CN103234643A - Method for measuring carrier-envelop phase positions of few-circle femtosecond laser pulses - Google Patents

Abstract

Disclosed is a method for measuring carrier-envelop phase positions of few-circle femtosecond laser pulses. The method includes the steps of arranging a device, measuring and calculating the absolute value of a laser carrier-envelope phase position to be measured. By the method, accuracy of the carrier-envelop phase positions of the few-circle femtosecond laser pulses can be directly measured, and a reliable route is provided for measuring the absolute value of the carrier-envelop phase positions.

Description

The measuring method of the carrier wave-envelope phase of cycle magnitude femto-second laser pulse

Technical field

The invention belongs to femtosecond optical measurement field, particularly a kind of measuring method of carrier wave-envelope phase of cycle magnitude femto-second laser pulse.

Background technology

Important parameter-carrier wave-envelope phase (Carrier-envelop Phase of cycle magnitude (duration of pulse has only several optical cycles) laser pulse, be designated hereinafter simply as CEP), refer to the relative phase between the maximal value of electric field vibration under the maximal value of pulse envelope and the envelope, its determines the instantaneous electric field intensity of laser pulse.In few-cycle laser pulse and the matter interaction process, CEP has decisive influence, the synthetic and relevant control of for example generation of higher hamonic wave and chirped pulse, optics etc.Especially in Ah second's science and opctical frequency standard surveying field, CEP is bringing into play very important effect.Along with deepening continuously of frequency marking surveying and Ah second's scientific research, control and measuring period the magnitude femto-second laser pulse CEP, become one of research contents of current forefront.

People such as G.G.Paulus are once at article " Measurement of the Phase of few-cycle laser Pulses " [Phys.Rev.Lett.91, the method of a kind of solid ionization mass spectrometer measurement above threshold CEP is proposed 253004 (2003)], by the measurement to photoelectron spectrum, utilize the left and right sides asymmetry of ionization productive rate on the threshold value to come the CEP of magnitude laser pulse measuring period.This measurement scheme requires complicated ultrahigh vacuum device, and the experiment difficulty is bigger, and because measure theory is not mature enough, fails extensively to be admitted.For example classical with the Keldysh-tyPe model prediction be symmetrical for the pulse left and right sides productive rate of longitudinal cosine type, be different with experimentally result.In addition, people such as C.A.Haworth once proposed in the article " Half-cycle cutoffs in harmonic spectra and robust carrier-envelope phase retrieval " [Nature Physics3,52 (2007)] to utilize the higher hamonic wave radiation of each half period of laser pulse and the correlativity of the CEP of light field herein to measure the CEP of laser; People such as M.Kre β propose to measure based on the correlativity of the asymmetric theoretical THz wave amplitude that produces of photoionization and CEP the CEP of laser in article " Determination of the Carrier-Envelope Phase of Few-Cycle Laser Pulses with Terahertz-Emission Spectroscopy " [Nature Physics2,327 (2006)].

Said method has been ignored focusing and nonlinear effect to the influence of CEP value, and theoretical and experiment shows that all the nonlinear effect in light field and the medium interaction process is very big to the influence of CEP, can not ignore.Therefore, existing CEP measuring method is all perfect inadequately.

Summary of the invention

The object of the present invention is to provide a kind of measuring method of carrier wave-envelope phase of cycle magnitude femto-second laser pulse, that this method is measured is the initial CEP of laser, be not subjected to focus on and the restriction of nonlinear effect ground, do not need complex appts such as ultrahigh vacuum, be not subjected to the limitation of harsh experiment condition.

Technical solution of the present invention is as follows:

A kind of measuring method of carrier wave-envelope phase of cycle magnitude femto-second laser pulse is characterized in that this method comprises the following steps:

1. setting device: the laser that ti sapphire laser comes out is divided into transmitted light and reflected light through beam splitting chip, and described reflected light incides through second total reflective mirror, chronotron, second lens and closes the bundle sheet; Described transmitted light is through optical parameter amplification system, first lens, hollow optic fibre, produce behind the silicon chip CEP stable treat photometry, on the working direction of described testing laser, perpendicular to described testing laser light beam quartzy wedge is set, first total reflective mirror, this first total reflective mirror will treat that the photometry reflection focuses on the generation chevilled silk through spherical mirror, the THz wave that this chevilled silk produces focuses on through parabolic lens closes the bundle sheet, this Terahertz sees through described bundle sheet and the described reflected light of closing and restraints the sheet beam reflected and merge into a branch of being called and close Shu Guang through described closing, this closes Shu Guang by crystal detection, half-wave plate, the balance detection device that wollaston prism and balance detector constitute is surveyed, described beam splitting chip, second total reflective mirror, each is 45 ° with the light beam of injecting to parabolic lens with closing the bundle sheet, and described crystal detection is positioned at the common focus place of described second lens and parabolic lens;

2. measure: the insertion amount of the insertion testing laser bundle of quartzy wedge is little when initial, the hot spot for the treatment of photometry is just in time passed through, testing laser focuses in air through described spherical mirror and produces chevilled silk, this chevilled silk produces THz wave, foil is installed on the translation stage, make described foil from the initiating terminal of chevilled silk, with the interval of 0.5mm along the length direction of described chevilled silk continuously the mobile foil that is installed in translation stage at the diverse location of the chevilled silk silk that is in the light, end until chevilled silk, the reflected light of described beam splitting chip is as surveying light, close bundle with the THz wave that reflects through described parabolic lens, utilize the described THz wave waveform of described balance detection device recording; Increase continuously the insertion amount of described quartzy wedge, continuously changing the CEP of testing laser, Terahertz waveform and the counter-rotating result thereof of different chevilled silks position when described balance detection device records different CEP;

3. the step of absolute value of calculating CEP is as follows:

A) look for the rollback point of Terahertz waveform from described Terahertz waveform and counter-rotating result thereof, the CEP of the testing laser of correspondence was 0.5 π when first Terahertz waveform rollback point disappeared;

The insertion amount Δ l of the quartzy wedge of correspondence when b) measuring first Terahertz waveform rollback point disappearance;

C) calculate the CEP change amount that quartzy wedge insertion amount Δ l causes by following formula

Wherein, ω is light frequency to be measured, and u treats the photometry group velocity, and v treats the photometry phase velocity, and λ is light wavelength to be measured, and n is quartzy wedge (7) refractive index, and c is light speed in a vacuum, and

$u=v-\mathrm{\λ}\frac{\mathrm{dv}}{\mathrm{d\λ}}=v(1+\frac{\mathrm{\λ}}{n}\·\frac{\mathrm{dn}}{\mathrm{d\λ}}),$ $n=1.4974,\frac{\mathrm{dn}}{\mathrm{d\λ}}=-0.0138;$

D) absolute value of the CEP of testing laser

Advantage of the present invention:

1. the present invention adopts laser to produce chevilled silk in air and measures the Terahertz waveform, utilize the counter-rotating of Terahertz waveform and CEP correlativity to judge the CEP of driving laser, experimental phenomena can distinguish intuitively that in measuring process experimental provision is simple, do not need high-vacuum installation and complex apparatus, operability is good.

2. test the minimum only 0.2mJ of required laser energy, have application prospect widely.

What 3. the present invention measured is the initial CEP value of laser, is not focused on the influence with other nonlinear effect, more accurately and reliably.

Description of drawings

Fig. 1 is sniffer structural representation of the present invention.

Fig. 2 is the different CEP(π of the present invention scope) following THz wave reversal of poles synoptic diagram.

Fig. 3 is the CEP decision flowchart.

Embodiment

The present invention will be further described below in conjunction with drawings and Examples, but should therefore not limit protection scope of the present invention.

1. see also Fig. 1 earlier, Fig. 1 involves THz wave sniffer structural representation for the Terahertz that laser air of the present invention becomes silk to produce the waveform counter-rotating.As seen from the figure, the laser that is come out by ti sapphire laser 1 is divided into transmitted light beam and folded light beam through beam splitting chip 2 with laser, described folded light beam is through total reflective mirror 12 reflections, chronotron 13, behind the lens 14, incide and close bundle sheet 15, described transmitted light is through optical parameter amplification system 3, lens 4, hollow optic fibre 5, silicon chip 6 back produce have CEP stable treat photometry, quartzy wedge 7 is set on the working direction of described testing laser, first total reflective mirror 8, this total reflective mirror 8 reflects the laser light to spherical mirror 9 and focuses on the generation chevilled silk, the Terahertz that this chevilled silk produces focuses on through parabolic lens 11 and closes bundle sheet 15, closing bundle sheet 15 beam reflected with this merges into a branch of, inject in the crystal detection 16, through crystal detection 16, half-wave plate 17, the balance detection device that wollaston prism 18 and balance detector 19 constitute is surveyed, described beam splitting chip 2, total reflective mirror 12, parabolic lens 11, close bundle sheet 15 and be 45 ° with the light beam of injecting, described crystal detection 16 is positioned at the common focus place of described lens 14 and parabolic lens 11; Illustration indicates the wedge parameter in apparatus of the present invention, and the length of side is L, and height is h, and drift angle is a.

The principle of work of device: (centre wavelength is 800nm to the laser that ti sapphire laser 1 comes out, pulse width 25fs, repetition frequency 1kHz, the output energy is 5.2mJ), through beam splitting chip 2 laser is divided into transmitted light beam and folded light beam, transmitted light beam is through optical parameter amplification system 3, first lens 4 focus on, hollow optic fibre compressor reducer 5 compressed pulse widths, silicon chip 6 dispersion compensations produce cycle magnitude femtosecond pulse (the centre wavelength 1800nm of the stable infrared wavelength of CEP, pulse width 11fs is about 1.8 optical cycles, the output energy is 0.45mJ), the insertion amount that changes quartzy wedge 7 continuously changes the CEP of testing laser, for example increase continuously in the cycle or reduce CEP at 2 π with the interval of 0.1 π, reflect the laser light to spherical mirror 9 through first total reflective mirror 8 and be focused into chevilled silk generation THz wave, this THz wave focuses on through parabolic lens 11 and closes bundle sheet 15; Light is surveyed in reflected light (centre wavelength 800nm) conduct through described beam splitting chip 2, merge into Shu Guang at the described bundle sheet 15 that closes with transmitted light beam (centre wavelength 1800nm) through chronotron 13, second lens 14, this closes Shu Guang and injects in the Terahertz crystal detection 16, surveys through described balance detection device 19.Along on the direction of propagation of chevilled silk, the mobile foil 10 that is installed in translation stage removes the silk that is in the light in different chevilled silk positions continuously, obtains becoming in difference the Terahertz inversion waveforms of silk position.As shown in Figure 1, the polarity of the THz wave (1) that for example obtains at chevilled silk leading portion 4mm place under certain CEP is opposite with the polarity that moves to the THz wave (2) that the 7mm of chevilled silk back segment obtains when the moving metal sheet;

The concrete parameter of apparatus of the present invention embodiment is as follows:

Arrange light path as Fig. 1, the focal length of first lens 4 is 20cm, quartzy wedge 7 shown in the illustration among the figure, and drift angle a is 3 °, length of side L is 50mm, and high h is 2mm, and the stepper motor that quartzy wedge 7 is installed moves ⊿ d, CEP changes 0.1 π, when then CEP changes 2 π, and the displacement S=20 ⊿ d that stepper motor moves.The focal length of spherical mirror 9 is 15cm, produces the chevilled silk of about 12mm.Stop described chevilled silk with the about 0.2mm * 4mm of foil 10(* 20mm), the chevilled silk of back is disappeared, the THz wave that silk produces is not in the light in the record front, beam splitting chip 2, total reflective mirror 12, parabolic lens 11, close bundle sheet 15 and be 45 ° with the light beam of injecting, quartzy wedge and laser vertical are placed, chronotron 13 vertically is placed on the shifting sledge by the two sides total reflective mirror and constitutes, first mirror of this chronotron and total reflective mirror 12 parallel placements, the focal length of second lens 14 is 50cm, the focal length of parabolic lens 11 is 10cm, crystal detection 16 is placed on the common focus place of lens 14 and parabolic lens 11, and the thickness of crystal detection 16 is 1mm;

2. Fig. 2 is different CEP(π scopes among the present invention) rough schematic of THz wave reversal of poles down, THz wave reversal of poles result when energy is 250uJ.As shown in Figure 2, two kinds of gray scales represent the different polarity of Terahertz, and darker color represents the positive polarity of THz wave, and more shallow color represents the negative polarity of THz wave, and we are called rollback point with the THz wave waveform residing position of reversing.The rule that theoretical analysis and calculation obtains is: during CEP=0.0 π～0.4 π, the rollback point position of the Terahertz waveform of chevilled silk front end is to shift to the chevilled silk starting end gradually, and when CEP=0.5 π, the rollback point of the Terahertz waveform of chevilled silk front end disappears.But the step according to this rule visual interpretation CEP judgement: find the Terahertz waveform rollback point end point at the chevilled silk front end, the CEP of correspondence is 0.5 π when the chevilled silk initiating terminal, according to the wedge insertion amount of measuring, calculate CEP poor of testing laser and transmission laser before and after the wedge

Obtain the true value of the CEP of testing laser.

The insertion amount of measuring quartzy wedge 7 is Δ l, and then the CEP change amount that causes of quartzy wedge 7 insertion amount Δ l is

Wherein ω is light frequency to be measured, and u is the group velocity for the treatment of photometry, and v is the phase velocity for the treatment of photometry, and λ is light wavelength to be measured, and n is the refractive index of quartzy wedge (7), and c is light speed in a vacuum, and

$u=v-\mathrm{\λ}\frac{\mathrm{dv}}{\mathrm{d\λ}}=v(1+\frac{\mathrm{\λ}}{n}\·\frac{\mathrm{dn}}{\mathrm{d\λ}}),$ $n=1.4974,\frac{\mathrm{dn}}{\mathrm{d\λ}}=-0.0138;$

Obtain testing laser at last

Fig. 3 is CEP decision flowchart of the present invention.

Experiment shows, the present invention is not subjected to focus on and the restriction of nonlinear effect ground, do not need complex appts such as ultrahigh vacuum, be not subjected to the limitation of harsh experiment condition, directly measuring period the magnitude femto-second laser pulse the exact value of carrier wave-envelope phase, for the absolute value of measuring carrier wave-envelope phase provides reliable approach.

Claims (1)

1. the measuring method of the carrier wave-envelope phase of a cycle magnitude femto-second laser pulse is characterized in that this method comprises the following steps:

1. setting device: the laser that ti sapphire laser (1) comes out is divided into transmitted light and reflected light through beam splitting chip (2), and described reflected light incides through second total reflective mirror (12), chronotron (13), second lens (14) and closes bundle sheet (15); Described transmitted light is through optical parameter amplification system (3), first lens (4), hollow optic fibre (5), silicon chip (6) back produce CEP stable treat photometry, on the working direction of described testing laser, perpendicular to described testing laser light beam quartzy wedge (7) is set, first total reflective mirror (8), this first total reflective mirror (8) will treat that the photometry reflection focuses on the generation chevilled silk through spherical mirror (9), the Terahertz that this chevilled silk produces converges to through parabolic lens (11) and closes bundle sheet (15), this Terahertz sees through described bundle sheet (15) and the described reflected light of closing and merges into a branch of being called and close Shu Guang through described bundle sheet (15) beam reflected of closing, this closes Shu Guang by crystal detection (16), half-wave plate (17), the balance detection device that wollaston prism (18) and balance detector (19) constitute is surveyed, described beam splitting chip (2), second total reflective mirror (12), parabolic lens (11) and close the bundle sheet (15) each be 45 with the light beam of injecting ⁰, described crystal detection (16) is positioned at the common focus place of described second lens (14) and parabolic lens (11);

2. measure: the insertion amount of the insertion testing laser bundle of quartzy wedge (7) is little when initial, the hot spot for the treatment of photometry is just in time passed through, testing laser focuses in air through described spherical mirror (9) and produces chevilled silk, this chevilled silk produces THz wave, foil (10) is installed on the translation stage, make described foil (10) from the initiating terminal of chevilled silk, with the interval of 0.5mm along the length direction of described chevilled silk continuously the mobile foil (10) that is installed in translation stage at the diverse location of the chevilled silk silk that is in the light, end until chevilled silk, the reflected light of described beam splitting chip (2) is as surveying light, close bundle with the THz wave that reflects through described parabolic lens (11), utilize the described THz wave waveform of described balance detection device recording; Increase continuously the insertion amount of described quartzy wedge (7), continuously changing the CEP of testing laser, Terahertz waveform and the counter-rotating result thereof of different chevilled silks position during the different CEP of described balance detection device (19) record;

3. the step of absolute value of calculating testing laser CEP is as follows:

A) look for the rollback point of Terahertz waveform from described Terahertz waveform and counter-rotating result thereof, the CEP of correspondence was 0.5 π when first Terahertz waveform rollback point disappeared;

The insertion amount △ l of the quartzy wedge (7) of correspondence when b) measuring first Terahertz waveform rollback point disappearance;

C) calculate the CEP change amount that quartzy wedge (7) insertion amount △ l causes by following formula

Wherein, ω is light frequency to be measured, and u treats the photometry group velocity, and v treats the photometry phase velocity, and λ is light wavelength to be measured, and n is the refractive index of quartzy wedge (7), and c is light speed in a vacuum, and

$u=v-\mathrm{\λ}\frac{\mathrm{dv}}{\mathrm{d\λ}}=v(1+\frac{\mathrm{\λ}}{n}\·\frac{\mathrm{dn}}{\mathrm{d\λ}}),$ $n=1.4974,\frac{\mathrm{dn}}{\mathrm{d\λ}}=-0.0138;$

D) absolute value of the CEP of testing laser=0.5 π-

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