CN1295561C - Ultrafast Pulse X-ray Phase Contrast Imaging Device - Google Patents

Abstract

An ultrafast pulse X-ray phase contrast imaging device is characterized by comprising a femtosecond laser system, a beam splitter, an optical delay line, a total reflector and a target chamber, wherein an achromatic lens, a sample chamber, a solid target and a concave reflector are arranged in the target chamber, a detector is arranged outside the target chamber, and the position relation of the components is as follows: the beam splitter is arranged on a laser output light path of the femtosecond titanium gem laser system, a laser beam output by the femtosecond titanium gem laser system is split into A, B two light beams by the beam splitter, wherein, a light beam enters a target chamber through an optical delay line and is converged by an achromatic lens to irradiate gas in a sample chamber, a light beam B enters the target chamber through a total reflector, is reflected by a concave reflector and is converged on a solid target to generate an X ray, the X ray enters the sample chamber, the state of plasma in the sample chamber is recorded by a detector, and the distance between the detector and the gas chamber meets the phase contrast imaging condition.

Description

Ultrafast Pulse X-ray Phase Contrast Imaging Device

Technical field:

The invention relates to an X-ray phase contrast imaging device, in particular to an ultrafast X-ray phase contrast imaging device. This imaging device has important application prospects in the study of the formation process of ultrashort pulse self-focusing filaments and the formation of ultrafast plasma.

Background technique:

In recent years, X-ray phase-contrast imaging technology has achieved rapid development. The biggest feature of this imaging technology is that it can obtain phase information without using interference method. It is also different from traditional Zernike phase-contrast interference microscopes, which do not require any optical components to change the phase of X-rays to obtain phase information.

When partially coherent X-rays pass through an object, in addition to absorption, a phase change occurs, that is, a distortion of the wavefront occurs. This wavefront distortion causes the propagation direction of part of the wavefront to change, and it will overlap with the undistorted wavefront to form interference. In this way, the phase changes are converted into intensity changes, and the phase change images can be obtained directly without any reconstruction techniques.

X-ray phase-contrast imaging technology has been widely used in the study of living organisms, material analysis and many other fields, and has achieved many fruitful results. Unfortunately, the X-ray sources used in X-ray phase-contrast imaging are limited to synchrotron radiation sources and X-ray tubes. Therefore, the exposure time is as long as several seconds or even tens of minutes, and the research objects are all static samples. The further development of X-ray phase contrast imaging technology is limited.

Invention content:

The present invention proposes an ultrafast pulse X-ray phase-contrast imaging device aimed at the above-mentioned shortcomings in the prior art, which can be used to study ultrafast physical processes.

At the end of the last century, with the appearance of femtosecond laser pulses, many new phenomena, new laws, new mechanisms and new methods began to be revealed one by one. At the same time, some new fields are constantly being explored, and femtosecond pulse imaging technology is one of the new fields that is very eye-catching.

Many events that occur on atoms and molecules have time scales in the order of picoseconds and femtoseconds. During chemical reactions, the breaking and recombination of molecular bonds and the collision of molecules in liquids are ultrafast processes that occur on the femtosecond scale. The photo-electric effect or light-light interaction in semiconductor processing, the self-focusing phenomenon generated by femtosecond pulses, etc. are all ultrafast processes, which is why we are so interested in it.

To measure a process generally needs to be measured with a process shorter than this time. In the past two decades, the pulse width of ultrashort pulses has been compressed from picoseconds to femtoseconds. Although the generation of sub-femtosecond pulses has been reported under experimental conditions, it has not yet entered the practical stage. Therefore, femtosecond laser pulses are currently an important means of detecting ultrafast processes. Live detection, medical surgery and the manufacture of ultra-small satellites all have their unique advantages and irreplaceable roles. Applying femtosecond pulsed laser to imaging is a promising technology, which has shown its superiority in many detection fields. The coherence length of the femtosecond pulsed laser is short, and it is very difficult to take a high-resolution hologram on the femtosecond time scale. For example, if a 100fs pulse is used to record, the number of fringes contained in the hologram will be less than 100, which seriously reduces the resolution. rate and field of view of the hologram. However, if femtosecond pulses interact with solid materials to generate X-rays, it will be an excellent X-ray source, thereby overcoming the shortcomings of femtosecond pulse broadband.

Technical solution of the present invention is as follows:

An ultrafast pulsed X-ray phase-contrast imaging device, its composition includes: a femtosecond laser system, a beam splitter, an optical delay line, a total reflection mirror and a target chamber, the target chamber is equipped with an achromatic lens, a sample chamber, a solid target and a concave reflector, there is also a detector outside the target chamber, and the positional relationship of the above-mentioned components is as follows: the beam splitter is set on the laser output optical path of the femtosecond Ti:sapphire laser system, and the femtosecond The laser beam output by the titanium sapphire laser system is divided into two beams, A and B. The A beam enters the target chamber through the optical delay line, and is converged by the achromatic lens to irradiate the gas in the sample chamber. The B beam is reflected by the total reflection mirror and enters the target chamber. The concave mirror reflects and focuses on the solid target, generating an X-ray, which enters the sample chamber where the state of the plasma is recorded by a detector. The distance between the detector and the gas chamber satisfies the phase contrast imaging conditions:

${\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 0.49</span>}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 0.49</span>}}$

The said femtosecond Ti:Sapphire laser system is a desktop device with a radiation wavelength of 780-820nm, a pulse width of 100fs, and an output energy of 100nj.

The so-called beam splitter is actually a semi-reflective and semi-transmissive dielectric film, which is a dielectric film with 50% reflection and 50% transmission. It divides the incident femtosecond Ti:Sapphire laser pulse into A beam and B beam. beam.

The so-called total reflection dielectric diaphragm is a 100% total reflection dielectric diaphragm, wherein three total reflection dielectric diaphragms form an optical delay line to adjust the relative optical delay between the A beam and the B beam.

The solid target is a movable solid target. When the femtosecond titanium sapphire laser pulse interacts with it, characteristic X-ray K _α1 and K _α2 lines will be generated, and the corresponding radiation wavelength is 0.5-1.8 Ȧ.

The so-called achromatic lens is a lens used to focus the femtosecond Ti:Sapphire laser, and the plasma generated by irradiating the gas in the air chamber is used as the measured sample.

The so-called air chamber is used to store the gas that generates plasma. When the femtosecond Ti:Sapphire laser interacts with it, plasma will be generated. The whole process of the plasma generation, expansion, and disappearance will be used as the research object.

The so-called concave mirror is an aspherical concave mirror, which is used to focus the femtosecond Ti:Sapphire laser and irradiate the solid target to generate X-rays.

Said X-ray detector is a CCD camera in the X-ray band.

Technical effect of the present invention is as follows:

The invention adopts femtosecond laser to interact with a solid target to generate laser plasma X-rays as a detection beam. The size of the X-ray source depends on the size of the focused spot of the concave mirror, usually the size of the focal spot is 10-20 μm, which is nearly an order of magnitude smaller than the size of the synchrotron radiation source, thus ensuring that the X-ray symmetrical imaging resolution can reach 10- 20μm size.

The pulse duration of laser plasma X-rays is shorter than that of laser pulses, thereby ensuring that the time resolution of the present invention is better than 100 fs. Due to the use of time delay lines, the relative delay between the active beam and the detection beam can be easily adjusted. When the active beam generates plasma as the research object in the sample chamber, the detection beam has to enter the sample to be tested with different time delays, and the whole process of the plasma to be studied can be recorded.

Compared with the prior art, the present invention adopts the plasma X-ray source generated by femtosecond pulsed laser, the pulse time is about 100fs, and can be regarded as a point light source, so the spatial equality is quite good, and can be used to study high-speed dynamic Events, the spatial resolution can reach 10-20μm, and the time resolution can reach about 100fs.

Description of drawings:

Fig. 1 is a principle diagram of the ultrafast pulsed X-ray phase-contrast imaging device of the present invention.

Detailed ways:

The ultrafast pulsed X-ray phase contrast imaging device of the present invention is shown in FIG. 1 . It includes a femtosecond laser system 1, a beam splitter 2, an optical delay line composed of total reflection mirrors 3, 4, 5, a total reflection mirror 6 and a target chamber 12, which is equipped with a Chromatic aberration lens 8 , a sample chamber 9 , a solid target 7 and a concave mirror 10 , and a detector 11 outside the target chamber 12 . The positional relationship of the above components is as follows: a beam splitter 2 is placed on the laser output optical path of the femtosecond Ti:sapphire laser system 1, and the laser output from the femtosecond Ti:sapphire laser system 1 outputs two beams A and B through the beam splitter 2. The light beam A enters the target chamber 12 through the optical delay line, is converged by an achromatic lens 8 and enters the sample chamber 9 and interacts with the gas therein to generate a plasma to be studied. Such beams are called action beams.

The light beam B is reflected by a total reflection mirror 6 and enters the target chamber 12 . It is reflected by a concave mirror 10 and converged onto the solid target 7 to generate an X-ray which then enters the sample chamber 9 to detect the process of plasma generation by the A beam. The B beam is called the probe beam.

The state of the plasma in the sample chamber is recorded by a detector. The distance between the detector and the gas chamber satisfies the phase contrast imaging conditions:

${\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 0.49</span>}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 0.49</span>}}$

The femtosecond Ti:Sapphire laser system 1 is a desktop device with a radiation wavelength of 780-820nm, a pulse width of 100fs, and an output energy of 100nj.

The said beam splitter 2 is actually a semi-reflective and semi-permeable dielectric membrane, which is a dielectric membrane that reflects 50% of 800nm and transmits 50%. It divides the incident femtosecond Ti:Sapphire laser pulse into A beam and B beams.

Said total reflection dielectric diaphragms 3, 4, 5, 6 are dielectric diaphragms for 800nm100% total reflection one by one, wherein the total reflection dielectric diaphragms 3, 4, 5 form an optical delay line for adjusting A The relative optical delay between the B beam and the B beam.

The solid target 7 is a movable copper target. When the femtosecond titanium sapphire laser pulse interacts with it, characteristic X-ray K _α1 and K _α2 lines will be generated, and the corresponding radiation wavelengths are 1.540562 Ȧ and 1.544398 Ȧ.

The achromatic lens 8 is used to focus the femtosecond Ti:Sapphire laser to irradiate the gas in the sample chamber 9 to generate plasma and form the sample to be measured.

The said air chamber 9 is used to store the gas that generates the plasma. When the femtosecond Ti:Sapphire laser interacts with it, the plasma will be generated. The whole process of the generation, expansion and disappearance of the plasma will be used as the research object.

Said concave reflector 10 is an aspheric concave mirror, which is used for focusing as a target lens.

Said X-ray detector 11 is a CCD camera in the X-ray band.

The working principle and basic process of the ultrafast X-ray phase contrast imaging device of the present invention are:

When hard X-rays penetrate the sample, if the detector is placed directly behind the sample, an X-ray projection image based on the absorption contrast mechanism is recorded. If the distance between the detector and the sample satisfies the following formula:

${\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 0.49</span>}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 0.49</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

The phase contrast image of the object can be obtained, where: λ is the wavelength of the X-ray, U is the spatial frequency of the object, and Z ₁ is the distance between the sample to be measured and the X-ray source. Therefore, when λ, U, and _Z1 have been determined, _Z2 has a certain distance. In particular, it should be pointed out that this phase contrast imaging reflects the places where the refractive index of the object changes suddenly.

The vacuum target chamber 12 adopts 3 mechanical pumps and 3 diffusion pumps, which can make the vacuum degree in the vacuum chamber reach 5×10 ⁻⁸ τ.

When the femtosecond Ti:Sapphire laser pulse is incident on the semi-reflective and semi-permeable dielectric membrane plate 2, it is divided into A beam and B beam. The femtosecond pulse of beam A enters the vacuum target chamber 12 after passing through the delay line formed by the fully reflective dielectric film plates 3, 4, 5, and is focused by the achromatic lens 8 into the gas chamber 9 to generate plasma.

The femtosecond pulse of the B beam is reflected by the total reflection mirror 6 and enters the vacuum chamber 12. It is focused by the concave mirror 10 and incident on the solid copper target 7 to generate the characteristic X-ray K _α1 line and K _α2 line of copper. This X-ray is used as the gas chamber 9 The plasma X-ray source, since the distance between the detector 11 and the gas chamber 9 satisfies the phase contrast imaging condition of formula 1, the change of the plasma refractive index in the gas chamber can be measured, and the delay line can be changed to measure the change of the plasma in the gas chamber from process from birth to disappearance.

Claims (8)

1. An ultrafast pulsed X-ray phase-contrast imaging device, characterized in that its composition includes a femtosecond Ti:Sapphire laser system (1), a beam splitter (2), an optical delay line, a total reflection mirror (6) and a target Chamber (12), this target chamber (12) is provided with achromatic lens (8), sample chamber (9), solid target (7) and concave mirror (10), outside this target chamber (12) also has A detector (11), the positional relationship of the above-mentioned components is as follows: the beam splitter (2) is set on the laser output optical path of the femtosecond Ti:sapphire laser system (1), and the beam splitter (2) will fly The laser beam output by the second Ti:Sapphire laser system (1) is divided into two beams, A and B. The beam A enters the target chamber (12) through the optical delay line, and is converged by the achromatic lens (8) to irradiate the gas in the sample chamber (9). , the B light beam is reflected by a total reflection mirror (6) and enters the target chamber (12), is reflected by the concave mirror (10) and converges on the solid target (7), and generates an X-ray, which enters the sample chamber (9 ), the state of the plasma in the sample chamber (9) is recorded by the detector (11), and the distance Z between the detector (11) and the sample chamber ( ₉ ) satisfies the following phase contrast imaging conditions: ${\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 0.49</span>}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}{\mathrm{<span\; class="notranslate">\; u</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 0.49</span>}}$ In the formula: λ is the wavelength of X-rays, U is the spatial frequency of the object, and Z ₁ is the distance between the sample to be measured and the X-ray source. 2. The ultrafast pulsed X-ray phase contrast imaging device according to claim 1, characterized in that the femtosecond Ti:sapphire laser system (1) has a radiation wavelength range of 780-820nm and a pulse width of 5-100fs, Benchtop device with output energy from 10nJ-1000nJ. 3. The ultrafast pulsed X-ray phase contrast imaging device according to claim 1, characterized in that the beam splitter (2) is a dielectric film with 50% reflection and 50% transmission. 4. The ultrafast pulsed X-ray phase-contrast imaging device according to claim 1, characterized in that the optical delay line is composed of a 100% fully reflective dielectric film plate (3, 4, 5). 5. The ultrafast pulsed X-ray phase contrast imaging device according to claim 1, characterized in that the solid target (7) is a movable solid target, when the femtosecond Ti:sapphire laser pulse interacts with it , will produce characteristic X-ray K _α1 and K _α2 lines, the corresponding radiation wavelength is 0.5-1.8 Ȧ. 6. The ultrafast pulse X-ray phase contrast imaging device according to claim 1, characterized in that the achromatic lens (8) is a lens for focusing femtosecond Ti:Sapphire laser light. 7. The ultrafast pulse X-ray phase contrast imaging device according to claim 1, characterized in that the concave mirror (10) is an aspherical concave mirror. 8. The ultrafast pulsed X-ray phase contrast imaging device according to claim 1, characterized in that the detector (11) is a CCD camera in the X-ray band.