Method and apparatus for creating a microscopic sample image of a molecular vibrational response of a sample

A microscopic imaging method for creating a microscopic sample image of a sample to be investigated, comprising the steps of

• arranging the sample on a sampling crystal,
• irradiating the sample with excitation laser pulses and generating sample response pulses with a sample response field as a result of an interaction of the excitation laser pulses with the sample,
• irradiating the sampling crystal with probe laser pulses being temporally synchronized with the excitation laser pulses and spatially overlapped with the sample response pulses in the sampling crystal, wherein the probe laser pulses have a shorter wavelength than the excitation laser pulses,
• detecting the sample response field by electric-field sampling with the sampling crystal, using the sample response pulses and the probe laser pulses, and
• calculating the sample image based on the detected sample response field, wherein
• the excitation laser pulses have a wavelength in a range from mid-infrared to visible light and the sample response pulses are created by a coherent interaction process induced in the sample and with a fixed phase relationship relative to the excitation laser pulses,
• the sampling crystal is a non-centrosymmetric crystal,
• the irradiating step is repeated at multiple sample points, where the sample and the probe laser pulses are focused to the sampling crystal, wherein at each sample point,
• the irradiating steps are successively repeated with multiple temporal probe delays of the probe laser pulses relative to the excitation laser pulses,
• at each probe delay, a sum or difference frequency pulse of a current sample response pulse and a current probe laser pulse is generated, and
• at each probe delay, a spectral interference pulse is created by a spectral interference of the sum or difference frequency pulse and the current probe laser pulse,
• the detecting step includes sensing a polarization state of the spectral interference pulse by an ellipsometer device at each probe delay, wherein the local sample response field at the sample point is derived from polarization states sensed at all probe delays, the sample image is calculated based on the sample response field detected at the sample points and
• a dispersion setting is provided such that the probe laser pulses have maximum frequency compression in the sampling crystal.

A microscopic imaging method for creating a microscopic sample image of a sample to be investigated, comprising the steps of

• arranging the sample on a sampling crystal
• irradiating the sample with excitation laser pulses and generating sample response pulses with a sample response field as a result of an interaction of the excitation laser pulses with the sample, irradiating the sampling crystal with probe laser pulses being temporally synchronized with the excitation laser pulses and spatially overlapped with the sample response pulses in the sampling crystal, wherein the probe laser pulses have a shorter wavelength than the excitation laser pulses,
• detecting the sample response field by electric-field sampling with the sampling crystal, using the sample response pulses and the probe laser pulses, and
• calculating the sample image based on the detected sample response field, wherein,
• the excitation laser pulses have a wavelength in a range from mid-infrared to visible light and the sample response pulses are created by a coherent interaction process induced in the sample and with a fixed phase relationship relative to the excitation laser pulses,
• the sampling crystal is a non-centrosymmetric crystal,
• the irradiating step is repeated at multiple sample points, where the sample and the probe laser pulses are focused to the sampling crystal, wherein at each sample point
• the irradiating steps are successively repeated with multiple temporal probe delays of the probe laser pulses relative to the excitation laser pulses,
• at each probe delay, a sum or difference frequency pulse of a current sample response pulse and a current probe laser pulse is generated, and
• at each probe delay, a spectral interference pulse is created by a spectral interference of the sum or difference frequency pulse and the current probe laser pulse,
• the detecting step includes sensing a polarization state of the spectral interference pulse by an ellipsometer device at each probe delay, wherein the local sample response field at the sample point is derived from polarization states sensed at all probe delays,
• the sample image is calculated based on the sample response field detected at the sample points, and
• the multiple spectral interference pulses are created by a spectral interference of a higher harmonic of the sample response pulses and higher harmonics of the probe laser pulses in the sampling crystal.

A microscopic imaging apparatus, being configured for creating a microscopic sample image of a sample to be investigated, comprising

• a sampling crystal being arranged for accommodating the sample,
• an excitation laser source being configured for irradiating the sample through imaging optics with excitation laser pulses, so that sample response pulses with a sample response field can be generated as a result of an interaction of the excitation laser pulses with the sample,
• a probe laser source being configured for irradiating the sampling crystal through the imaging optics with probe laser pulses and being temporally synchronized with the excitation laser source, so that the probe laser pulses can be spatially overlapped with the sample response pulses in the sampling crystal, wherein the probe laser source is configured for creating the probe laser pulses with a wavelength shorter than the excitation laser pulses,
• an ellipsometer device being configured for detecting the sample response field by electric-field sampling with the sampling crystal, using the sample response pulses and the probe laser pulses,
• a computer device being configured for calculating the sample image based on the detected sample response field, and
• a control device being configured for controlling the excitation laser source, the probe laser source and the ellipsometer device, wherein
• the excitation laser source is configured for creating the excitation laser pulses in a wavelength range from mid-infrared to visible light and for irradiating the sample with the excitation laser pulses such that the sample response pulses can be created by a coherent interaction process induced in the sample and with a fixed phase relationship relative to the excitation laser pulses,
• the sampling crystal is a non-centrosymmetric crystal,
• the imaging optics are configured for focused irradiation of the sample and the sampling crystal,
• a delay device is arranged for irradiating the sampling crystal with the probe laser pulses with an adjustable delay relative to the excitation laser pulses,
• the control device is configured for repeating the irradiating steps by a scanning device at multiple sample points, such that at each sample point
• the irradiating steps are successively repeated with multiple temporal probe delays of the probe laser pulses relative to the excitation laser pulses,
• at each probe delay, a sum or difference frequency pulse of a current sample response pulse and a current probe laser pulse is generated, and
• at each probe delay, a spectral interference pulse is created by a spectral interference of the sum or difference frequency pulse and the current probe laser pulse,
• the ellipsometer device is arranged for sensing a polarization state of the spectral interference pulse at each probe delay, wherein the local sample response field at the sample point can be derived from the polarization states sensed at all probe delays, and
• the computer device is configured for calculating the sample image based on the sample response field detected at the sample points, and
• the excitation laser source is configured for creating the excitation laser pulses comprising pump pulses and Stokes pulses and the coherent interaction process comprises stimulated Raman scattering, induced in the sample by the pump and Stokes pulses, wherein the sample response pulses are intensity changed Stokes pulses resulting from the stimulated Raman scattering, wherein the control device is configured such that at each sample point
• sum or difference frequency pulses are created by phase-matched, second order nonlinear interaction between the sample and probe laser pulses, and
• the spectral interference pulses are created by superimposing the sum or difference frequency pulses with the probe laser pulses.

A microscopic imaging apparatus, being configured for creating a microscopic sample image of a sample to be investigated, comprising

• a sampling crystal being arranged for accommodating the sample,
• an excitation laser source being configured for irradiating the sample through imaging optics with excitation laser pulses, so that sample response pulses with a sample response field can be generated as a result of an interaction of the excitation laser pulses with the sample,
• a probe laser source being configured for irradiating the sampling crystal through the imaging optics with probe laser pulses and being temporally synchronized with the excitation laser source, so that the probe laser pulses can be spatially overlapped with the sample response pulses in the sampling crystal, wherein the probe laser source is configured for creating the probe laser pulses with a wavelength shorter than the excitation laser pulses,
• an ellipsometer device being configured for detecting the sample response field by electric-field sampling with the sampling crystal, using the sample response pulses and the probe laser pulses,
• a computer device being configured for calculating the sample image based on the detected sample response field, and
• a control device being configured for controlling the excitation laser source, the probe laser source and the ellipsometer device, wherein
• the excitation laser source is configured for creating the excitation laser pulses in a wavelength range from mid-infrared to visible light and for irradiating the sample with the excitation laser pulses such that the sample response pulses can be created by a coherent interaction process induced in the sample and with a fixed phase relationship relative to the excitation laser pulses,
• the sampling crystal is a non-centrosymmetric crystal
• the imaging optics are configured for focused irradiation of the sample and the sampling crystal,
• a delay device is arranged for irradiating the sampling crystal with the probe laser pulses with an adjustable delay relative to the excitation laser pulses,
• the control device is configured for repeating the irradiating steps by a scanning device at multiple sample points, such that at each sample point
• the irradiating steps are successively repeated with multiple temporal probe delays of the probe laser pulses relative to the excitation laser pulses
• at each probe delay, a sum or difference frequency pulse of a current sample response pulse and a current probe laser pulse is generated, and
• at each probe delay, a spectral interference pulse is created by a spectral interference of the sum or difference frequency pulse and the current probe laser pulse,
• the ellipsometer device is arranged for sensing a polarization state of the spectral interference pulse at each probe delay, wherein the local sample response field at the sample point can be derived from the polarization states sensed at all probe delays,
• the computer device is configured for calculating the sample image based on the sample response field detected at the sample points, and
• at least one dispersion setting component is provided such that the probe laser pulses have maximum frequency compression in the sampling crystal.