CN203216616U - Single signal-to-noise ratio measuring device based on chirp pulse characteristics - Google Patents

Abstract

The utility model is a single signal-to-noise ratio measuring device based on the characteristics of chirped pulses, which can measure the signal-to-noise ratio of a single pulse. The principle is to use the optical Kerr effect to construct the pump-detection optical path. The measurement device broadens the detection light into temporally and spatially chirped laser pulses through gratings or prisms. The detection light is transmitted from the analyzer due to the optical Kerr effect, and then the transmitted signal is collected by a scientific grade CCD to obtain the signal-to-noise ratio information of the laser pulse to be measured. The utility model introduces a large amount of negative dispersion through a grating or a prism, broadens the detection light pulse to hundreds of picoseconds or wider, and can make the time window reach hundreds of picoseconds or wider. Furthermore, the dynamic range can be increased finally by inserting a spatial light modulator in the detection optical path.

Description

Single SNR Measuring Device Based on Chirped Pulse Characteristics

technical field

The utility model is a single signal-to-noise ratio measuring device based on the characteristics of chirped pulses. the

Background technique

The interaction between ultra-short and ultra-intense laser pulses and matter is a strong field process. The pulse signal-to-noise ratio is a very important parameter that directly affects the interaction between laser and matter. The signal-to-noise ratio of ultra-short and ultra-intense laser pulses can be accurately measured. Ratio is crucial for strong-field physics. the

For the measurement of picosecond and femtosecond pulse signal-to-noise ratios, general-purpose electronic measurement techniques such as streak cameras cannot meet the needs, and the most commonly used measurement methods are techniques such as third-order autocorrelation. The triple correlation method uses a frequency multiplication and a sum frequency process to obtain a triple frequency signal, which can accurately measure noise information such as sub-pulse, leading edge, and trailing edge of the pulse. This method usually uses a scanning measurement method, which can be used to measure ultrashort pulses with high repetition frequency (above 10Hz) and stable energy output. However, when the pulse is amplified to the level of Joules and the intensity reaches the level of Pawatts, the repetition rate is low, and it is usually a single pulse. For such a single-operation ultra-powerful laser device, a single measurement must be used. the

The current single-shot measurement system is usually based on triple frequency or difference-frequency correlation, using various methods to replicate the single pulse or different delay times, and finally achieve a single measurement, usually the detectable time window is only tens of picoseconds . the

The optical Kerr effect is an effect caused by the third-order nonlinearity of the medium, and has been widely used in pump-probe experiments of ultrashort pulses. The optical Kerr effect can be expressed as:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; OKS</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; probe</span>}}{\mathrm{<span\; class="notranslate">\; sin</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; sin</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;\&phi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>$

I _OKS is the transmitted light intensity of the optical Kerr effect, _Iprobe is the probe light intensity, θ is the angle between the polarization directions of the pump light and the probe light, and Δφ is the nonlinear phase shift. When the nonlinear phase shift is small, it can be approximated as

Contents of the invention

The purpose of this utility model is to provide a single signal-to-noise ratio measurement device based on chirped pulse characteristics, which overcomes the shortcoming of the existing single signal-to-noise ratio measurement device with a narrow time window (generally tens of picoseconds), This device can measure hundreds of picoseconds at a time. the

The technical solution of the utility model is:

A single signal-to-noise ratio measurement method based on pulse chirp characteristics, comprising the following steps,

(1) Generate an optical Kerr signal;

(2) The CCD collects the optical Kerr signal to obtain the distribution of light intensity in space;

(3) Calculate the signal-to-noise ratio according to the distribution information of light intensity in space;

Its special feature is that the specific steps for generating the optical Kerr signal in step (1) are:

(1.1) Divide the laser to be tested into two beams, one as pump light and the other as probe light;

(1.2) The probe light is broadened by the stretching device into temporally chirped and spatially chirped pulses, and after the stretched pulses pass through the first polarizer, they are focused into the nonlinear medium;

(1.3) The pump light passes through the optical delay device, and then adjusts the polarization direction of the pump light through a half-wave plate, so that the angle formed between the polarization direction of the pump light and the polarization direction of the probe light is a, a≠90°, and focused to In nonlinear media;

(1.4) Adjust the optical delay device to make the pump light and probe light reach the nonlinear medium synchronously, that is, to make the pump light and probe light overlap in time; adjust the inclination angle and position of each device on the pump light optical path so that the probe light and probe light The focus of the pump light coincides in the nonlinear medium, that is, the pump light and the probe light coincide in space;

(1.5) After the probe light passing through the nonlinear medium is collimated, it passes through the second polarizer. The transmission polarization direction of the second polarizer is perpendicular to the transmission polarization direction of the first polarizer, and can transmit the second polarization The optical signal of the device is the optical Kerr signal. the

The stretching device includes a grating pair composed of two identical gratings or a prism pair composed of two identical triangular prisms, the first grating of the grating pair is set on the optical path of the probe light, and the second grating is set on the first grating On the diffraction optical path of the second grating, the first polarizer is arranged on the outgoing optical path of the second grating; the pair of prisms are arranged in the same way. the

The gratings are reflective or transmissive. the

A prism is a prism with dispersion properties. the

A single signal-to-noise ratio measurement device based on pulse chirp characteristics, including a beam splitting device that divides the laser light to be measured into pump light and probe light, and a stretching device that broadens the probe light. The special feature is that the stretching device It includes a grating pair composed of two identical gratings or a prism pair composed of two identical prisms, the first grating of the grating pair is set on the optical path of the probe light, and the second grating is set on the diffracted light of the first grating on the road; the pair of prisms are arranged in the same way. The first polarizer is arranged on the outgoing light path of the second grating, and the pulse after stretching is focused into the nonlinear medium through the first polarizer. the

The measurement device also includes a spatial light modulator or an attenuation element arranged between the stretching device and the CCD, and the spatial light modulator or attenuation element is used to attenuate the strong signal detected on the CCD by a fixed multiple to prevent the phase surface of the CCD from Saturation, which increases the detectable dynamic range. the

CCD selects scientific grade CCD. the

The nonlinear medium is a liquid or solid material with a large third-order nonlinear coefficient. Preferably, the nonlinear medium is CS ₂ , bismuthate glass or tellurite glass.

The polarizer is a polarizing prism or a polarizer. the

The polarizer is a Nikkor prism, a Glan prism, a Glan-Taylor prism, or a Wollaston prism. the

可知，CCD上各点归一化的I_OKS与I_probe强度分布开方后就反映了待测激光脉冲（即泵浦光）的信噪比信息。  The principle of the utility model is to use the optical Kerr gate effect to construct the pumping detection optical path. The measuring device expands the detection light into laser pulses chirped in time and in space through a grating or a prism; chirp can be selected in the measurement process The half-width region of the chirp pulse is used as the measurement window. When the pump light forms an optical Kerr gate in the nonlinear medium, it forms a temporal gating signal for the probe light, that is, the third-order nonlinearity of the nonlinear medium produces a polarization rotation for the time-synchronous part of the probe light. Finally, through the analyzer, the transmitted signal is collected by a scientific-grade CCD, and the spatial distribution of the light intensity I _OKS is obtained. Depend on

It can be seen that the square root of the normalized I _OKS and I _probe intensity distribution at each point on the CCD reflects the signal-to-noise ratio information of the laser pulse to be measured (that is, the pump light).

The utility model has the advantages of:

(1) This device introduces a large amount of dispersion through a widening device such as a grating or a prism, and broadens the detection light pulse to hundreds of picoseconds or wider, which can make the time window of a single signal-to-noise ratio measurement device reach hundreds of picoseconds above. the

(2) The time resolution of the device for measuring SNR is determined by the response time of the nonlinear medium and the spatial resolution of the CCD. Therefore, choosing nonlinear media with fast response time such as bismuthate glass or tellurite glass (response time can reach femtosecond level) is conducive to improving the time resolution of signal-to-noise ratio measurement; choosing high spatial resolution and large lateral The size of the CCD is conducive to the improvement of time resolution and time window. the

(3) The dynamic range of the device for measuring SNR depends on the extinction ratio of the first polarizer and the second polarizer and the dynamic range of the CCD. Therefore, when the two polarizers are adjusted to be strictly perpendicular, it is required that the extinction ratio of the first polarizer and the second polarizer be as high as possible, usually higher than 10 ⁵ ; at the same time, the larger the dynamic range of the CCD, the better.

(4) Insert a spatial light modulator or an attenuation element between the stretching device and the CCD to attenuate the part with a strong detection signal intensity on the CCD at a fixed multiple to prevent the saturation of the CCD phase surface and increase the detectable signal-to-noise ratio dynamic range. the

Description of drawings

Fig. 1 Schematic diagram of signal-to-noise ratio measurement using chirped pulse characteristics;

Fig. 2 uses the pulse laser SNR measuring device diagram of grating pair;

Fig. 3 Schematic diagram of pulsed laser signal-to-noise ratio measurement device using a prism pair. the

Among them: 1-pulse laser; 2-beam split; 3-aperture aperture; 4-grating; 5-prism; 6-first polarizer; 7-first focusing lens; 8-nonlinear medium; 9-quasi Straight lens; 10-second polarizer; 11-CCD; 12-half-wave plate; 13-second focusing lens. the

Detailed ways

The principle of the utility model is to use the optical Kerr gate effect to construct the pump detection optical path. The measuring device broadens the detection light into a chirped laser pulse in time and space through a grating or a prism; and the pump light is to be The compressed ultrashort pulse measured is usually a picosecond or femtosecond pulse, as shown in Figure 1. During the measurement process, the half-width region of the chirped pulse can be selected as the measurement window (see the area in the dotted line box in Figure 1) . When the pump light forms an optical Kerr gate in the nonlinear medium, it forms a temporal gating signal for the probe light, that is, the third-order nonlinearity of the nonlinear medium produces a polarization rotation for the time-synchronous part of the probe light. Finally, through the analyzer, the transmitted signal is collected by a scientific grade CCD, and the spatial distribution of the Kerr signal light intensity I _OKS is obtained. Depend on It can be seen that the square root of the normalized I _OKS and I _probe intensity distribution at each point on the CCD reflects the signal-to-noise ratio information of the laser pulse to be measured (that is, the pump light).

A single signal-to-noise ratio measurement method based on pulse chirp characteristics, comprising the following steps:

(1) Generate optical Kerr signal:

(1.1) Divide the laser to be tested into two beams, one as pump light and the other as probe light;

(1.2) After the probe light passes through the pinhole diaphragm, it is broadened into temporally chirped and spatially chirped pulses by the stretching device, and the stretched pulses pass through the first polarizer, and then focus into the nonlinear medium;

(1.3) The pump light passes through the optical delay device, and then adjusts the polarization direction of the pump light through the half-wave plate, so that the angle formed by the polarization direction of the pump light and the polarization direction of the probe light is a, a≠90°, and a is equal to 45° is the best, focusing into the nonlinear medium;

(1.4) Adjust the optical delay device to make the pump light and probe light reach the nonlinear medium synchronously, that is, to make the pump light and probe light overlap in time; adjust the inclination angle and position of each device on the pump light optical path so that the probe light and probe light The focus of the pump light coincides in the nonlinear medium, that is, the pump light and the probe light coincide in space;

(1.5) After the probe light passing through the nonlinear medium is collimated, it passes through the second polarizer. The transmission polarization direction of the second polarizer is perpendicular to the transmission polarization direction of the first polarizer, and can transmit the second polarization The optical signal of the device is the optical Kerr signal. the

(2) The CCD collects the optical Kerr signal to obtain an image of the spatial distribution of light intensity;

(3) Measure the broadened chirped pulse width, spectrum, and spectral components corresponding to the positions of each point on the CCD lateral direction. The time coordinates of the CCD pixel and the optical Kerr signal can be corresponding, and the distribution of light intensity on the CCD lateral pixel corresponds to The distribution of the signal-to-noise ratio over time, from which the measurement result of the signal-to-noise ratio is obtained. the

In order to increase the measurement dynamic range of the device, a spatial light modulator or an attenuating element can be inserted between the stretching device and the CCD to attenuate the part with a strong detection signal intensity on the CCD by a fixed multiple to prevent the saturation of the CCD phase surface. Increases the dynamic range over which the signal-to-noise ratio can be detected. At this time, in step 3, the attenuated signal should also be restored, and the restoration method is a known method. the

The stretching device includes a grating pair composed of two identical gratings or a prism pair composed of two identical prisms, the first grating of the grating pair is set on the optical path of the probe light, and the second grating is set on the first On the diffraction optical path of the grating, the first polarizer is arranged on the outgoing optical path of the second grating; the prism pair is also arranged on the same. the

The device introduces a large amount of dispersion through a grating or a prism, broadens the detection light pulse to hundreds of picoseconds or more, and can make the time window reach more than hundreds of picoseconds. the

Scheme 1 of the device of the present utility model is shown in Fig. 2, the laser light emitted by the pulse laser 1 is a compressed short pulse, which is divided into two beams by a beam splitter, the beam splitter is a beam splitter 2, and one of them is used as a detection light , the probe light passes through the pinhole diaphragm 3 and a pair of gratings 4. Since the grating pair provides negative dispersion, the laser pulse is broadened into a negatively chirped pulse in time, and it also has the characteristic of spatial chirp, that is, each spectral component is in It is separated in space, as shown in Figure 2, the long-wavelength and short-wavelength components are separated; then after passing through the first polarizer 6, the first focusing lens 7 is focused on the nonlinear medium 8; another beam of laser pulse passes through as pump light The mirror M1 passes through the optical delay device composed of M2, M3, M4, and M5, and then the laser pulse passes through the half-wave plate 12 to adjust the polarization direction to rotate 45°, so that the angle between the polarization direction of the pump light and the detection light is 45°, Focusing on the nonlinear medium 8 by the second focusing lens 13, 45° is the best implementation mode, and the included angle between the polarization directions of the pump light and the probe light can also be any angle except 90°. The nonlinear medium is arranged at the junction of the outgoing light path of the first focusing lens and the outgoing light path of the second focusing lens, so that the detection light and the pumping light are spatially overlapped in the nonlinear medium 8; the optical delay device is adjusted so that the detection light and the pumping light are spatially overlapped in the nonlinear medium 8; The pump light coincides temporally in the nonlinear medium 8 . The probe light transmitted through the nonlinear medium is collimated by the collimator lens 9, and then received by the CCD 11 after passing through the second polarizer 10, and the transmission polarization directions of the second polarizer and the first polarizer are perpendicular to each other. the

The second scheme of the device of the present invention is shown in Fig. 3, the grating is replaced by a prism, and the laser pulse is broadened into a chirped pulse in time and space. the

The grating is a reflection grating or a transmission grating; the prism can be a triangular prism, especially various triangular prisms with dispersion properties. The nonlinear medium is a liquid or solid material with a large third-order nonlinear coefficient, preferably CS ₂ , bismuthate glass or tellurite glass. The polarizer is a polarizing prism or a polarizer or a half-wave plate. It is best to choose a polarizer with a high extinction ratio, because the higher the extinction ratio, the higher the final measurement accuracy. The polarizer is preferably a Nikkor prism, a Glan prism, a Glan-Taylor prism or a Wollaston prism, the extinction ratio of which can be higher than 10 ⁵ .

The measuring device also includes a spatial light modulator or an attenuating element arranged between the stretching device and the CCD. The spatial light modulator or the attenuating element is used to attenuate the portion with a strong detection signal intensity on the CCD by a fixed multiple to prevent the CCD from Saturation of the surface increases the dynamic range of the detectable signal-to-noise ratio. the

The time window for measuring the signal-to-noise ratio of this measuring device is determined by the time chirp of the probe light. The greater the dispersion obtained by the probe light passing through the grating pair or prism pair, the greater the chirp contained, that is, the wider the pulse spread , the final measurable time window is larger. It can usually be extended to the order of hundreds of picoseconds to nanoseconds. the

The time resolution of the device for measuring the signal-to-noise ratio is determined by the response time of the nonlinear medium and the spatial resolution of the CCD. The faster the response time of the nonlinear medium (such as bismuthate glass can reach the femtosecond level), the better the time resolution of the signal-to-noise ratio measurement; the higher the spatial resolution and the larger the lateral size of the CCD, the better the time resolution improvement. the

The dynamic range of the device for measuring signal-to-noise ratio depends on the extinction ratio of the first polarizer and the second polarizer and the dynamic range of the CCD. When the two polarizers are adjusted to be strictly perpendicular, the higher the extinction ratio of the two polarizers, the better, usually higher than 10 ⁵ ; at the same time, the larger the dynamic range of the CCD, the better, preferably a scientific grade CCD, which requires a large dynamic range. Such as 16 bits. In short, the higher the extinction ratio of the first polarizer and the second polarizer, the larger the dynamic range of the CCD, and the larger the dynamic range of the final measured signal-to-noise ratio.

Claims (6)

1. based on the single signal-to-noise ratio measurement apparatus of chirped pulse characteristic, comprise testing laser is divided into the beam splitting arrangement of pump light and detection light and will surveys the apparatus for widen that light carries out broadening, it is characterized in that: described apparatus for widen comprise the grating pair formed by two blocks of identical gratings or the prism formed by two identical prisms right, first block of grating in the described grating pair is arranged at the light path of surveying light, second block of grating is arranged on first grating diffration light path, and described prism is to the same manner setting; First polarizer is arranged on the emitting light path of second block of grating, and the pulse behind the broadening focuses in the nonlinear medium through first polarizer.

2. the single signal-to-noise ratio measurement apparatus based on the chirped pulse characteristic according to claim 1, it is characterized in that: described measurement mechanism also comprises spatial light modulator or the attenuating elements that is arranged between apparatus for widen and the CCD, described spatial light modulator or attenuating elements are used for detecting the fixedly multiple ground decay of strong signal on the CCD, it is saturated to prevent that CCD from practising physiognomy, and increases detectable dynamic range.

3. the single signal-to-noise ratio measurement apparatus based on the chirped pulse characteristic according to claim 2, it is characterized in that: described CCD selects scientific grade CCD for use.

4. the single signal-to-noise ratio measurement apparatus based on the chirped pulse characteristic according to claim 3, it is characterized in that: described first polarizer is polarizing prism or polaroid.

5. the single signal-to-noise ratio measurement apparatus based on the chirped pulse characteristic according to claim 4, it is characterized in that: described first polarizer is Nikkor prism, Glan prism, Glan-Taylor prism or wollaston prism.

6. the single signal-to-noise ratio measurement apparatus based on the chirped pulse characteristic according to claim 5, it is characterized in that: described nonlinear medium is CS ₂, bismuthate glass or tellurate glass.

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