embodiment of the expression Ultra-Violet Laser oscillator that adopts optical wavelength conversion method of the present invention.The Ultra-Violet Laser oscillator of Fig. 5 is made of green laser oscillator 10 and wavelength conversion system 20.

The structure of green laser oscillator 10 comprises: the king oscillator 11 that constitutes by the Nd:YAG laser instrument, and will be transformed to the transducer 12 of the green glow (532nm) of frequency multiplication ripple from the first-harmonic (1064nm) of king oscillator 11 outgoing.

And, wavelength conversion system 20 is by constituting with the lower part: in order to isolate from the first-harmonic that passes without wavelength conversion from the separation vessel 21,22 of the green glow of transducer 12 outgoing, is the LB4 crystal holder 23 of incident light by incident by the green glow that separation vessel 21,22 separates, separation is from the prism 24 of the emergent light of LR4 crystal holder 23 outgoing, and in order to absorb the light beam damper (beam damper) 25 of the first-harmonic that separates by separation vessel 21.

Here, in LR4 crystal holder 23, disposed monocrystalline lithium pyroborate LB4 with can satisfying the phase matching angle, be equipped with the heating of this LB4 crystal simultaneously and remain on 600 ± 1 ℃ heating arrangement.

In the Ultra-Violet Laser oscillator of present embodiment,, make green glow be transformed to the ultraviolet light (266nm) that its frequency multiplication ripple is 4 frequency multiplication ripples of first-harmonic by LB4 crystal holder 23.Then, will be extracted out by the ultraviolet light of wavelength conversion with 24 on prism.

At this moment, the optimum peak power density of LB4 crystal holder 23 becomes than value bigger when the normal temperature state that does not heat uses as usual.In addition, the peak power density that incides the green glow of LB4 crystal holder 23 from separation vessel 22 is 0.5～2 times of this optimum peak power density.

According to present embodiment, optimum peak power density is risen, and with this below optimum peak power density, be incident light near the light of the peak power density of optimum peak power density.Therefore, also can obtain stable output power even improve the peak power density of incident light.Therefore, can enough monocrystalline lithium pyroborate LB4, as reaching stable high conversion efficiency, and actual durable total solids Ultra-Violet Laser oscillator.

Fig. 6 is the structural drawing according to an embodiment of the computer system of program work of the present invention.Among Fig. 6, symbol 31 expression arithmetic units, symbol 32 expression input medias, the memory storage of symbol 33 expressions to being stored from the data of input media 32 inputs, symbol 34 expressions show the display of the operation result of arithmetic unit 31, the printer of the operation result of symbol 35 expression printout arithmetic units 31.

In the computer system of present embodiment, under the condition of predetermined repetition frequency, predetermined crystal length, can try to achieve to nonlinear optical crystal incident the optimum peak power density of the wavelength conversion system of the emergent light that obtains wavelength 1/2 λ behind the incident light of wavelength X in the following order.

At first, the data set that constitutes by the peak power density and the conversion efficiency of incident light from input media 32 input.Input method can be artificial input, also can be for importing from the former states such as transmission signal of the determinator of measuring conversion efficiency without staff ground.A plurality of this data sets that are transfused to are stored in memory storage 33.

Then, arithmetic unit 31 is extracted maximum conversion efficiency out from the conversion efficiency data of a plurality of data sets of being stored in memory storage 33.Then, obtain the peak power density of supplying with this maximum conversion efficiency.At this moment, also can from the continuous data of supplying with corresponding to the approximate expression of data set, extract maximum conversion efficiency and maximum power density at that time out.Thereby, can not be subjected to other conversion efficiency etc. error effect ground, obtain the peak power density that maximum conversion efficiency is provided.

By arithmetic unit 31 peak power densities that obtain, that maximum conversion efficiency is provided is that optimum peak power density is presented on the display 34, and by printer 35 printouts.

According to present embodiment, by with reference to being shown and the optimum peak power density of printout, the operator can be under the condition of predetermined repetition frequency, predetermined crystal length, when making the incident light of wavelength X incide the operation of wavelength conversion system of the emergent light that obtains wavelength 1/2 λ behind the nonlinear optical crystal, set suitable peak power density.If the output power with maximum peak power density is directly inputted to laser oscillator, then can control the peak power density of incident light automatically.

Fig. 7 is the structural drawing of another example according to the computer system of program work of the present invention.Among Fig. 7, symbol 41 expression arithmetic units, symbol 42 is represented input medias, and symbol 44 expressions show the display of the operation result of arithmetic units 41, and the printer of the operation result of arithmetic unit 41 is printed and is exported in symbol 45 expressions.

In the computer system of present embodiment, can be under the condition of predetermined repetition frequency, predetermined crystal length, try to achieve the optimum peak power density that the incident light that makes wavelength X incides the wavelength conversion system of the emergent light that obtains wavelength 1/2 λ behind the nonlinear optical crystal in the following order.

At first, the setting value that will be made of repetition frequency Rep and constant alpha, β is manually imported from input media 42.α and the β of this moment try to achieve based on experimental result etc. in advance.

Then, based on following formula (1), arithmetic unit 41 is calculated optimum peak power density.

Pc＝α·Rep ^β (1)

(in the formula, Rep: repetition frequency, α and β: constant)

Optimum peak power density by arithmetic unit 41 is tried to achieve is shown in display 44, and by printer 45 printouts.

According to present embodiment, be shown the also optimum peak power density of printout by reference, the operator can be under the condition of predetermined repetition frequency, predetermined crystal length, and suitable peak power density is set when the incident light that makes wavelength X being incided the operation of wavelength conversion system of the emergent light that obtains wavelength 1/2 λ behind the nonlinear optical crystal.If the output power with maximum peak power density is directly inputted to laser oscillator, then also can control the peak power density of incident light automatically.

Then, with reference to Fig. 8 and Fig. 9, describe with regard to another embodiment of the present invention.

Fig. 8 is the structural drawing of the laser oscillation system of expression present embodiment.The laser oscillation system of Fig. 8 is made of fundamental wave oscillator 50 and optical wavelength conversion system 60.

Fundamental wave oscillator 50 for example is made of separately laser oscillators such as Nd:YAG laser instruments, perhaps constitutes by laser oscillator with to the transducer that the light that vibrates in laser oscillator carries out wavelength conversion.

Optical wavelength conversion system 60 is by constituting with the lower part: in order to isolate from other wavelength light from the separation vessel 61,62 of the first-harmonic of the wavelength X of fundamental wave oscillator 50 outgoing, the first-harmonic that is separated by incident separation vessel 61,62 is first crystal 63 of incident light IO, by second crystal 64 of incident from the emergent light I1 of first crystal 63, separation is from the prism 65 of the emergent light I2 of second crystal 6,4 outgoing, and in order to absorb the light beam damper 66 of the light beyond the fundamental wavelength of separating by separation vessel 61.

Here, first crystal 63 and second crystal 64 are different types of nonlinear optical crystal, and they all are configured to satisfy the phase matching angle corresponding to first-harmonic λ.

Can be used as the nonlinear optical crystal of first crystal 63 or second crystal 64, LB4 (Li is for example arranged ₂B ₄O ₇), KTP (KTiOPO ₄), BBO (β-BaB ₂O ₄), CLBO (CsLiB ₆O ₁₀), LBO (LiB ₃O ₅), KDP (KH ₂PO ₄) etc., in these nonlinear optical crystals, as described below,, select first crystal 63 and second crystal 64 respectively based on the viewpoint of conversion efficiency and traumatic resistance.

At first, in selected two crystal, first crystal 63 is had cause damaging than high fast light of second crystal 64.Specifically, in the occasion that has compared corresponding to the body damage threshold of described first-harmonic, select by the relation that makes first crystal 63 have the body damage threshold bigger than second crystal 64.

This body damage threshold is represented by the threshold value of the peak power density (peak power density of peak value) of the incident light that the body damage is produced.So-called body damage is meant the damage that produces because of incident light destruction crystal chemistry key.

The body damage threshold is low more when short more and time pulsewidth is long more in the incident light wavelength.Wherein, when the body damage threshold of different crystal is compared on a certain wavelength, time pulsewidth, even its magnitude relationship is also constant under the condition of other wavelength, time pulsewidth.

For example, the body damage threshold of main nonlinear optical crystal when wavelength 1064nm, time pulsewidth 1nsec is following value, but its magnitude relationship do not change under other condition yet, becomes following value.

(the body damage threshold when 1064nm, time pulsewidth 1nsec)

LB4：～90GW/cm ²

LBO：～45GW/cm ²

CLBO：～26GW/cm ²

KDP：～14GW/cm ²

BBO：～13GW/cm ²

KTP：～0.6GW/cm ²

(magnitude relationship of body damage threshold)

LB4＞LBO＞CLBO＞KDP＞BBO＞KTP

In addition, photic damage also has the surface damage that produces from plane of crystal except the body damage, and the threshold value of the threshold ratio surface damage of general body damage is big.Therefore, cause the peak power density of the incident light of crystal damage, determine by surface damage usually.But, because the surface damage threshold value is difficult to compare objectively along with the changes such as convergence degree of the having or not of the grinding state on surface, suction, incident light.Therefore, cause in the abrasive evaluation, adopt the body damage threshold the most suitable fast light.

Then, in selected two crystal, make second crystal 64 have the conversion efficiency higher than first crystal 63.Specifically, in the occasion that has compared effective nonlinear constant of described first-harmonic, select by the relation that makes second crystal 64 have effective nonlinear constant bigger than first crystal 63.

So-called effectively nonlinear constant is meant: from the nonlinear constant of nonlinear optical crystal and the effective conversion coefficient of incident angle calculating.But incident angle is chosen to corresponding to incident light wavelength phase matching, therefore, as long as determine the incident light wavelength, just can carry out the comparison of effective nonlinear constant of each crystal substantially.

For example, the effective nonlinear constant of main nonlinear optical crystal at wavelength 1064nm place is following value, and its magnitude relationship is as follows.

(the effective nonlinear constant and the phase matching angle at 1064nm place)

LB4：0.08pm/V、31°

LBO:1.05pm/V, 90 ° (I type)

CLBO:0.47pm/V, 29.4 ° (I type),

0.95pm/V, 42.9 ° (II type)

BBO:1.64pm/V, 22.9 ° (I type)

1.25pm/V, 33.1 ° (II type)

KDP:0.27pm/V, 41.2 ° (I type)

0.34pm/V, 59.2 ° (II type)

KTP:3.24pm/V, 90 ° (II type)

(magnitude relationship of effective nonlinear constant at 1064nm place)

KTP＞BBO＞LBO＞CLBO＞KDP＞LB4

When first crystal 6 of selecting 3 is the LB4 of body damage threshold maximum, can select various nonlinear crystals as second crystal 64, but in the wavelength coverage of effective nonlinear constant greater than effective nonlinear constant of first crystal 63 (LB4) of second crystal 64, need limit the wavelength coverage of incident light and use.Effective nonlinear constant of each crystal is following scope greater than the wavelength coverage of effective nonlinear constant of LB4.

(can obtain the wavelength coverage of the incident light of the effective nonlinear constant bigger) than LB4

LBO：2000～500nm

CLBO：2000～472nm

BBO：1400～409nm

KDP：1300～500nm

KTP：2000～990nm

In the laser oscillation system of present embodiment, it is incident light I0 incident that first crystal 63 is had the first-harmonic of wavelength X.So constitute by the first-harmonic of the second harmonic of wavelength X/2 and the wavelength X of passing without conversion from the emergent light I1 of first crystal 63.At this moment, the peak power density of contained first-harmonic is to deduct the component that is transformed to second harmonic in the peak power density of incident light I0 among the emergent light I1.Therefore, compare, can set the peak power density of incident light I0 than the highland with the occasion that is directly incident on second crystal 64.

In this case, as shown in Figure 9, the effect by first crystal 63 protection, second crystal 64 can not stop in the scope of conversion efficiency of first crystal 63.In other words, shown in Fig. 9 solid line, in the scope of the beam diameter of incident light I0, power density distribution becomes beam center to become maximum peak power density.And, have near the light the beam center of this high peak power density, the easiest damage that causes crystal.On the other hand, has near the light the beam center of this high peak power density, the easiest being transformed.Therefore, shown in the dotted line of Fig. 9, the peak power density of contained first-harmonic has significantly reduction among the emergent light I1 near beam center.Therefore, can significantly reduce the influence that gives second crystal 64.

And, because the conversion efficiency of first crystal 63 is lower, quite a few former state of first-harmonic among the incident light I0 (wavelength X) is passed and is contained in the middle of the emergent light I1, but because the conversion efficiency height of second crystal 64 can obtain high-power second harmonic (wavelength X/2) as emergent light I2.Then, can separate residual first-harmonic among the emergent light I2, only take out second harmonic by prism 65.Have, available separation vessel replaces prism 65 again.

According to present embodiment cause first crystal 63 and second crystal 64 that damaging and conversion efficiency has particular kind of relationship owing to adopted for fast light, can remedy the shortcoming of each crystal each other, realize on the whole high conversion efficiency with high fast light cause damaging.Therefore, can obtain high-power second harmonic expeditiously.

Have, present embodiment is in order to the generation second harmonic again, but the present invention can be widely used in and generation frequently.When for example producing third harmonic, in the laser oscillation system of the embodiment of Fig. 8, can adopt: replace separation vessel 61,62 with the catoptron that reflects each first-harmonic and second harmonic, and the structure of having removed light beam damper 66.Perhaps, also can adopt a separation vessel 61,62, light beam damper 66 all to remove,, first-harmonic and second harmonic are directly incident on the structure of first crystal 63 by the oscillator that produces first-harmonic and second harmonic simultaneously.

Embodiment

(embodiment 1)

In the laser oscillation system of Fig. 8, it is the LB4 of 5mm * 5mm, long 35mm that first crystal 63 adopts the cross section, and it is the BBO of 5mm * 5mm, long 7mm that second crystal 64 adopts the cross section.Then, be incident light I0 incident with the green laser of average power 30W, repetition frequency 10kHz, pulsewidth 30nsec, beam diameter 0.5mm, wavelength 532nm, produce second harmonic.

At this moment, the average peak power density of incident light I0 is 51MW/cm ², but the power of residual first-harmonic (532nm) is that 28.5W, average peak power density become 48.4MW/cm among the emergent light I1 ²And the stable ultraviolet light (266nm) that has obtained output power and be 6.3W is as emergent light I2.

In addition, be 48.4MW/cm with the average peak power density ²Ordinary beam of light (532nm) incident BBO the time, can produce body damage.But, under the situation of present embodiment, as shown in Figure 9,, do not damage so produce body because actual peak power density reduces.

(comparative example 1)

In the laser oscillation system of Fig. 8, it is the BBO of 5mm * 5mm, long 7mm that first crystal 63 and second crystal 64 all adopt the cross section.The condition of incident light I0 is identical with embodiment 1.

At this moment, BBO can not use because of incident light I0 is subjected to the body damage.

(embodiment 2)

In the laser oscillation system of Fig. 8, it is the LB4 of 5mm * 5mm, long 35mm that first crystal 63 adopts the cross section, and it is the CLBO of 5mm * 5mm, long 10mm that second crystal 64 adopts the cross section.Then, be incident light I0 incident with green laser with average power 30W, the repetition frequency 10kHz of embodiment 1 the same terms, pulsewidth 30nsec, beam diameter 0.5mm, wavelength 532nm, produce second harmonic.

At this moment, the average peak power density of incident light IO is 51MW/cm ², but the power of residual first-harmonic (532nm) becomes 28.5W among the emergent light I1, the average peak power density becomes 48.4MW/cm ²And the stable ultraviolet light (266nm) that has obtained output power 6.5W is as emergent light I2.

Having, is 48.4MW/cm with the average peak power density again ²Ordinary beam of light (532nm) incident CLBO the time, can produce body damage.But, in the present embodiment, as shown in Figure 9, because peak power density has substantial reduction, so do not produce the body damage.

(comparative example 2)

In the laser oscillation system of Fig. 8, it is the CLBO of 5mm * 5mm, long 10mm that first crystal 63 and second crystal 64 all adopt the cross section.The condition of incident light I0 is identical with embodiment 1,2.

At this moment, CLBO can not use because of incident light I0 is subjected to the body damage.

(comparative example 3)

In the laser oscillation system of Fig. 8, it is the LB4 of 5mm * 5mm, long 35mm that first crystal 63 and second crystal 64 all adopt the cross section.The condition of incident light I0 is identical with embodiment 1,2.

At this moment, the average peak power density of incident light I0 is 51MW/cm ², but the power of residual first-harmonic (532nm) becomes 28.5W among the emergent light I1, and the average peak power density becomes 48.4MW/cm ²And the ultraviolet light (266nm) that has obtained output power and be 3W is as emergent light I2.

The output of this emergent light I2 is stable, also can not produce the body damage, but compare with the 6.3W of embodiment 1 or the 6.5W of embodiment 2, and its performance number is lower.

(embodiment 3)

The laser oscillation system of present embodiment produces and frequently, in its structure: replace the separation vessel 61,62 of laser oscillation system of the embodiment of Fig. 8 with the catoptron of reflection first-harmonic and second harmonic, and removed light beam damper 66.

In this laser oscillation system, it is the LB4 of 5mm * 5mm, long 35mm that first crystal 63 adopts the cross section, and it is the LBO of 5mm * 5mm, long 15mm that second crystal 64 adopts the cross section.Then, be incident light I0 incident with the fundamental wave of laser of wavelength 1064nm, average power 10W and the second harmonic of wavelength 532nm, average power 10W, producing third harmonic is the Ultra-Violet Laser of wavelength 355nm.

Among this incident light I0, repetition frequency is 10kHz, and the pulsewidth of fundamental wave of laser, second harmonic laser and beam diameter are respectively 30nsec, 0.3mm, 27nsec, 0.2mm.

At this moment, the average peak power density of the fundamental wave of laser of incident light I0, second harmonic laser is respectively 47MW/cm ², 118MW/cm ², but residual first-harmonic and the power of second harmonic are respectively 9.5W, 9.5W among the emergent light I1, and the average peak power density becomes 45MW/cm respectively ², 112MW/cm ²So the stable third harmonic (355nm) that has obtained output power and be 5W is as emergent light I2.

Having, is 112MW/cm with the average peak power density again ²Ordinary beam of light (532nm) incident LBO the time, can produce body damage.But, under the situation of present embodiment, as shown in Figure 9,, do not damage so produce body because actual peak power density reduces.

(comparative example 4)

In the laser oscillation system identical with embodiment 3, it is the LBO of 5mn * 5mm, long 10mm that first crystal 63 and second crystal 64 all adopt the cross section.The condition of incident light I0 is identical with embodiment 3.

In this case, because LBO can be subjected to the body damage at leisure because of the second harmonic among the incident light I0 (532nm), be restricted and can not stably use for a long time service time.

(comparative example 5)

In the laser oscillation system identical with embodiment 3, it is the LB4 of 5mm * 5mm, long 35nm that first crystal 63 and second crystal 64 all adopt the cross section.The condition of incident light I0 is identical with embodiment 3.

In this case, having obtained output power is that the stable third harmonic (355nm) of 2W is as emergent light I2.

The output of this emergent light I2 is stable, also can not produce the body damage, but compare with the 5W of embodiment 3, and its performance number is lower.

(embodiment 4)

The laser oscillation system of present embodiment produces and frequently, in its structure: replace the separation vessel 61,62 of laser oscillation system of the embodiment of Fig. 8 with the catoptron of reflection first fundamental wave and second fundamental wave, and removed light beam damper 66.

In this laser oscillation system, it is the LB4 of 5mm * 5mm, long 20mm that first crystal 63 adopts the cross section, and it is the BBO of 5mm * 5mm, long 15mm that second crystal 64 adopts the cross section.Then, with the third harmonic (first fundamental wave) of the Nd:YAG laser of wavelength 355nm, average power 5W and the Ti of wavelength 828nm, average power 5W: sapphire laser (second fundamental wave) is incident light I0 incident, produces and is the Ultra-Violet Laser of wavelength 248nm frequently.

In this incident light I0, repetition frequency is 10kHz, and the pulsewidth and the beam diameter of first fundamental wave (355nm), second fundamental wave (828nm) are respectively 25nsec, 0.2mm, 15nsec, 0.2mm.

At this moment, the average peak power density of the first fundamental wave of incident light I0 (355nm), second fundamental wave (828nm) is respectively 64MW/cm ², 106MW/cm ², but residual first fundamental wave (355nm) and the power of second fundamental wave (828nm) are respectively 4.85W, 4.85W among the emergent light I1, and the average peak power density becomes 62MW/cm respectively ², 103MW/cm ²So, obtained the stable of output power 0.8W and frequently (248nm) as emergent light I2.

In addition, be 62MW/cm with the average peak power density ²Ordinary beam of light (355nm) when inciding BBO, can produce the body damage.But, under the situation of present embodiment, as shown in Figure 9,, do not damage so produce body because actual peak power density reduces.

(comparative example 6)

In the laser oscillation system identical with embodiment 4, it is the BBO of 5mm * 5mm, long 15mm that first crystal 63 and second crystal 64 all adopt the cross section.The condition of incident light I0 is identical with embodiment 4.

In this case, because of the effect of the first fundamental wave among the incident light I0 (355nm), BBO is subjected to the body damage at leisure, and therefore, be restricted its service time, can not stably use for a long time.

(comparative example 7)

In the laser oscillation system identical with embodiment 4, it is the LB4 of 5mm * 5mm, long 20mm that first crystal 63 and second crystal 64 all adopt the cross section.The condition of incident light I0 is identical with embodiment 4.

In this case, obtained output power be the stable of 0.4W and frequently (248nm) as emergent light I2.

The output of this emergent light I2 is stable, also can not produce the body damage, but compare with the 0.8W of embodiment 4, and its performance number is lower.

The industrial possibility of utilizing

As mentioned above, according to Wavelength conversion method of the present invention and wavelength conversion system, Below the good peak power density, because close near the peak power the optimum peak power density The incident light of degree carries out wavelength conversion, can particularly use Jiao with the nonlinear optical crystal monocrystal Lithium borate LB4 reaches stable high conversion efficiency. Therefore, according to the present invention, can realize Durable total solids Ultra-Violet Laser oscillator.

And, adopt program of the present invention and medium, owing to can easily try to achieve best peak The value power density, the operator advances under the condition of predetermined repetition frequency, predetermined crystal length Row is to the emergent light that obtains wavelength 1/2 λ behind the incident light of nonlinear optical crystal incident wavelength λ During the operation of wavelength conversion system, can set suitable peak power density.

And, according to Wavelength conversion method of the present invention and wavelength conversion system, because can Optimum peak power density is risen, also can obtain even improve the peak power density of incident light Power output that must be stable. Therefore, can enough monocrystalline lithium pyroborate LB4 etc. non-linear optical crystal Body is reached stable high conversion efficiency, can realize durable total solids Ultra-Violet Laser oscillator.

And, according to the present invention, have the different types of non-line of particular kind of relationship by combination The property optical crystal, can remedy shortcoming each other, realize that whole high conversion efficiency is with high anti-Photic damaging. Therefore, can obtain expeditiously high-power second harmonic etc. and frequently.

Claims (8)

1. optical wavelength conversion method, this method incides first nonlinear optical crystal with the first-harmonic of predetermined wavelength and time pulsewidth, to incide second nonlinear optical crystal again from the light of the described first nonlinear optical crystal outgoing then, produce the second harmonic of described first-harmonic, it is characterized in that:

Described first nonlinear optical crystal corresponding to the body damage threshold of described first-harmonic body damage threshold greater than described second nonlinear optical crystal, and

Effective nonlinear constant that the second harmonic for described first-harmonic of described second nonlinear optical crystal takes place is greater than effective nonlinear constant of described first nonlinear optical crystal.

2. optical wavelength conversion method, this method incides first nonlinear optical crystal with the first fundamental wave of predetermined wavelength and time pulsewidth and the second fundamental wave of predetermined wavelength and time pulsewidth, to incide second nonlinear optical crystal again from the light of the described first nonlinear optical crystal outgoing then, produce described first fundamental wave and second fundamental wave and frequently, it is characterized in that:

Described first nonlinear optical crystal corresponding to the body damage threshold of described first fundamental wave body damage threshold greater than described second nonlinear optical crystal, and

Described second nonlinear optical crystal for from described first fundamental wave and second fundamental wave and the effective nonlinear constant of living effective nonlinear constant that take place frequently greater than described first nonlinear optical crystal.

3. as claim 1 or the described optical wavelength conversion method of claim 2, it is characterized in that:

Described first nonlinear optical crystal is the monocrystalline lithium pyroborate.

4. optical wavelength conversion method as claimed in claim 3 is characterized in that:

Described second nonlinear optical crystal is LiB ₃O ₅, CsLiB ₆O ₁₀, KTiOPO ₄Or β-BaB ₂O ₄

5. optical wavelength conversion system, this system is provided with first nonlinear optical crystal that produces second harmonic because of the first-harmonic incident of predetermined wavelength and time pulsewidth, and, it is characterized in that because of the emergent light incident from this first nonlinear optical crystal produces second nonlinear optical crystal of the second harmonic of described first-harmonic:

Described first nonlinear optical crystal corresponding to the body damage threshold of described first-harmonic body damage threshold greater than described second nonlinear optical crystal, and

Effective nonlinear constant that the second harmonic for described first-harmonic of described second nonlinear optical crystal takes place is greater than effective nonlinear constant of described first nonlinear optical crystal.

6. optical wavelength conversion system, this system be provided with that second fundamental wave incident because of the first fundamental wave of predetermined wavelength and time pulsewidth and predetermined wavelength and time pulsewidth produces described first fundamental wave and second fundamental wave with first nonlinear optical crystal frequently, and, it is characterized in that because of the emergent light incident from this first nonlinear optical crystal produces described and second nonlinear optical crystal frequently:

Described first nonlinear optical crystal corresponding to the body damage threshold of described first fundamental wave body damage threshold greater than described second nonlinear optical crystal, and

Described second nonlinear optical crystal for from described first fundamental wave and second fundamental wave and the effective nonlinear constant of living effective nonlinear constant that take place frequently greater than described first nonlinear optical crystal.

7. laser oscillation system, this system be provided with the fundamental wave oscillator of the first-harmonic starting of oscillation of predetermined wavelength and time pulsewidth and by incident from the described first-harmonic of this fundamental wave oscillator and produce the optical wavelength conversion system of second harmonic, it is characterized in that:

Described optical wavelength conversion system is the described optical wavelength conversion system of claim 5.

8. laser oscillation system, this system is provided with the fundamental wave oscillator with the second fundamental wave starting of oscillation of the first fundamental wave of predetermined wavelength and time pulsewidth and predetermined wavelength and time pulsewidth, and produced and optical wavelength conversion system frequently from the described first fundamental wave of this fundamental wave oscillator and described second fundamental wave by incident, it is characterized in that:

Described optical wavelength conversion system is the described optical wavelength conversion system of claim 6.

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