CN201054063Y - Optical Parametric Chirped Pulse Amplification Laser System - Google Patents

Abstract

An optical parametric chirped pulse amplification laser system includes a titanium sapphire femtosecond mode-locked pulse oscillator, a first beam splitter, a CEP stable signal pulse source, an OPCPA synchronous pump source, an OPCPA amplifier stage and a compressor. In the output beam direction of the titanium sapphire femtosecond mode-locked pulse oscillator is the first beam splitter, which splits the laser beam into a transmission beam and a reflection beam. In the transmission beam direction are the CEP stable signal pulse source, the OPCPA amplifier stage and the compressor in sequence. The CEP stable signal pulse source is composed of a photonic crystal fiber, a chirped mirror, a periodically polarized lithium niobate crystal and a stretcher; the OPCPA amplifier stage is composed of a first dichroic mirror, a first nonlinear crystal, a second dichroic mirror and a second nonlinear crystal; the OPCPA synchronous pump source is composed of a Q-switched frequency-doubled YAG laser, a narrow-band titanium sapphire regenerative amplifier, a second beam splitter and a total reflector. The utility model device can obtain near-infrared ultrashort laser pulse output with a pulse width of less than 30 femtoseconds.

Description

Optical Parametric Chirped Pulse Amplification Laser System

technical field

The utility model relates to a laser system, in particular to a near-infrared band carrier envelope phase (hereinafter referred to as CEP) stable optical parameter chirped pulse amplification (hereinafter referred to as OPCPA) laser system.

Background technique

In recent years, ultrashort pulse laser technology has developed rapidly. The continuous improvement of chirped pulse amplification (hereinafter referred to as CPA) technology and OPCPA technology has continuously narrowed the pulse width of ultrashort laser pulses. The output of ultra-short ultra-intense pulse. At present, research on ultrashort pulse systems is mainly limited to 800nm and 1064nm bands. Obtaining ultrashort pulses in the near-infrared band is of great significance in applications such as the generation of high-order harmonics in inert gases and ultra-high-speed optical communications.

The carrier envelope phase (CEP for short) of ultrashort pulses is defined as the relative phase between the pulse envelope peak and the electric field peak. The role of CEP is extremely important in the fields of attosecond pulse generation, optical atomic clocks, and quantum coherence control. CEP stabilization methods in ultrashort pulse laser systems can be divided into active and passive methods. The active CEP stabilization method is realized by measuring the carrier phase drift (CEO) of the system and feedback control (Nature Vol.421, No.6, 611-616, 2003). This method is very effective for the CEP stabilization of the femtosecond oscillator, but it is difficult to provide real-time measurement feedback in the kHz repetition rate high energy amplification method. Japan's A.Baltuska et al. proposed a method for realizing passive CEP stabilization using the difference frequency (difference frequency) process (Physical Review Letters, Vol.88, No.13, 133901, 2002). Based on this principle, C.Manzoni et al. in Italy proposed a CEP-stabilized Optical Parametric Amplification (OPA) pulsed laser system (Optics Express, Vol.14, No.21, 10109-10116), the optical path layout is shown in Figure 1. Femtosecond Ti:Sapphire Chirped Pulse Amplification (CPA) system 1 outputs an ultra-short and ultra-intense laser pulse sequence with a center wavelength of ~800nm, a single pulse energy of ~1.5mJ, and a pulse width of ~50fs. A part of the pulse sequence (~250μJ) is input into the CEP stable signal pulse generation part 6, and the other part (~1.25mJ) is divided into two parts after passing through the beam splitter 8, which are respectively used as pump light for the two-stage OPA process. The pulse sequence entering the CEP stable signal pulse generating part 6 is firstly spectrally broadened by the nonlinear effect in the hollow fiber 3, and the broadened pulse is compressed in the time domain by the chirped mirror 4 and then passes through the barium metaborate (abbreviated as BBO) crystal 5 The type II phase-matching difference frequency process obtains CEP stable near-infrared signal pulses. The signal light obtained in the frequency difference process is directly input into the OPA amplifier stage 14 for amplification, and the amplified CEP stable femtosecond pulse output is obtained through the femtosecond pulse pumping non-collinear OPA process in the two-stage BBO crystals 11 and 13 .

Due to the limited spectral broadening capability in the hollow-core fiber, the system requires a femtosecond Ti:Sapphire CPA laser system that outputs high-energy pulses as a pre-stage. And the femtosecond pulse pumping non-collinear OPA process in the BBO crystal is used in the amplification stage to amplify the signal pulse, which has high requirements for the synchronization adjustment accuracy of the system, and the output power of the system is affected by the signal pulse width and the pump pulse Energy constraints are also quite limited. In addition, the tuning of the wavelength is realized by rotating the crystal angle, which has a great influence on the subsequent optical path, and it is not easy to control accurately.

Contents of the invention

The purpose of this utility model is to provide an optical parametric chirped pulse amplification laser system for the above-mentioned deficiencies in the prior art. laser.

The principle of the utility model is to use the nonlinear photonic crystal fiber (PCF) to perform high-efficiency spectral conversion on part of the energy of the femtosecond pulse output by the Ti:sapphire mode-locked oscillator, and then based on the collinear alignment in the periodically polarized lithium niobate crystal The phase-matching difference frequency process is used to obtain CEP stable signal light with tunable near-infrared wavelength. The signal light is amplified by means of all-optical synchronous narrow-band pump OPCPA. The precise tuning of the signal wavelength is achieved by controlling the temperature of the periodically poled lithium niobate crystal.

The technical solution of the present utility model is as follows:

An optical parametric chirped pulse amplification laser system is characterized in that it includes a titanium sapphire femtosecond mode-locked pulse oscillator, a first beam splitter, a CEP stable signal pulse source, an OPCPA synchronous pump source, an OPCPA amplifier stage and a compressor, Its positional relationship is as follows: the direction of the output beam of the titanium sapphire femtosecond mode-locked pulse oscillator is the first beam splitter, which divides the laser beam into a transmitted beam and a reflected beam, and in the direction of the transmitted beam The CEP stable signal pulse source, OPCPA amplification stage and compressor are followed in turn, and the CEP stable signal pulse source is composed of a coaxial photonic crystal fiber, a chirped mirror, a periodically poled lithium niobate crystal and a stretcher ; The OPCPA amplification stage is sequentially composed of the first dichroic mirror, the first nonlinear crystal, the second dichromatic mirror and the second nonlinear crystal along the optical path; the OPCPA synchronous pumping source is followed by the modulation along the optical path Composed of a Q-multiplied YAG laser, a narrowband Ti:sapphire regenerative amplifier, a second beam splitter, and a total reflection mirror; the reflected beam is injected into the resonant cavity of the narrowband Ti:sapphire regenerative amplifier for amplification, and after being amplified, passes through the The second beam splitter and the total reflection mirror are respectively injected into the OPCPA amplification stage through the first dichroic mirror and the second dichroic mirror for synchronous pumping.

The working steps of the laser system of the present utility model are as follows:

1) The titanium sapphire femtosecond mode-locked pulse oscillator generates an ultrashort pulse sequence with a center wavelength at 800nm, a single pulse energy of ~80nJ, and a pulse width of <50fs; the pulse sequence is divided into two parts by the first beam splitter and injected into the CEP respectively The stable signal pulse source and the OPCPA synchronous pump source are used to generate the signal pulse and pump pulse of the OPCPA amplifier stage.

2) After the pulse injected into the CEP stable signal pulse source undergoes the nonlinear spectral conversion in the photonic crystal fiber, a large part of the energy is transferred to about 550nm, and the spectrally converted pulse is time-domain compressed with a chirped mirror, and then passed The difference frequency process of the 550nm component and the 850nm component in the periodically poled lithium niobate crystal obtains a CEP stable broadband difference frequency signal with a center wavelength near 1550nm, and then passes through a stretcher to obtain a signal pulse of the OPCPA amplifier stage. In the difference frequency process, the temperature tuning of the center wavelength of the difference frequency signal can be realized within a certain range by controlling the temperature of the periodically poled lithium niobate crystal.

3) The pulses input into the OPCPA synchronous pumping source pass through the narrow-band regenerative amplifier pumped by the Q-switched frequency multiplier YAG laser, and then output a narrow-band high-energy long pulse sequence with a center wavelength of 800nm, which is divided into two parts by the second beam splitter The two parts are respectively used as pump light for two-stage OPCPA amplification.

4) The signal light output from the CEP stable signal pulse source is directly incident and enters the nonlinear crystal through the dichroic mirror and the 800nm pump light for high-gain preamplification. The signal light amplified for the first time passes through another dichroic mirror It is fully amplified with another beam of pump light incident on the nonlinear crystal;

5) The amplified signal pulse is compressed to ~30fs level by a compressor, and a stable ultrashort pulse output of CEP in the near-infrared band is obtained.

In summary, compared with the prior art, the utility model has the following remarkable features:

1) A nonlinear photonic crystal fiber with a special structure is used to convert the pulse spectrum, and a periodically poled lithium niobate crystal is used as a difference frequency device, so that a CEP stable near-infrared pulse can be obtained with an nJ-level oscillator femtosecond pulse Broadband signal light; in the prior art, femtosecond light of the order of hundreds of μJ is required to obtain CEP stable signal light, and the conversion efficiency is low;

2) By tuning the temperature of the difference frequency periodic poled lithium niobate crystal, the tuning of the central wavelength of the output pulse can be easily realized within a certain range;

3) The amplification method of all-optical synchronous narrow-band pump OPCPA is adopted in the amplification stage, which can effectively obtain high-gain amplification; while the prior art adopts the amplification form of non-collinear broadband femtosecond optical pump OPA in BBO crystal, The pulse energy that can be obtained is limited.

Description of drawings

Fig. 1 is a schematic structural diagram of a tunable near-infrared CEP stabilized OPA ultrashort pulse laser system in the prior art.

Fig. 2 is a structural schematic diagram of the optical parametric chirped pulse amplification laser system of the present invention.

Fig. 3 is the spectrum converted by the photonic crystal fiber in the embodiment of the utility model.

Fig. 4 is the CEP stable difference frequency signal spectrum calculated in the embodiment of the present invention.

Fig. 5 is the gain spectrum of the first stage OPCPA process in the embodiment of the present invention.

Detailed ways

Below in conjunction with embodiment and accompanying drawing, the utility model is further described.

Please refer to Fig. 2 first, Fig. 2 is a structural schematic diagram of the optical parametric chirped pulse amplification laser system of the present utility model. It can be seen from the figure that the optical parametric chirped pulse amplification laser system of the present invention consists of a titanium sapphire femtosecond mode-locked pulse oscillator 15, a first beam splitter 16, a CEP stable signal pulse source 21, an OPCPA synchronous pump source 24, and an OPCPA Amplifying stage 30 and compressor 32 are made up of, and its position relation is as follows: the output beam direction of this titanium sapphire femtosecond mode-locked pulse oscillator 15 is the first beam splitter 16, and this first beam splitter 16 divides laser beam into transmission Light beam and reflected light beam, described CEP stable signal pulse source 21, OPCPA amplifying stage 30 and compressor 32 are successively in described transmission beam direction, and described CEP stable signal pulse source 21 is formed by the photonic crystal fiber of coaxial 17. A chirped mirror 18, a periodically poled lithium niobate crystal 19, and a stretcher 20 are formed; the OPCPA amplification stage 30 is composed of a first dichroic mirror 26, a first nonlinear crystal 27, and a second dichroic mirror in sequence along the optical path 28 and the second nonlinear crystal 29; the OPCPA synchronous pumping source 24 is sequentially composed of a Q-switched frequency-multiplied YAG laser 22, a narrowband titanium sapphire regenerative amplifier 23, a second beam splitter 25 and a total reflection mirror along the optical path 31; the reflected light beam is injected into the resonant cavity of the narrow-band Ti:sapphire regenerative amplifier 23 for amplification, and after amplification, the second beam splitter 25 and the total reflection mirror 31 are respectively passed through the first described first The dichroic mirror 26 and the second dichroic mirror 28 are injected into the OPCPA amplifier stage 30 for synchronous pumping.

As mentioned above, the laser system mainly includes the following parts: titanium sapphire femtosecond mode-locked pulse oscillator 15, beam splitter 16, CEP stable signal pulse source 21, OPCPA synchronous pump source 24, OPCPA amplifier stage 30, compressor 32 . The Ti:Sapphire femtosecond mode-locked oscillator 15 outputs an ultrashort pulse sequence with a center wavelength at 800nm, a single pulse energy of ~80nJ, and a pulse width <50fs. The pulse sequence is divided into two parts by the first beam splitter 16 and injected into the CEP stable The signal pulse source 21 and the OPCPA synchronously pump the source 24 . The CEP-stabilized signal pulse source 21 generates CEP-stabilized broadband OPCPA signal light with a center wavelength near 1.55 μm. Among them, the photonic crystal fiber 17 transfers most of the energy of the input 800nm femtosecond pulse to the main peak of the spectrum at 550nm; the pulse compressed in the time domain by the chirped mirror 18 undergoes a difference frequency process in the periodically poled lithium niobate crystal 19, Since the pump light and signal light in the difference frequency process come from the same broadband pulse, the phase of the output idler light will remain constant to achieve CEP stability. When the pump light loss is ignored, the difference frequency process can be calculated by the following coupling equation describe:

$\frac{{\mathrm{<span\; class="notranslate">\; D</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}}{\mathrm{<span\; class="notranslate">\; dz</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; i\&kappa;</span>}}_{\mathrm{<span\; class="notranslate">\; DF</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{<span\; class="notranslate">\; *</span>}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; iz\&Delta;k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

$\frac{{\mathrm{<span\; class="notranslate">\; D</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}{\mathrm{<span\; class="notranslate">\; dz</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; i\&kappa;</span>}}_{\mathrm{<span\; class="notranslate">\; DF</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{<span\; class="notranslate">\; *</span>}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; iz\&Delta;k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

The subscripts i, s, and p represent idler light, signal light, and pump light, respectively, A is the optical field variable, κ _DF is the coupling coefficient of the difference frequency process, Δk is the phase mismatch, and z is the light propagating in the crystal. distance.

The wideband pulse after the frequency difference is stretched by the stretcher 20 and then input as a signal pulse to the OPCPA amplification stage 30 for amplification. The OPCPA synchronous pumping source 24 generates a narrow-band ps-level pulsed laser with a center wavelength of 800 nm, wherein the narrow-band regenerative amplifier 23 is pumped by a Q-switched frequency-multiplied YAG laser 22 . The laser pulse output by the narrow-band regenerative amplifier 23 is divided into two parts by the second beam splitter 25, which are respectively used as pump light for two-stage OPCPA amplification. The OPCPA amplification stage 30 is mainly composed of nonlinear crystals 27 and 29, and the amplified signal pulse is compressed by the compressor 32 to the order of ~30 fs, so as to obtain a stable ultrashort pulse output of CEP in the near-infrared band. The gain in the OPCPA amplifier stage can be described by the following equation:

G＝1+(ξL) ² (sinh B/B) ² (3)

Where: G is the signal light gain, $B=\sqrt{{\left(\mathrm{\&xi;L}\right)}^2-{(\mathrm{\&Delta;kL}/2)}^2},$ ξ is the small signal gain, L is the crystal thickness, and Δk is the phase mismatch.

The structure of this embodiment is shown in FIG. 2 . A Ti:Sapphire femtosecond mode-locked pulse oscillator 15 capable of outputting a pulse width of ~50 fs and a single pulse energy of ~80nJ at a center wavelength of 800nm is used, and is divided into two parts of ~10nJ and ~70nJ through the first beam splitter 16. The former is injected into the synchronous pump source 24 of the OPCPA amplification stage as seed light for narrow-band amplification, and the latter is injected into the OPCPA signal light generation system 21 . After injecting a 70nJ pulse through the nonlinear spectral conversion in the photonic crystal fiber 17, the supercontinuum output with an energy ~ 10nJ spectral shape as shown in Fig. ultrashort pulse. Through the difference frequency process in the periodically polarized lithium niobate crystal 19 with a thickness of 1mm, a stable pulse output of CEP with a center wavelength of about 1550nm and an energy of ~5pJ can be obtained, and a signal of ~5ps can be obtained after the stretching effect of the prism on the stretcher 20 pulse. The shape of the idle light spectrum of the difference frequency process calculated according to equations (1) and (2) is shown in Fig. 4 . OPCPA amplification stage synchronous pump source 24 adopts Q-switched frequency multiplied YAG laser 22 with output wavelength 532nm to pump narrowband Ti:sapphire regenerative amplifier 23, and outputs ~5mJ (10ps) 800nm narrowband pulse as OPCPA pumping light incident to OPCPA amplification Level 30 middle. Two-stage amplification is adopted in the OPCPA amplification stage 30: a 3mm-thick periodically poled lithium niobate crystal 27 is used in the first-stage amplification to obtain high-gain amplification, and a signal amplification output of ~1 μJ can be obtained under a pump energy of 100 μJ. According to the equation (3) The calculated gain spectrum of the first-stage OPCPA process is shown in Figure 5; the second-stage amplification uses a 5mm-thick lithium triborate (LBO) crystal29, and can obtain ~0.5mJ at a pump energy of 4.9mJ 1550nm broadband chirped pulse output. Finally, after passing through the compressor 32, a stable ultrashort pulse output of mid-infrared CEP with pulse energy > 0.2mJ and pulse width ~ 30fs can be obtained.

Claims (1)

1. optical parameter chirp impulse amplification laser system, it is characterized in that by titanium jewel femtosecond mode locking pulse oscillator (15), first beam splitting chip (16), CEP stabilization signal impulse source (21), OPCPA synchronous pump source (24), OPCPA amplifier stage (30) and compressor reducer (32) are formed, its position relation is as follows: the output beam direction at this titanium jewel femtosecond mode locking pulse oscillator (15) is first beam splitting chip (16), this first beam splitting chip (16) is divided into transmitted light beam and folded light beam with laser beam, in described transmitted light beam direction is described CEP stabilization signal impulse source (21) successively, OPCPA amplifier stage (30) and compressor reducer (32), described CEP stabilization signal impulse source (21) is by the photonic crystal fiber (17) with optical axis, chirped mirror (18), periodically poled lithium niobate crystal (19) and stretcher (20) constitute; Described OPCPA amplifier stage (30) is made up of first dichroic mirror (26), first nonlinear crystal (27), second dichroic mirror (28) and second nonlinear crystal (29) successively along light path; Described OPCPA synchronous pump source (24) is made up of q-multiplier YAG laser instrument (22), arrowband titanium jewel regenerative amplifier (23), second beam splitting chip (25) and total reflective mirror (31) successively along light path; The resonator cavity that described folded light beam is injected described arrowband titanium jewel regenerative amplifier (23) amplifies, and amplifies after described second beam splitting chip (25) and total reflective mirror (31) carry out synchronous pump through described first dichroic mirror (26) and second dichroic mirror (28) the described OPCPA amplifier stage of injection (30) respectively.

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