CN100570461C - Chirped stretched laser pulse spectrum shaping device and method - Google Patents

Abstract

A spectrum shaping device and method for chirped stretched laser pulses, the device is composed of a mode-locked laser, a grating stretcher, a lens, a pulse sampler, an optical fiber beam splitter, an optical fiber amplifier, a synchronous photoelectric conversion device, a shaping electric pulse generator and an integrated waveguide electro-optical modulator. The invention can realize spectrum pre-shaping of chirped stretched pulses before amplification, greatly reducing the gain narrowing effect in the chirped pulse amplification system. The device does not require complex optical paths and mechanical devices, is very convenient to change the spectrum shape, is flexible to operate, has high efficiency, and is easily embedded in a chirped pulse multi-stage amplification system.

Description

Chirped stretched laser pulse spectrum shaping device and method

technical field

The invention relates to a chirped laser pulse, in particular to a chirped and stretched laser pulse spectrum shaping device and method thereof.

technical background

Chirped pulse amplification technology is often used in experimental devices for generating ultra-short and ultra-intense laser pulses of terawatts or even petawatts. The seed laser pulses are time-stretched in a stretcher, and then multi-stage amplified. Because the power density of the broadened seed laser pulse is too low, the amplification stage is usually divided into two stages: high-gain pre-amplification and power amplification. In the high-gain pre-amplification stage, the amplified laser pulse spectrum is usually narrowed due to the gain-narrowing effect of the laser medium, so that the final amplified laser pulse cannot be compressed back to the original pulse width. The application of spectral pre-shaping technology can reduce the spectral narrowing effect, so as to achieve laser pulse output with narrower pulse width and higher peak power density. In order to overcome the gain narrowing effect in the process of ultrashort laser pulse amplification, several spectral shaping methods have been proposed, such as loading narrow-band interference filters and quartz birefringent filters in the optical path, and using reflective variable pitch gratings. The method of realizing laser spectrum shaping, these methods meet the needs of the experiment to a certain extent, but there are still some problems, such as some sharp peaks in the shaped spectrum, it is cumbersome to change the shape of the spectrum, and the requirements for optical path adjustment accuracy are relatively high, stability Not good, device processing is more difficult and so on.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art, and provide a chirp-broadened laser pulse spectrum shaping device and method thereof. The shaping device and method do not need complex optical paths and mechanical devices, are very convenient to change the spectral shape, have flexible operation, high efficiency, and are easy to be embedded in a chirped pulse multi-stage amplification system.

The basic principle of the present invention is as follows:

The seed laser pulse is broadened by the grating, coupled into the single-mode fiber, and the laser single pulse is selected by the integrated waveguide modulator loaded with the gate electric pulse, and then time-shaped by the integrated waveguide modulator loaded with the shaping electric pulse, so as to realize spectral shaping .

The electric field intensity of the seed laser pulse is set as:

${\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; seeds</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; ]</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

After being widened by the stretcher:

${\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; str</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{<span\; class="notranslate">\; -</span><span\; class="notranslate">\; \&infin;</span>}{\overset{<span\; class="notranslate">\; \&infin;</span>}{<span\; class="notranslate">\; \&Integral;</span>}}{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; seeds</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; i\&phi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; i\&omega;t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; d\&omega;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

In the formula: $\mathrm{\&phi;}\left(\mathrm{\&omega;}\right)=\mathrm{\&phi;}\left({\mathrm{\&omega;}}_0\right)+{\mathrm{\&phi;}}^{\&prime;}\left({\mathrm{\&omega;}}_0\right)(\mathrm{\&omega;}-{\mathrm{\&omega;}}_0)+\frac{1}{2}{\mathrm{\&phi;}}^{\&prime;\&prime;}\left({\mathrm{\&omega;}}_0\right){(\mathrm{\&omega;}-{\mathrm{\&omega;}}_0)}^2,$ φ′, φ″ are group delay and group velocity dispersion coefficients respectively.

Time shaping in an integrated waveguide modulator:

ε(t) is the distribution function of the laser pulse electric field intensity with time after shaping. In the formula

In the formula: V _π , V _π/2 are the half-wave voltage and quarter voltage of the electro-optic modulation crystal, V(t) is the shaping electric pulse voltage, and V _dc is the DC bias voltage.

The distribution of the electric field intensity in the frequency domain can be obtained by performing Fourier transform on (3):

$\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{<span\; class="notranslate">\; -</span><span\; class="notranslate">\; \&infin;</span>}{\overset{<span\; class="notranslate">\; \&infin;</span>}{<span\; class="notranslate">\; \&Integral;</span>}}\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; i\&omega;t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; dt</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

So the spectral shape of the shaped laser pulse is:

I(ω)∝|ε(ω)| ² (6)

Technical solution of the present invention is as follows:

A spectral shaping device for chirped and stretched laser pulses, characterized in that the device consists of a mode-locked laser, a grating stretcher, a lens, a pulse sampler, an optical fiber beam splitter, an optical fiber amplifier, a synchronous photoelectric conversion device, and a shaped electric pulse generator It consists of an integrated waveguide optical modulator and an integrated waveguide optical modulator, and its positional relationship is: the ultrashort laser pulse to be shaped outputted by the mode-locked laser is stretched by a grating stretcher, and then coupled to the input end of the first single-mode optical fiber through a lens. The output end of the single-mode optical fiber is connected to the input end of the pulse sampler, and the output end of the pulse sampler is connected to the described optical fiber splitter through the second single-mode optical fiber, and the first output end of the optical fiber splitter is connected to The input end of the optical fiber amplifier, the output end of the optical fiber amplifier is connected to the described synchronous photoelectric conversion device through the fifth single-mode optical fiber, and the output end of the synchronous photoelectric conversion device is connected to the described shaping circuit through the first coaxial cable The input end of the pulse generator, the output end of the shaping electrical pulse generator is connected to the first input end of the integrated waveguide optical modulator through the second coaxial cable; the second output end of the optical fiber beam splitter is connected through the third unit The mode fiber is connected to the second input end of the integrated waveguide optical modulator, and the ultrashort laser pulse to be shaped is output from the fourth single-mode fiber after being modulated by a shaping electric pulse, and the spectrum is shaped.

The method for performing laser pulse spectrum shaping by the above-mentioned chirped stretched laser pulse spectrum shaping device comprises the following steps:

① The grating stretcher chirps and stretches the ultrashort seed laser pulses close to the Fourier transform limit, so that the frequency interval and time interval of the laser pulses are in a linear correspondence;

②The pulse sampler selects a single pulse for the high repetition frequency laser pulse sequence, so that the repetition frequency of the stretched laser pulse is reduced to 1Hz;

③A fiber beam splitter is used for laser pulse splitting, a synchronous trigger electrical pulse is generated through a synchronous photoelectric conversion device, and the shaping electrical pulse generator is driven to generate a shaping electrical pulse, so that it is highly synchronized with the laser pulse to be shaped;

④ Input the shaped electrical pulse generated by the shaped electrical pulse generator into the integrated waveguide optical modulator, and input the integrated waveguide optical modulator from the second output end of the optical fiber beam splitter through the third single-mode optical fiber The ultrashort laser pulse to be shaped at the second input end is subjected to electrical pulse shaping modulation, and is output through the fourth single-mode optical fiber.

Technical effect of the present invention:

1. The spectral shaping scheme can obtain a smooth and non-modulated shaped spectral waveform.

2. The spectrum shaping scheme has no complicated optical path, and the laser pulse is mainly transmitted in the optical fiber, which is easy to adjust and has high stability.

3. The spectrum shaping scheme can change the spectrum waveform very conveniently, only need to change the shaping electrical pulse waveform.

4. In this spectrum shaping scheme, the laser pulse is broadened and a single pulse is selected, so it can be easily embedded into the chirped laser pulse amplification system.

Description of drawings

Fig. 1 is a schematic structural diagram of a chirped stretched laser pulse spectrum shaping device of the present invention.

Figure 2 shows three shaped electrical pulse waveforms with different modulation depths.

Fig. 3 shows the shape of the laser pulse spectrum modulated by three different modulation depth shaping electric pulses corresponding to Fig. 2 .

Detailed ways

The present invention will be further described below in conjunction with the embodiments and accompanying drawings, but the protection scope of the present invention should not be limited thereby.

Please refer to FIG. 1 first. FIG. 1 is a schematic structural diagram of a chirped stretched laser pulse spectrum shaping device of the present invention. As can be seen from the figure, the spectrum shaping device for chirped and stretched laser pulses of the present invention consists of a mode-locked laser 1, a grating stretcher 2, a lens 3, a pulse sampler 5, an optical fiber beam splitter 6, an optical fiber amplifier 7, and a synchronous photoelectric conversion device 8 , a shaping electric pulse generator 10 and an integrated waveguide light modulator 11, and its positional relationship is: the ultrashort laser pulse output by the mode-locked laser 1 is stretched by the grating stretcher 2, and then coupled to the first laser pulse by the lens 3 The input end of the single-mode fiber 41, the output end of the first single-mode fiber 41 is connected to the input end of the pulse sampler 5, and the output end of the pulse sampler 5 is connected to the optical fiber splitter by the second single-mode fiber 42 6. The first output terminal of the optical fiber splitter 6 is connected to the input terminal of the optical fiber amplifier 7, and the output terminal of the optical fiber amplifier 7 is connected to the synchronous photoelectric conversion device 8 through the fifth single-mode optical fiber 45. The synchronous The output end of the photoelectric conversion device 8 is connected to the input end of the shaping electric pulse generator 10 through the first coaxial cable 91, and the output end of the shaping electric pulse generator 10 is connected to the integrated waveguide through the second coaxial cable 92 The first input end of the electro-optic modulator 11; the second output end of the optical fiber beam splitter 6 is connected to the second input end of the integrated waveguide optical modulator 11 through the third single-mode optical fiber 43, and the ultrashort laser to be shaped The pulse here is modulated by a shaped electric pulse, and then output by the fourth single-mode optical fiber 44, and the spectrum is shaped.

The process of performing laser pulse spectrum shaping by the chirped stretched laser pulse spectrum shaping device includes the following steps:

① The grating stretcher 2 chirps and stretches the ultrashort seed laser pulses input by the mode-locked laser 1 close to the Fourier transform limit, so that the frequency interval and time interval of the laser pulses are in a linear correspondence;

② The pulse sampler 5 selects a single pulse for the input chirped and broadened high repetition rate laser pulse sequence, so that the repetition frequency of the stretched laser pulse is reduced to 1 Hz;

③The optical fiber beam splitter 6 performs laser pulse splitting, and the weaker light beam generates a synchronous trigger electric pulse through the synchronous photoelectric conversion device 8, and promotes the shaping electric pulse generator 10 to generate a shaping electric pulse, so that it is compatible with the laser to be shaped The pulses are highly synchronized;

④ Apply the shaping electrical pulse generated by the shaping electrical pulse generator 10 to the integrated waveguide optical modulator 11, and input the integrated waveguide light modulator 11 through the third single-mode optical fiber 43 from the second output end of the optical fiber beam splitter 6. The ultrashort laser pulse to be shaped at the second input end of the waveguide optical modulator 11 undergoes electric pulse shaping modulation, and is output through the fourth single-mode optical fiber 44 .

In order to facilitate the understanding of the spectral shaping scheme proposed by the present invention, the following examples are used to describe the scheme, and numerically calculate the shaping electrical pulse waveform and the spectral waveform before and after shaping:

① The mode-locked laser 1 outputs a seed laser pulse of 220 fs, and the full width at half maximum of the spectrum is 7.4 nm.

② After the grating stretcher 2, the seed laser pulse is linearly stretched to 1.2ns.

③ Coupled into the single-mode fiber through the lens 3.

④ The sampler 5 is composed of an integrated waveguide modulator and a 1Hz square wave pulse generator. A single pulse is selected, and the laser pulse frequency is reduced to 1Hz.

5. the laser pulse is imported into the optical fiber beam splitter 6 through a single-mode optical fiber, and the laser pulse is divided into two bundles, and the weaker bundle is amplified through the optical fiber amplifier 7, and then the synchronous photoelectric conversion device 8 generates a synchronous trigger electric pulse. The pulses detrigger the shaped electrical pulse generator 10 to generate shaped electrical pulses.

6. A stronger beam of laser pulse output by the optical fiber beam splitter 6 is delayed through the third single-mode optical fiber 43, and is introduced into the integrated waveguide optical modulator 11 simultaneously with the shaping electric pulse, and the laser pulse is electro-optic modulated, and the time Due to the linear correspondence between the linear chirped laser pulse frequency interval and the time interval, the spectral waveform and time waveform of the shaped laser pulse are the same.

The voltage waveform of the shaped electric pulse is distributed with time as shown in FIG. 2 . Figure 3 is the corresponding spectrum shape, the solid line corresponds to the spectrum when the laser pulse is not shaped. After the spectrum of the laser pulse in Figure 3 has been shaped, the test shows that not only the waveform changes from a Gaussian shape to a flat-topped super-Gaussian shape, but even a depression can appear in the middle, and the half-maximum full width of the spectrum is 1-4nm wider than before shaping. .

Claims (2)

1, a kind of light spectrum shaping device of chirp spread laser pulse, it is characterized in that: this device is by mode-locked laser (1), grating stretching device (2), lens (3), pulse sample (5), fiber optic splitter (6), fiber amplifier (7), synchronizable optical electrical switching device (8), shaping electric pulse generator (10) and integrated waveguide electrooptic modulator (11) constitute, its position relation is: the ultrashort laser pulse of mode-locked laser (1) output, through grating stretching device (2) broadening, be coupled to the input end of first single-mode fiber (41) through lens (3) again, the input end of the output termination pulse sample (5) of this first single-mode fiber (41), the output terminal of this pulse sample (5) connects described fiber optic splitter (6) by second single-mode fiber (42), the input end of the first output described fiber amplifier of termination (7) of this fiber optic splitter (6), the output terminal of this fiber amplifier (7) connects described synchronizable optical electrical switching device (8) through the 5th single-mode fiber (45), the output terminal of this synchronizable optical electrical switching device (8) connects described shaping electric pulse generator (10) input end by first concentric cable (91), and the output terminal of this shaping electric pulse generator (10) connects described integrated waveguide electrooptic modulator (11) first input end by second concentric cable (92); Described fiber optic splitter (6) second output terminals connect second input end of described integrated waveguide electrooptic modulator (11) through the 3rd single-mode fiber (43), the ultrashort laser pulse process shaping electric pulse modulation back for the treatment of shaping is by the 4th single-mode fiber (44) output, and spectrum has obtained shaping.

2, the described chirp spread laser pulse light spectrum shaping device of claim 1 carries out the method for laser pulse light spectrum shaping, it is characterized in that comprising the following steps:

1. grating stretching device (2) carries out chirp spread to the ultrashort seed laser pulse near the Fourier transform limit of mode-locked laser (1) input, makes the frequency interval and the linear corresponding relation of the time interval of laser pulse;

2. pulse sample (5) is chosen monopulse to the high repetition frequency laser pulse sequence of chirp spread, makes the repetition frequency of the laser pulse behind the broadening be reduced to 1Hz;

3. use fiber optic splitter (6) and carry out the laser pulse beam splitting, more weak beam of laser promotes shaping electric pulse generator (10) by synchronizable optical electrical switching device (8) and produces the shaping electric pulse, makes it and treat shaped laser pulses maintenance high level of synchronization;

4. use the shaping electric pulse of shaping electric pulse generator (10) generation and import described integrated waveguide electrooptic modulator (11), to carrying out electric pulse shaping modulation through the ultrashort laser pulse for the treatment of shaping of second input end of the 3rd single-mode fiber (43) the described integrated waveguide electrooptic modulator of input (11), export by the 4th single-mode fiber (44) by described fiber optic splitter (6) second output terminals.

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