KR100926032B1 - Time-resolved terahertz pump-probe spectrometer - Google Patents

Abstract

The present invention relates to a time-resolved THz pump-probe spectrometer, and in particular, two femtosecond laser beams are separated, and two beams are incident on a sample through a THz probe and a THz pump to generate THz waves, and a THz pump beam and a THz probe. By varying the time difference at which the beam reaches the sample, the THz probe beam is changed according to the time difference, and the THz probe beam and the third beam that have passed through the sample can be collected to detect terahertz waves. A time-resolved THz pump-probe spectrometer capable of measuring the amount of change in terahertz waves over time in the hertz frequency domain. The present invention for achieving this object, the beam generator 10 for generating a femtosecond ultra-fast laser beam; First and second beam separators 20 and 30 for separating the femtosecond ultrafast laser beam into first, second and third beams; A THz probe 40 generating a terahertz wave by using the first beam and incident the sample 100 into the sample 100; A THz pump 50 which generates a terahertz wave using the second beam and enters the sample 100 to vary the frequency of the terahertz wave; And measuring means 60 for condensing the terahertz probe beam and the third beam that have passed through the sample 100 and measuring the terahertz wave.

Titanium-Sapphire Laser Beam, THz Probe, THz Pump, Transmitter Delay, Detector

Description

Time-resolved terahertz pump-probe spectrometer

The present invention relates to a time resolved THz pump-probe spectrometer, and to provide a THz pump-probe spectrometer superior to conventional time resolved femtosecond laser pump-THz probe spectroscopy.

In general, the terahertz (THz) wave has been a frequency band that has not been reached for a long time at the boundary between the radio wave and the light wave. It is a field that is being pioneered as a new field for industrial use such as identification of materials and biometrics.

These THz waves have been researched and used in radio astronomy and analytical science in a limited manner, but they are expected to be applied to various fields such as industrial, medical, bio, agricultural, and safety in recent years.

In addition, in recent years, it has become possible to develop ultra-high speed signal processing technology and devices using THz waves, and thus, 1) photonics field using THz electromagnetic waves, 2) THz electronic engineering field, and 3) THz waves in the THz wave band. It is roughly classified into the field of imaging and is increasingly used in each field.

In the field of optical engineering, photo-mixing has enabled the development of wireless communication technology in the 120 GHz band, which enables the transfer of information of several tens of Gbps, and the development of semiconductor quantum well structures that are highly precisely controlled with the development of nanotechnology. The low frequency of 1.9THz band is progressing.

In the field of electronics, the development of integrated circuits (MMICs) or high-speed AD converters using compound semiconductors is also underway. In addition, the development of a superconducting single magnetic flux quantum (SFQ) logic circuit enables the shift registers operating in the 120 GHz band and the optical pocket switch of 160 Gbps to be used for THz digital signal processing technology, which is widely used in wireless and measurement applications. have.

In the field of using THz electromagnetic waves, in particular, the development of the time domain spectroscopy of THz waves with the development of femto-second lasers, the generation of ultra-wideband microwave pulses over tens of GHz to 100 THz and measurement of the time domain New THz spectroscopy and imaging techniques are being developed.

However, conventional THz spectroscopy and projection techniques have a problem that the amount of change in terahertz waves in the THz region cannot be measured properly.

According to the present invention, the femtosecond laser beam is separated into three, and the two beams are incident on the sample through the THz probe and the THz pump to generate the THz wave, and by varying the time difference between the THz pump beam and the THz probe beam reaching the sample. By changing the THz probe beam according to the time difference and concentrating the THz probe beam and the third beam passing through the sample, the terahertz wave can be detected. A time resolved THz pump-probe spectrometer capable of measuring the amount of change.

The present invention for achieving this object,

A beam generator 10 for generating a femtosecond ultrafast laser beam;

First and second beam separators 20 and 30 for separating the femtosecond ultrafast laser beam into first, second and third beams;

A THz probe 40 generating a terahertz wave by using the first beam and incident the sample 100 into the sample 100;

A THz pump 50 which generates a terahertz wave using the second beam and enters the sample 100 to vary the frequency of the terahertz wave; And

And measuring means (60) for measuring the terahertz wave by condensing the terahertz probe beam and the third beam transmitted through the sample (100).

In addition, the beam generator is a beam generator for generating a femtosecond ultrafast laser beam, characterized in that the beam generated in the beam generator is a beam having a pulse width of 10 ~ 100fs and a repetition rate of 10MHz.

In addition, the second and third beams respectively pass through the light transmission delays 31 and 21 and are incident on the THz pump 50 and the measuring means 60, respectively.

In addition, the first beam splitter 20 is characterized in that the reflected light of the ultra-fast laser beam is incident on the THz probe 40.

In addition, the second beam separator 30 is characterized in that the incident second beam is incident on the THz pump 50 and the reflected third beam is incident on the measuring means 60.

In addition, the THz probe 40 and the THz pump 50 each include a condenser lens 41 and 51, a ZnTe crystal 42 and 52 for generating THz, and axle mirrors 43 and 53 for beam amplification. It features.

In addition, the measuring means 60 collects the non-axis mirror 63 for condensing the third beam, the THz-generating ZnTe crystal 62 for generating the terahertz wave, and the third beam for changing the linear polarization. A light collecting lens 61, a polarizing plate 64 for polarizing the third beam, a beam splitting polarizer 65 for separating the focused beam, and a detector 66 for detecting each split beam. It is characterized by.

In addition, the polarizing plate 64 polarizes the third beam circularly, and is characterized by being a λ / 4 polarizing plate.

According to the present invention, the conventional time resolution laser beam pump-THz probe spectrometer uses several hundred times higher energy than the energy in the THz region as a pump, while the reliability of time resolution spectroscopy in the THz region is low, whereas the THz pump-probe spectrometer is low. Since is used as the pump beam in the energy of the THz region, there is an effect that can obtain a high measurement reliability.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

1 is a schematic diagram showing the construction of a time resolved THz pump-probe spectrometer according to the present invention.

The present invention includes a beam generator 10 for generating a femtosecond ultrafast laser beam, and two first and second beam splitters 20 and 30 for spectroscopically analyzing the ultrafast laser beam into three. In addition, the present invention includes a THz probe 40 and a THz pump 50 for concentrating two spectroscopic laser beams to generate terahertz (THz), and a measuring means 60 for measuring terahertz. .

The beam generator 10 uses a femtosecond titanium-sapphire ultrafast laser beam that can generate ultra-wideband microwave pulses and measure time domains. In particular, in a preferred embodiment of the present invention, it is preferable to use the ultrafast laser beam having a pulse width of 10 to 100fs to maximize the THz generation intensity and the wide THz frequency range.

The first and second beam separators 20 and 30 may be manufactured by conventional techniques. At this time, the first beam splitter 20 partially reflects the laser beam incident from the beam generator 10 to form a first beam, and transmits the remaining beam to form a second beam. In addition, the second beam splitter 30 partially transmits the incident second beam to form a second beam and reflects the rest to generate a third beam.

In a preferred embodiment of the present invention, the femtoseconds are constructed by allowing the second and third beams to pass through each of the light transmission delays 21 and 31 before being incident on the THz pump 50 and the measuring means 60, respectively. It is preferable to configure so that time resolution of can be performed.

The THz pump 50 collects the second beam to generate terahertz waves, and scans the generated terahertz waves into the sample 100. The THz pump 50 includes a condenser lens 51 and a ZnTe crystal 52 for wavelength generation for obtaining a light source of a suitable wavelength. Here, the thinner the ZnTe crystal, the smaller the magnitude of the signal of the terahertz wave and the wider spectrum can be obtained.

In particular, it is preferable that the THz pump 50 includes off-axis mirrors 53 for amplifying the generated terahertz waves. Here, the non-axis mirror condenses the beams so that the beam paths are all the same.

The terahertz wave generated as described above is projected onto the sample 100 to be extinguished by the block 110.

The THz probe 40 has the same configuration as the THz pump 50, a condensing lens 41 for condensing the first beam, a ZnTe crystal 42 for obtaining terahertz waves of an appropriate wavelength, and the terahertz waves. It includes a stock mirror 43 for amplifying the. Since these components have the same function as those of the above-described THz probe 40, the description thereof is omitted here.

Thus, the terahertz wave generated by the THz probe 40 is injected into the sample 100 and its intensity is changed by the time difference reached from the terahertz wave incident from the THz pump 50 and passes through the sample 100. One changed terahertz light source is detected by the measuring means 60.

The measuring means 60, like the THz pump 50 and the THz probe 40 described above, is a condenser lens 61 for condensing the third beam, and ZnTe, which is a medium for interacting the terahertz wave and the third beam. It comprises a crystal 62, and a storage mirror 63 for condensing the terahertz wave and the third beam.

These components have the same function as the components of the THz probe 40 and the THz pump 50 described above, but differ in their arrangement. That is, the measuring means 60 transmits the terahertz wave and the third beam, which are transmitted through the sample 100 and collected by the non-mirror mirror 63, together with the third beam through the ZnTe crystal 62, and at an arbitrary angle by light rectification. The third beam of the linearly polarized light is condensed by the condensing lens 61.

 In a preferred embodiment of the present invention, the measuring means 60 changes the circular or elliptical polarization by transmitting the third beam whose linear polarization is changed by the terahertz wave scanned from the THz probe 40 to the polarizing plate 64. It is desirable to be able to obtain the effect of making it. Here, it is more preferable that the polarizing plate 64 uses a λ / 4 polarizing plate, and λ means a wavelength.

In addition, the measuring means 60 further includes a beam splitting polarizer 65 to separate the light sources collected through the light collecting lens 63 according to the polarization, respectively, a detector for detecting the separated light sources (balanced detecter, 66) It is preferable to include).

According to the present invention including the configuration thus made, it is possible to control the difference between the time when the THz probe beam reaches the sample 100 and the time when the THz pump beam reaches the sample 100. Therefore, the amount of absorption of the sample 100 changed by the THz pump beam can be measured with time.

Although the present invention has been described in connection with the above-mentioned preferred embodiments, it is possible to make various modifications or variations without departing from the spirit and scope of the invention. Accordingly, the appended claims will cover such modifications and variations as fall within the spirit of the invention.

1 is a schematic view showing the construction of a time resolved THz pump-probe spectrometer according to the present invention;

<Explanation of symbols for the main parts of the drawings>

10: beam generator

20: first beam separator

21, 31: photoelectric relay

30: second beam separator

40: THz probe

41, 51, 61: condensing lens

42, 52, 62: ZnTe crystal

43, 53, 63: Stock Mirror

50: THz Pump

60 measuring means

64: polarizer

65: beam splitting polarizer

66: detector

100: sample

110: block

Claims (10)

A beam generator 10 generating a femtosecond ultrafast laser beam having a pulse width of 10 to 100 fs and a repetition rate of 10 MHz; First and second beam splitters 20 and 30 for separating the femtosecond ultrafast laser beam into first, second and third beams; THz including a condenser lens 41 for generating a terahertz wave using the separated first beam and incident on the sample 100, a ZnTe crystal 42 for generating THz, and a non-axis mirror 43 for beam amplification. Probe 40; A terahertz wave is generated using the separated second beam and is incident on the sample 100 to condense the lens 51 for varying the frequency of the terahertz wave, the ZnTe crystal 52 for THz generation, and beam amplification. A THz pump (50) having a stockpile mirror (53); And It comprises a measuring means 60 for measuring the terahertz wave by collecting the terahertz probe beam and the third beam transmitted through the sample 100, the second beam splitter 30 is the second transmitted The beam is incident on the THz pump 50 through the light transmission delay 31, and the reflected third beam is incident on the measuring means 60 through the light transmission delay 21. THz pump-probe spectrometer. delete delete delete delete delete delete The method of claim 1, The measuring means 60 includes a stock mirror 63 for condensing the third beam, ZnTe crystal (62) for THz generation which produces terahertz waves, A condenser lens 61 for condensing the third beam having the linearly polarized light; A polarizing plate 64 for polarizing the third beam, And a detector (66) for detecting each beam separated by a beam splitting polarizer (65) for separating the condensed beams. The method of claim 8, The polarizing plate (64) is a time-resolved THz pump-probe spectrometer, characterized in that for circularly polarizing the third beam. The method of claim 9, The polarizing plate (64) is a λ / 4 polarizing plate, characterized in that the THz pump-probe spectrometer.

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