CN1218448C - Biperiod superlattice and its application in laser frequency converter - Google Patents

Abstract

The present invention relates to a double-cycle superlattice and application thereof in laser frequency conversion. A ferroelectric crystal is used as a substrate by the kind of superlattice, and two reciprocal lattice vectors used for matching wave vector mismatch of frequency multiplication and frequency summing can be simultaneously provided by the arrangement of a specific double-modulation structure so that frequency tripling can be continuously increased. Thus, frequency tripling with high efficiency is realized, or the simultaneous output of frequency multiplication and frequency tripling is realized. A potassium tantalate (LiTaO3) superlattice with the kind of structure can be used for tripling frequency for 1064 nanometer lasers of an Nd: YVO4 laser device and an Nd: YAG laser device so as to output ultraviolet lasers of 355 nanometers.

Description

The superlattice of bi-period structure and the application in laser frequency thereof

Technical field

The present invention relates to a kind of superlattice setting of binary cycle modulated structure, and the application of this binary cycle superlattice in laser frequency, this superlattice have the function of direct frequency tripling.

Background technology

Wish that generation rather waits the people to deliver the article (S.N.Zhu of " realizing the green glow frequency tripling with Fibonacci optical superlattice paracycle (QPOS) " in 1997 on science, Yong-yuan Zhu, N.B.MingQuasi-Phase-Matched Third Harmonic Generation in a Quasi-Periodic OpticalSuperlattice Science 278,843 (1997)).Utilize the LiTaO of Fibonacci sequence paracycle _3-(lithium tantalate) superlattice, the Nd:YAG laser of frequency tripling 1570nm, the green glow of generation 523nm.The basic parameter 1=10.7 μ m of QPOS, A=24 μ m, B=17.5 μ m.The sample total length is 8mm, and thickness is 0.5mm.1570nm infrared light single produces green glow power and reaches 6mW by the QPOS frequency tripling, and conversion efficiency is 23%.

J.P.Meyn and M.M.Fejer have delivered " utilizing period polarized lithium tantalate to obtain ultraviolet output by two frequencys multiplication " (Meyn J.P on Opt.lett in 1997, Fejer MM Tunable ultraviolet-radiation by second-harmonic generation in periodically poled lithiumtantalate, PT LETT 22 (16): article 1214-1216 AUG 15 1997).Lithium tantalate (LiTaO _3-) or lithium niobate (LiNbO ₃) cycle of superlattice is 2.625 μ m, acquisition the wavelength of Ultra-Violet Laser be 325nm, its effective nonlinear coefficient is 2.6pm/V, is 55% of theoretical value.

People such as A.Arie have delivered article (the Arie A of " with period polarized KTP (titanium phosphate hydrogen potassium) accurate be complementary generation frequency multiplication green glow and ultraviolet light " on Optics Communications, Rosenman G, MahalV, et al.Green and ultraviolet quasi-phase-matched second harmonicgeneration in bulk periodically-poled KTiOPO4 OPT COMMUN 142 (4-6): 265-268OCT 15 1997), utilizing a block period is the frequency multiplication ultraviolet output to 783.5nm laser of the KTP superlattice realization of 8.98 μ m, the superlattice crystal of 1 centimeter length, when pump light is 259mW, can obtain the Ultra-Violet Laser of 75.3 μ W, conversion efficiency is 0.12%/W.

More than three pieces of articles introduced respectively with paracycle optical superlattice realize the green glow frequency tripling and with cycle optical superlattice realization laser ultraviolet frequency double.In first piece of article, use be superlattice paracycle of standard Fibonacci.Second piece of article and the 3rd piece of article are respectively with Periodic Superlattice 650nm and 783.5nm light source frequency multiplication to be realized Ultra-Violet Laser output.All such schemes all do not relate to double modulation structure superlattice and utilize the superlattice of this structure to realize laser frequency tripling, do not relate to 1064nm laser is carried out direct frequency tripling acquisition 355nm Ultra-Violet Laser.

Summary of the invention

The objective of the invention is to seek a kind of novel optical superlattice structure be set---double modulation structure, this structure can realize the multiwavelength laser frequency multiplication and to the laser frequency tripling of any wavelength.Thereby provide a kind of optical superlattice crystal as frequency tripling frequency inverted device, constitute and a kind ofly high efficiencyly small-sizedly all solid state can export green glow, blue light, purple light or near ultraviolet laser.Particularly adopt the LiTaO of a bi-period structure ₃Superlattice are to Nd:YVO ₁1064nm exports direct frequency tripling with the Nd:YAG laser, obtains the Ultra-Violet Laser output of 355 nanometers.

The present invention seeks to realize like this: the lithium tantalate LiTaO that utilizes a double modulation (binary cycle or cycle---paracycle) structure ₃, lithium niobate LiNbO ₃, potassium titanium oxide phosphate KTP superlattice are as the laser frequency medium, it is characterized in that: this double modulation structure can provide simultaneously be used for mating frequency multiplication and and two reciprocal lattice vectors of wave vector mismatch frequently, thereby the growth that frequency tripling can be continued realizes frequency tripling output efficiently.Since the position of the reciprocal lattice vector of this structure and big I by to structural parameters setting regulate, thereby can realize the especially efficient frequency tripling of laser of blue light, near ultraviolet and ultraviolet of any wave band.

Be the setting up procedure that example illustrates this double modulation structure superlattice now with the binary cycle superlattice:

Basic ideas are for fundamental wavelength arbitrarily, choose its periodic structure parameter make frequency multiplication process in the structure and and the wave vector mismatch equal and opposite in direction that produces of process frequently, in this case, second harmonic output is to wait amplitude or become the amplitude vibration.Triple-frequency harmonics output increases in slight vibration.The intensity of second harmonic triple-frequency harmonics is seen shown in Figure 3 with the relation of Periodic Superlattice crystal length, like this, be the new cycle primitive period structure to be modulated once more the cycle of oscillation of exporting with second harmonic.Consequently second harmonic obtains sustainable growth, causes triple-frequency harmonics light also can efficiently export.The intensity of first-harmonic, frequency multiplication and frequency tripling with the relation of binary cycle superlattice crystal as shown in Figure 4 (cycle---paracycle superlattice be provided with thought and method with).Fig. 1 and Fig. 2 are wherein a kind of template and frequency spectrums of the binary cycle plan of establishment.

We see in Fig. 1, and double-periodic major parameter is the cycle l of little periodic structure and big structure L modulation period.If these two parameters have determined that bi-period structure has just been determined basically.Below we look at how to derive this two basic parameters by the requirement that is provided with.

Fig. 2 is the typical frequency spectrum figure of bi-period structure.We use Gm, and n represents the main reciprocal lattice vector of this bi-period structure, and m, n are integers:

$\mathrm{Gm},n=\frac{2\mathrm{\πm}}{l}+\frac{2\mathrm{\πn}}{L}\·\·\·\·\·\·\left(1\right)$

Δ K ₁, Δ K ₂Represent respectively frequency multiplication and and the wave vector mismatch in the process frequently, if we select the Gm in the bi-period structure, n and Gm ', n ' compensate this two wave vector mismatches respectively, then have

$\mathrm{Gm},n-\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="K"\; filenames="C0011900600081.png,C0011900600082.png"\; state="\{\{state\}\}">K</figure-callout>}}_1=\frac{2\mathrm{\&pi;m}}{l}+\frac{2\mathrm{\&pi;n}}{L}-\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="K"\; filenames="C0011900600081.png,C0011900600082.png"\; state="\{\{state\}\}">K</figure-callout>}}_1=0$

$G{m}^{\&prime;},n^{\&prime;}-\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="C0011900600082.png,C0011900600101.png"\; state="\{\{state\}\}">K</figure-callout>}}_2=\frac{2{\mathrm{\&pi;m}}^{\&prime;}}{l}+\frac{2{\mathrm{\&pi;n}}^{\&prime;}}{L}-\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="C0011900600082.png,C0011900600101.png"\; state="\{\{state\}\}">K</figure-callout>}}_2=0\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\&CenterDot;\left(2\right)$

We can obtain the expression formula of double-periodic main structure parameters l and L by above formula:

$l=\frac{2\mathrm{\&pi;}({\mathrm{mn}}^{\&prime;}-m^{\&prime;}n)}{\mathrm{\&Delta;}{k}_1{n}^{\&prime;}-{\mathrm{\&Delta;k}}_{2}n}$

$L=\frac{2\mathrm{\&pi;}({\mathrm{nm}}^{\&prime;}-n^{\&prime;}m)}{\mathrm{\&Delta;}{k}_1{m}^{\&prime;}-{\mathrm{\&Delta;k}}_{2}m}$

................(3)

Δ k wherein ₁, Δ k ₂Can be expressed as again:

${\mathrm{\&Delta;<figure-callout\; id="1"\; label="k"\; filenames="C0011900600081.png,C0011900600082.png"\; state="\{\{state\}\}">k</figure-callout>}}_1=\frac{4\mathrm{\&pi;}}{\mathrm{\&lambda;}}(n_2-n_1)$

$\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="2"\; label="k"\; filenames="C0011900600082.png,C0011900600101.png"\; state="\{\{state\}\}">k</figure-callout>}}_2=\frac{2\mathrm{\&pi;}}{\mathrm{\&lambda;}}({3n}_3-{2n}_2-n_1)$

................(4)

(4) n in the formula ₁, n ₂, n ₃Be respectively the superlattice crystal at first-harmonic, two frequencys multiplication, the refractive index during frequency tripling.Generally speaking, select m=1, n=-1, m '=3, n '=1 (Fig. 1, Fig. 2 are exactly this situation).If the 1064nm with the most frequently used Nd laser is output as first-harmonic, it is 40 ℃ that temperature is set, two basic parameter l=6.77um of bi-period structure, and L=50.86um is (to LiTaO ₃).

In concrete the setting, one group be used for mating the frequency multiplication mismatch and and frequently two reciprocal lattice vectors of mismatch can do flexible selection.Can select G _{1 ,-1}, G _3,1Perhaps G _{1 ,-1}, G _{3 ,-1}Perhaps G _{1 ,-3}, G _{3 ,-1}, different selections causes different bi-period structures, corresponding to different fundamental wavelength.

Because ultraviolet, black light are near LiTaO ₃The ABSORPTION EDGE of crystal, the conversion efficiency of actual frequency tripling is more smaller than the Theoretical Calculation.Simultaneously, in order to eliminate the influence of photorefractive effect to conversion efficiency and optical quality, the coupling temperature of setting is preferably between 100 ℃～200 ℃.

The superlattice available iron electric crystal material of this bi-period structure is as LiTaO ₃, LiNbO ₃, KTP etc. prepare by room temperature polarization or striped growth method, also can be prepared into the double modulation domain structure fiber waveguide device with same frequency translation function in conjunction with waveguide technology.Be that LT, LN or KPT superlattice are as the laser frequency medium.

In material is provided with, need to utilize the dispersion equation of material refractive index, provide LiTaO here ₃The dispersion equation that contains temperature coefficient of monocrystalline:

${n_e}^2(\mathrm{\&lambda;},T)=A+\frac{B+b\left(T\right)}{{{\mathrm{\&lambda;}}^2-[C+c\left(T\right)]}^2}+\frac{E}{{\mathrm{\&lambda;}}^2-{\mathrm{<figure-callout\; id="2"\; label="F"\; filenames="C0011900600082.png,C0011900600101.png"\; state="\{\{state\}\}">F</figure-callout>}}^2}+{\mathrm{D\&lambda;}}^2$

Parameter wherein is:

A＝4.5284，B＝7.2449×10 ^-3，C＝0.2453，D＝-2.3670×10 ^-2，

E＝7.7690×10 ^-2，F＝0.1838，b(T)＝2.6794×10 ^-8(T+273.15) ²，

c(T)＝1.6234×10 ^-8(T+273.15) ².

To other materials such as LiNbO ₃, KTP etc. see also nonlinear optical material handbook and relevant document.

Characteristics of the present invention are: the present invention replaces the conventional nonlinear optical crystal that uses with the optical superlattice crystal, replaces cycle, quasi-periodic structure optical superlattice with double modulation structure optical superlattice, thereby can realize direct frequency tripling to any optical maser wavelength.Because LiTaO ₃Ultraviolet absorption edge adopts the LiTaO of a bi-period structure in 280 nanometers ₃Superlattice can be realized the direct frequency tripling to the most universal Nd laser 1064 nanometers output, obtain the ultraviolet output of 355 nanometers.Combine with semiconductor laser, can be developed into low threshold value, high efficiency, quality light beam, simple in structure and small-sized all-solid-state ultraviolet laser.Thereby in spectroscopy, biomedicine, biological medicine research, optical information stores and other fields must be used arriving widely.

Description of drawings:

Below in conjunction with accompanying drawing and specific embodiments the present invention is described in further detail:

Fig. 1 is the template schematic diagram of a kind of binary cycle plan of establishment of the present invention

Fig. 2 is the typical frequency spectrum figure of bi-period structure, and abscissa is a reciprocal lattice vector, and ordinate is the fourier coefficient value

Figure 3 shows that the graph of a relation of the intensity of second harmonic, triple-frequency harmonics with the Periodic Superlattice crystal length.Frequency tripling efficient is along with the length of crystal transverse axis increases and increases.Be the new cycle primitive period structure to be modulated once more the cycle of oscillation with second harmonic output.Consequently second harmonic obtains sustainable growth, causes triple-frequency harmonics light also can efficiently export.

Fig. 4 is the graph of a relation of the intensity of first-harmonic, frequency multiplication and frequency tripling with binary cycle superlattice crystal length, and wherein ordinate is represented conversion efficiency, and FG, SHG, three curves of THG are represented the conversion efficiency of first-harmonic, frequency multiplication and frequency tripling respectively, and abscissa is a length.

Fig. 5 is the structural representation of ultraviolet of the present invention, near ultraviolet laser.

Fig. 6 is the structural representation that a kind of plated film of ultraviolet of the present invention, near ultraviolet laser is provided with.

Fig. 7 is a kind of structural representation that adds the chamber setting of ultraviolet of the present invention, near ultraviolet laser.

Drawing is described as follows:

1-LD laser, wavelength are 808nm; The 2-focusing system is generally set of lenses;

3-Nd:YVO ₄Crystal, the laser medium of generation 1064nm laser;

4-Q-modulating device (as acousto-optic device); The outgoing mirror of 5-1064nm laser (as T=20%);

6-convergent lens (as f=50mm); The 7-temperature control furnace is used for regulating temperature;

8-binary cycle superlattice crystal produces the frequency multiplication green-yellow light, frequency tripling ultraviolet, near ultraviolet laser;

Ultraviolet, the near ultraviolet laser of 9-output, perhaps yellowish green, ultraviolet two-color laser;

The 10-multilayer film, the anti-reflection film of 1064nm, the high-reflecting film of 532nm;

The high-reflecting film of 11-532nm, the high transmittance film of 355nm;

The 12-resonator mirror is Multicolour mirror;

13-output chamber mirror, ultraviolet, near ultraviolet printing opacity

Embodiment:

Embodiment 1

Make frequency tripling near ultraviolet laser outside the chamber of forming with binary cycle superlattice according to Fig. 5.1 is the LD laser of 808 nanometers, and peak power output is 15W, Nd:YVO ₄The front surface plated film of crystal 3 and chamber mirror 5 constitute the resonant cavity of laser together, can produce the laser of quasi-continuous 1064 nanometers of about 2W behind chamber mirror 5.One block size cycle, (L, (be placed in the temperature control furnace (7), when regulating temperature control furnace to 45.4 degree centigrade, producing wavelength was the Ultra-Violet Laser (9) of 355 nanometers l) to be respectively the binary cycle lithium tantalate superlattice of 50.86 microns and 6.77 microns.The length that changes optical superlattice (8) can change the intensity of output Ultra-Violet Laser (9), and the length range of general superlattice arrives several centimetres at several millimeters.

Embodiment 2

Make a frequency tripling near ultraviolet laser of forming with binary cycle superlattice according to Fig. 6.Different with Fig. 5 plan of establishment is to carry out coating film treatment on former and later two surfaces of superlattice.Front surface plates the anti-reflection film of 1064 nanometers, the high-reflecting film of 532 nanometers; The high-reflecting film of 532 nanometers is plated in the rear surface, the high transmittance film of 355 nanometers.At the inner resonance of realizing frequency multiplication 532 nanometer lasers of superlattice, make it reach certain intensity like this, the transmitance of rear surface 532 nanometer high-reflecting films can be regulated the intensity of output green glow.Because the raising of double-frequency laser intensity in superlattice, the efficient of frequency tripling ultraviolet light will obviously improve, and the chamber mirror can realize exporting the different proportionings of green glow and ultraviolet light in the adjusting of different-waveband transmitance simultaneously.

Embodiment 3, make one according to Fig. 7 and add chamber frequency tripling near ultraviolet laser with what binary cycle superlattice were formed.With a block size cycle (L, l) the binary cycle lithium tantalate superlattice 8 that are respectively 50.86 microns and 6.77 microns are placed in the resonant cavity, speculum 12 is a Multicolour mirror, the frequency doubled light of the 532nm that is all-trans through the pump light of 1064nm, chamber mirror 13 sees through the ultraviolet light of 355nm, and can regulate as required the transmitance of 532nm.The same with embodiment 2, can realize the double-colored output of frequency multiplication green glow and frequency tripling ultraviolet simultaneously, the intensity between them also can be regulated in the transmitance of different-waveband by the chamber mirror, and beam quality has improvement greatly.

Claims (3)

1, the super crystal lattice material of bi-period structure is characterized in that with ferroelectric crystal material LiTaO ₃, LiNbO ₃, KTP is by room temperature polarization or the striped growth method prepares or become to have the material of following structural parameters in conjunction with the waveguide prepared, uses Gm, n represents the main reciprocal lattice vector of this bi-period structure, m, n are integers:

$\mathrm{Gm},n=\frac{2\mathrm{\&pi;m}}{l}+\frac{2\mathrm{\&pi;n}}{L}$

Δ K ₁, Δ K ₂Can represent again frequency multiplication and and the wave vector mismatch in the process frequently, select the super crystal lattice material Gm of bi-period structure, n and Gm ', n ' compensate this two wave vector mismatches respectively, then have

$\mathrm{Gm},n-\mathrm{\&Delta;}{K}_1=\frac{2\mathrm{\&pi;m}}{l}+\frac{2\mathrm{\&pi;n}}{L}-{\mathrm{\&Delta;K}}_1=0$

${\mathrm{Gm}}^{\&prime;},n^{\&prime;}-{\mathrm{\&Delta;K}}_2=\frac{2\mathrm{\&pi;m}}{l}+\frac{2\mathrm{\&pi;n}}{L}-{\mathrm{\&Delta;K}}_2=0$

By Gm, n and Gm ', n ' compensate this two wave vector mismatches respectively, thus the expression formula of 1 and L of double-periodic main structure parameter:

$l=\frac{2\mathrm{\&pi;}({\mathrm{mn}}^{\&prime;}-{\mathrm{nm}}^{\&prime;})}{{\mathrm{\&Delta;K}}_1{n}^{\&prime;}-{\mathrm{\&Delta;k}}_{2}n}$

$L=\frac{2\mathrm{\&pi;}(m^{\&prime;}n-n^{\&prime;}m)}{{\mathrm{\&Delta;K}}_1{m}^{\&prime;}-{\mathrm{\&Delta;k}}_{2}m}$

${\mathrm{\&Delta;k}}_1=\frac{4\mathrm{\&pi;}}{\mathrm{\&lambda;}}(n_2-n_1),{\mathrm{\&Delta;k}}_2=\frac{2\mathrm{\&pi;}}{\mathrm{\&lambda;}}({3n}_3-{2n}_2-n_1)$

N in the following formula ₁, n ₂, n ₃Be respectively the superlattice crystal at first-harmonic, two frequencys multiplication, the refractive index during frequency tripling.

2,, it is characterized in that one group is used for mating the frequency multiplication mismatch and does selection flexibly with two reciprocal lattice vectors of frequency mismatch, can select G by the super crystal lattice material of the described bi-period structure of claim 1 _{1 ,-1 '}G _3,1Perhaps G _{1 ,-1 '}G _{3 ,-1}Perhaps G _{1 ,-3 '}G _{3 ,-1 '}Obtain different bi-period structures, corresponding to different fundamental wavelength.

3, the application of binary cycle superlattice in laser frequency is characterized in that utilizing the LiNbO of a double modulation or bi-period structure ₃, the double-periodic main structure parameter of KTP the expression formula of 1 and L:

$l=\frac{2\mathrm{\&pi;}({\mathrm{mn}}^{\&prime;}-{\mathrm{nm}}^{\&prime;})}{{\mathrm{\&Delta;K}}_1{n}^{\&prime;}-{\mathrm{\&Delta;k}}_{2}n}$

$L=\frac{2\mathrm{\&pi;}(m^{\&prime;}n-n^{\&prime;}m)}{{\mathrm{\&Delta;K}}_1{m}^{\&prime;}-{\mathrm{\&Delta;k}}_{2}m}$

${\mathrm{\&Delta;k}}_1=\frac{4\mathrm{\&pi;}}{\mathrm{\&lambda;}}(n_2-n_1){,\mathrm{\&Delta;k}}_2=\frac{2\mathrm{\&pi;}}{\mathrm{\&lambda;}}(3n_3-2n_2-n_1)$

N in the following formula ₁, n ₂, n ₃Be respectively the superlattice crystal at first-harmonic, two frequencys multiplication, the refractive index during frequency tripling.

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