CN105375255A - Laser output power optimization method based on variable-transmittance endoscope - Google Patents

Abstract

The invention relates to a laser output power optimization method based on a variable-transmittance endoscope, and belongs to the technical field of laser. The method comprises the following specific steps: (1) calculating the output power of a needed pump source according to the requirement of the design index on the laser output characteristic; (2) calculating the optimal transmittance values under different pump power according to the range of pump power and the optimal transmittance formula; (3) determining the coating requirement of the variable-transmittance endoscope according to the tuning characteristics of the oscillation wavelength of a laser; (4) making the variable-transmittance endoscope according to the coating requirement; (5) adopting the selected pump source and the variable-transmittance endoscope to build a laser system; (6) setting the pump power, and adjusting a laser resonator to obtain laser output; (7) tuning the laser wavelength; and (8) making the laser work stably at the optimal transmittance to obtain the maximum output power, thus completing online optimization of the output power of the laser. According to the invention, there is no need to insert elements into the cavity, and the loss is low. The optimization method is simple, reliable in work, convenient in operation, and wide in adaptability.

Description

Based on the laser output power optimization method becoming transmitance chamber mirror

Technical field

The present invention relates to a kind of optimization method of laser output power, particularly a kind of laser output power optimization method based on becoming transmitance chamber mirror, belongs to laser technology field.

Background technology

Laser has that good directionality, coherence are high, power density high, is all widely used, can be applicable to the fields such as spectrum analysis, remote sensing, laser radar and infrared guidance in civilian and military field.For obtaining Low threshold, high efficiency Laser output, the optimal design of laserresonator is extremely important.According to the output principle of laser, for certain pump power and oscillation wavelength, there is a Best Coupling output rating (namely chamber mirror is to the transmitance of oscillation light), make power output reach maximum.

For the optimization of coupling output rate, method conventional is at present the actual measurement of theory calculate Binding experiment.Namely the scope of the optimum transmission of chamber mirror is first determined by theory calculate and engineering experience; Then in the scope determined, according to certain step-length, the chamber mirror that a series of transmitance is different is made; Finally adopt experimentally, determine the optimum value of chamber mirror transmitance by the size of laser output power during contrast employing different transmitance chamber mirror, realize the optimization to power output.This traditional optimization method is not only wasted time and energy, and considerably increases development cost; And the optimization that cannot simultaneously realize under different pumping condition, very inconvenient on engineer applied.

Summary of the invention

The object of the invention is the problem that cannot realize online optimization output power in order to solve usual laser for different operating power, a kind of laser output power optimization method based on becoming transmitance chamber mirror is provided.

The present invention, in conjunction with the tuning characteristic of laser output wavelength, adopts this method, can not change resonant cavity element and do not change cavity resonator structure condition under, realize the on-line optimization to laser output power under different operating state.Meanwhile, it also avoid the development cost caused because making multiple output coupling mirror to increase.

The object of the invention is to be achieved through the following technical solutions.

Based on the laser output power optimization method becoming transmitance chamber mirror, its step comprises:

Step one: according to design objective to the requirement of laser output characteristic, adopt corresponding principle formula, calculates the power output of required pumping source;

Step 2: according to the optimum transmission value under pump power scope and the different pump power of optimum transmission formulae discovery;

Step 3: determine the plated film requirement becoming transmitance chamber mirror according to the tuning characteristic of laser oscillation wavelength;

Step 4: according to plated film requirement, carries out change transmitance chamber mirror and makes;

Step 5: adopt selected pumping source and become transmitance chamber mirror and build Optical Maser System;

Step 6: setting pump power, regulates laserresonator to obtain Laser output;

Step 7: carry out tuning to optical maser wavelength, now the transmitance of laser is modulated.The power output of surveying work laser when different wave length, find out power output maximum time corresponding optical maser wavelength, transmitance corresponding to this wavelength i.e. optimum transmission of laser under pump power for this reason;

Step 8: make laser stabilization be operated in optimum transmission place, obtains maximum power output, namely achieves the on-line optimization of laser output power.

For different Optical Maser Systems in step one, its specific formula for calculation is different.Such as, for common continuous running, four-level laser, when chamber mirror transmitance is best, its power output can be expressed as:

$P_{out}=g_0{\mathrm{lI}}_{s}A{(1-\sqrt{\mathrm{\δ}/2g_{0}l})}^2---\left(1\right)$

G in formula ₀for the small signal gain of oscillation light, relevant with pump power:

g ₀＝στ _fη _Qη _SV _Bη _abP _pV/hv _L(2)

σ is that stimulated emission cross section amasss, relevant to the character of gain media and optical maser wavelength; τ _ffor the upper laser level life-span; η _qfor external quantum efficiency, represent effective stimulated emission population and the ratio being energized into upper laser level population; η _sfor the Stokes factor; Both products are:

η _Qη _S＝v _L/v _P(3)

ν _lfor laser frequency, ν _pfor pump light frequency.

η _bfor the conversion efficiency that the overlap factor of running laser mode and pump mode determines, Gaussian beam is had:

${\mathrm{\η}}_B=\frac{2w_L^2}{w_L^2+x_P^2}---\left(4\right)$

Wherein w _lfor girdling the waist of the light beam that vibrates in chamber, w _pfor girdling the waist of pump beam.

η _ababsorption efficiency for gain media: η _ab=1-exp (-α _abl), α _abfor gain media is to the absorption coefficient of pump light; L is gain media length.P _pfor pumping light power; V is gain medium volume; H is Planck's constant.A is that gain medium cross-section amasss; δ is total losses in the resonant cavity except the mirror of chamber; I _ssaturation gain for gain media:

I _s＝hv _L/στ _f(5)

From (1)-(5) formula, when after selected gain media resonant cavity basic parameter, the laser power exported as required, can calculate the pump power of required pumping source.

In step 2, given pump power, the optimum transmission of laserresonator can be calculated by following formula:

$-ln(1-T_{opt})=(\sqrt{\frac{2g_{0}l}{\mathrm{\δ}}}-1)/\mathrm{\δ}---\left(6\right)$

Wherein T _optfor the transmitance (i.e. Best Coupling output rating) of chamber mirror; g ₀calculate according to formula (2).P _pspan be pumping threshold to the pump power calculated according to step one, can T be obtained thus _optspan.

In step 5 when building Optical Maser System, designed resonant cavity need consider the thermal lensing effect of gain media, to ensure at whole pump power P _pall meet stable oscillation stationary vibration condition in span, and be in the position of stable region compared with center.

In step 7, the technological means such as tuning tuning by thermal tuning, Resonant Intake System, the seed injection wavelength tuning (when having seed laser and injecting) of optical maser wavelength are realized; Wavelength tuning should carry out in scope less around gain media laser center wavelength, little on power output impact to ensure the change in gain that wavelength tuning causes.

Compared with existing optimization method, the invention has the beneficial effects as follows:

1, under the condition not changing element and structure, the on-line optimization to resonant cavity power output under different pump power and different operating state can be realized.

2, wide accommodation, can be used for all various lasers had compared with wide spectral tuning range, realizes the optimization of its power output.

3, without the need to insertion element in chamber, loss is little; Optimization method is simple, reliable operation, easy to operate.

Accompanying drawing explanation

Fig. 1 is under certain pump power, different transmitance for ideler frequency optical output power;

When Fig. 2 is for getting optimum transmission, the input-output curve of laser system;

Fig. 3 is the optimum transmission in pumping source working range;

Fig. 4 is oscillator signal light and export the ideler frequency optical wavelength tuning curve with temperature in chamber;

Fig. 5 is the plated film requirement becoming transmitance chamber mirror;

Fig. 6 is the transmittance curve of change through chamber mirror of making;

Fig. 7 is that application the present invention is optimized involved laser structure schematic diagram;

Fig. 8 is the experimental result that application the present invention is optimized.

Embodiment

Below in conjunction with drawings and Examples, the present invention is further described.

Above-mentioned optimization method is applied to infrared continuous running optical parametric oscillator (OPO) in flashlight single resonance by the present embodiment.Mid-infrared light parametric oscillator involved by embodiment is based on the MgO:PPLN crystal of quasi-phase matched.This type of optical parametric oscillator has wider Spectral matching live width and has good temperature wavelength tuning characteristic, is therefore highly suitable for optimization method involved in the present invention.Concrete Optimization Steps is as follows:

Step one: design object is the 3.0 mu m waveband mid-infrared lasers outputs that generation power output is not less than 2W.According under quasi-phase matched condition, the conservation of momentum relation under the conservation of energy of three-wave interaction and collinear condition

Can obtain, when pumping wavelength is 1064nm, when working temperature is 25 DEG C, obtain 3.0 mu m waveband mid-infrared lasers and export, in OPO chamber, the wavelength of oscillator signal light is about 1.6 μm, and the polarization cycle of MgO:PPLN crystal is 30.5 μm.Wherein, λ _p, λ _sand λ _ibe respectively the wavelength of pump light, flashlight and ideler frequency light, n _p, n _sand n _ibe respectively the refractive index of pump light, flashlight and ideler frequency light, Λ is the polarization cycle of MgO:PPLN crystal.After each wavelength and corresponding refractive index are determined, according to flashlight single resonance three couple waves equation, when light distribution is basic mode Gaussian Profile, the formula of the operation threshold of OPO, gain and ideler frequency optical output power is:

$G\left(r\right)=g_0^2\left(r\right)l^2=\frac{2{\mathrm{\ω}}_s{\mathrm{\ω}}_i{d}_{eff}^2{l}^2}{n_p{n}_s{n}_i{c}^3{\mathrm{\ϵ}}_0}{I}_p\exp (-\frac{2r^2}{{\stackrel{\‾}{w}}_p^2})---\left(10\right)$

$P_i=\frac{{\mathrm{\ω}}_i}{{\mathrm{\ω}}_s+{\mathrm{\ω}}_i}\·{\∫}_0^{r_0}{\sin }^2\[g_0\left(r\right)l\]\·I_p\exp \left(-\frac{2r^2}{{\stackrel{\‾}{w}}_p^2}\right)\·2\mathrm{\π}rdr---\left(11\right)$

Wherein a _sfor flashlight is in the intracavity round trip loss of a week, T _sfor flashlight transmitance, ε ₀for dielectric constant in vacuum, c is the light velocity in vacuum, d _efffor effective nonlinear coefficient, for pump light is at intracrystalline average spot radius, h _smfor being mated the normalization decay factor introduced by Gaussian beam, I _pfor pump light is in intracrystalline light intensity, ω _sand ω _ibe respectively the circular frequency of flashlight and ideler frequency light, r ₀for the spot radius determined by threshold value.The relation between ideler frequency optical output power and flashlight transmitance under given pump power can be calculated thus.As shown in Figure 1, for certain pump power, the optimum value that there is transmitance makes ideler frequency optical output power the highest to result of calculation; When the optimum transmission value that different pump power is corresponding different.Mate completely in phase place, the transmitance of chamber mirror to oscillator signal light be when getting optimum value, the pump power obtained needed for 2W ideler frequency light output need be greater than 12W; As shown in Figure 2.Determine that pumping source peak power output is 20W thus.

Step 2: according to the determined pumping light power scope (0 ~ 20W) of step one, calculate optimum transmission as shown in Figure 3.When pump power increases, obtain most high conversion efficiency, the flashlight optimum transmission value of chamber mirror also increases; The excursion of transmitance is 0.1% ~ 2.2%.

Step 3: visible according to the tuning characteristic (Fig. 4) of optical parametric oscillator wavelength with temperature, when output ideler frequency optical wavelength is 3.1 μm ~ 3.2 μm (corresponding crystal temperature effect is 25 DEG C ~ 75 DEG C), when meeting design requirement, in chamber, oscillator signal optical wavelength is 1597nm ~ 1620nm.For realizing optimizing comparatively accurately, the transmitance becoming transmitance chamber mirror slowly should change in 1597nm ~ 1625nm wave-length coverage, and excursion is 0.1% ~ 2.2%.Consider theory error and coating process, become the coating designs curve of transmitance chamber mirror as shown in Figure 5; The transmitance becoming transmitance chamber mirror slowly should be changed to 4.5% by 0.1% in 1580nm ~ 1640nm wave-length coverage.

Step 4: the plated film according to calculating gained requires the transmitance of the change transmitance chamber mirror made as shown in Figure 6.Become the transmitance of transmitance chamber mirror in 1580nm ~ 1640nm wave-length coverage slowly to change, transmitance excursion is 0.2% ~ 5%; Meet better with design load.

Step 5: adopt infrared OPO in the system building shown in Fig. 7.Comprise pump laser (1), one-way isolator (2), coupling optical system (3), polarization beat length device (4), input mirror (5), nonlinear crystal (6) based on the OPO optimization output power device becoming transmitance chamber mirror, become transmitance chamber mirror (7) and high-precision temperature stove (8).Pump laser peak power output is 20W, centre wavelength 1064nm, and exporting light is line polarisation.Pump light converges to nonlinear crystal center by coupling optical system, and waist spot radius is about 100 μm.Isolated by one-way isolator between pump light and OPO resonant cavity.Nonlinear crystal is periodic polarized crystal MgO:PPLN, adopts the matching way of ee+e, to utilize the maximum non linear coefficient of periodic polarized crystal.Nonlinear crystal two optical surface is all coated with pump light, oscillator signal light and the counnter attack film exporting ideler frequency light three wave bands.Pump light is adjusted by half-wave plate in intracrystalline polarization state, and making it for the optical axis of crystal is e light.Input mirror forms optical resonator with change transmitance chamber mirror, makes flashlight single resonance.Nonlinear crystal is installed in temperature controlling stove, has fabulous thermal conductivity between the two, and isolates with surrounding environment heat.For obtaining 3.2 μm of ideler frequency light output, select the Crystal polarization cycle to be 30.5 μm, in corresponding cavity, oscillator signal optical wavelength is 1.6 μm.Input mirror is coated with pump light, oscillator signal light and the counnter attack film exporting ideler frequency light three wave bands towards the surface of coupled system, meanwhile, is coated with high thoroughly to pump light, anti-to flashlight height and to the counnter attack of ideler frequency light multilayer dielectric film towards the surface in chamber.Input mirror is coupled in chamber by low-loss for pump light, simultaneously as the high reflective mirror of flashlight; To the counnter attack of ideler frequency light to reduce to reflect the interference to resonant cavity.Become transmitance chamber mirror be coated with pump light towards the surface in chamber and ideler frequency light is high thoroughly, to flashlight transmitance with the gradual multilayer dielectric film of wavelength, and be coated with the counnter attack film to pump light, flashlight and ideler frequency light three wave bands towards the surface outside chamber.

Step 6: setting pump power is 16W, regulates resonant cavity to obtain mid-infrared laser and exports.Higher output is obtained by resonant cavity fine tuning.

Step 7: carry out tuning to oscillator signal optical wavelength by temperature controller, when crystal working temperature raises, signal light wavelength is elongated, and ideler frequency optical wavelength shortens.By to the control realization of temperature to the selection of transmitance.The power output of surveying work laser when different wave length as shown in Figure 8, when power output is maximum, temperature controlling stove temperature is 60 DEG C, and respective signal optical wavelength is 1612nm, the transmitance of corresponding change transmitance chamber mirror is 0.9%, is the Best Coupling output rating of OPO when pump power is 16W.

Step 8: make OPO steady operation at 60 DEG C of working points place, obtains the mid-infrared laser output that 2.5W wavelength is 3128nm.Achieve the on-line optimization of OPO power output.OPO output wavelength and power output all meet designing requirement.

The optimum transmission of testing acquisition in embodiment is smaller compared with theory calculate, its main cause is the pump light loss that the optical element such as pump coupling optical system, half-wave plate, chamber mirror is introduced to make the pump power of actual arrival nonlinear crystal be less than the power output of pumping source.When pump power reduces, corresponding Best Coupling transmitance value will diminish.

As can be seen here, by the optimisation technique of this invention, the on-line optimization to OPO power output infrared in flashlight single resonance can be realized.

Claims (5)

1., based on the laser output power optimization method becoming transmitance chamber mirror, it is characterized in that: comprise the steps:

Step one: according to design objective to the requirement of laser output characteristic, adopt corresponding principle formula, calculates the power output of required pumping source;

Step 2: according to the optimum transmission value under pump power scope and the different pump power of optimum transmission formulae discovery;

Step 3: determine the plated film requirement becoming transmitance chamber mirror according to the tuning characteristic of laser oscillation wavelength;

Step 4: according to plated film requirement, carries out change transmitance chamber mirror and makes;

Step 5: adopt selected pumping source and become transmitance chamber mirror and build Optical Maser System;

Step 6: setting pump power, regulates laserresonator to obtain Laser output;

Step 7: carry out tuning to optical maser wavelength, now the transmitance of laser is modulated; The power output of surveying work laser when different wave length, find out power output maximum time corresponding optical maser wavelength, transmitance corresponding to this wavelength i.e. optimum transmission of laser under pump power for this reason;

Step 8: make laser stabilization be operated in optimum transmission place, obtains maximum power output, namely achieves the on-line optimization of laser output power.

2. the laser output power optimization method based on becoming transmitance chamber mirror according to claim 1, is characterized in that: for different Optical Maser Systems in step one, and its specific formula for calculation is different.

3. the laser output power optimization method based on becoming transmitance chamber mirror according to claim 1, it is characterized in that: in step 2, given pump power, the optimum transmission of laserresonator can be calculated by following formula:

Wherein T _optfor the transmitance of chamber mirror, i.e. Best Coupling output rating; g ₀calculate according to formula (2); P _pspan be pumping threshold to the pump power calculated according to step one, can T be obtained thus _optspan.

4. the laser output power optimization method based on becoming transmitance chamber mirror according to claim 1, it is characterized in that: in step 5 when building Optical Maser System, designed resonant cavity need consider the thermal lensing effect of gain media, to ensure at whole pump power P _pall meet stable oscillation stationary vibration condition in span, and be in the position of stable region compared with center.

5. the laser output power optimization method based on becoming transmitance chamber mirror according to claim 1, is characterized in that: during tuning tuning by thermal tuning, Resonant Intake System, seed injection wavelength tuning to optical maser wavelength in step 7, technological means realizes; Wavelength tuning should carry out in scope less around gain media laser center wavelength, little on power output impact to ensure the change in gain that wavelength tuning causes.