Patent ID: 12247922

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The apparatus101as shown inFIG.1can be used for carrying out Raman spectroscopy, such as time-gated Raman spectroscopy, on a sample103, which is not part of the apparatus101. The apparatus101comprises an optoelectronic laser105for providing excitation radiation to the sample103. The sample103can be arranged, for example by a user of the apparatus, such that it can be exposed to the excitation radiation, which usually consists of or comprises laser light.

The apparatus101further comprises a transistor107, for example a Gallium Nitride field effect transistor, for modulating an electric current, which flows during operation of the apparatus101through the optoelectronic laser105and which causes the generation of the excitation radiation.

At least some embodiments of the apparatus101can be incorporated into a handheld electronic device, such as a cell phone, a smartphone or a tablet computer. For example, the handheld electronic device201ofFIG.2comprises such an apparatus having an optoelectronic laser203, for example a DFB or DBR laser diode, for providing excitation radiation207to sample205, which is arranged outside a housing209of the handheld electronic device201.

The excitation radiation207can have an average power of more than 100 mW. The excitation radiation can comprise green laser light, and the excitation radiation can include one or more wavelengths. For example, two wavelengths, one in the visible and one in the infrared, can help to obtain a better confirmation of the Raman signal.

The apparatus201also comprises a transistor211, such as a GaN FET, for modulating an electric current, which can flow through the optoelectronic laser203to cause the generation of the excitation radiation207.

The apparatus201also includes an objective213, for example in form of a focusing lens system which can comprise a plano convex lens. The objective213can focus the excitation radiation207to a spot215outside the housing209. The sample207is placed such that the spot215is located on the surface of the sample205. The objective213also serves to collect light scattered from the sample205. The scattered light includes Raman scattered light with wavelengths that are different from the wavelengths of the excitation radiation207.

A high pass filter217is configured to reflect the excitation radiation207from the optoelectronic laser203and to guide the excitation radiation207to the objective213. The high pass filter217is furthermore transparent for light with wavelengths, which are longer than the wavelengths of the excitation radiation207. Thus, the red shifted portion of the Raman scattered light can pass the high pass filter217and it can be focused through a slit219of a spectrometer221.

The spectrometer221comprises a diffraction element223, such as a diffraction grating, a photonic crystal, or a plasmonic Fabry Perot filter, which spatially splits the Raman light into its spectral components. A focusing lens system (not shown) images the spectral components on an array detector, such as a CCD array detector (CCD=charged coupled device).

The diagram15as shown inFIG.3illustrates a time-gated Raman spectroscopy process. The diagram15is also related to the setup ofFIG.5, which will be described further below in more detail.

As illustrated in301ofFIG.3, an optoelectronic laser is operated such as to provide laser pulses. The laser can be a low power (for example with an average power of 100 mW) DFB or DBR laser diode. A laser diode9is shown inFIG.5.

Alternatively, a VCSEL and a green laser, such as a direct transition green laser, could be used to provide laser light. The VCSEL can for example be configured to emit light in the infrared.

A control signal (frame sync signal)11is generated in303, which is used for controlling the operation of the laser9. The signal11can also trigger the flashing of a detector array, for example, a linear array, from existing charges according to305.

Regarding the generated laser pulse, it is reflected off the filter2(seeFIG.5) according to307. In309, the pulse travels through objective1and hits sample215(see also FIG.5). Light which includes Raman light is back scattered and collected by the objective1according to311ofFIG.3. The red-shifted Raman light passes the high pass filter2, and lens3focuses the light through slit4into the spectrometer according to313ofFIG.3.

The Raman light further passes through collimation and aberration correction optics5and diffracting element6which spatially splits the Raman light into its spectral lines. At least some of the spectral lines in the Raman light are imaged by use of imaging lens7on the detector8. A shutter14is placed in front of the detector8and the shutter14is operated based on the frame sync signal11by use of which the laser9is operated. As indicated in315, the frame sync signal11allows the detector to collect the spectral lines of the Raman light by causing the opening of the shutter14.

Fluorescence is generated by the sample according to317with a time delay with regard to the Raman light. Fluorescence light can arrive at the detector8according to319, but data about the spectral lines in the Raman signal have already been collected due to the use of the frame sync signal as shown in315which has in the meantime closed the shutter14. Thus, the detector8will not collect fluorescence light.

The data collected in315will be further processed in312, for example by use of an artificial intelligence (AI) system or the like, in order to identify the spectral lines and/or the sample. A result is output in323.

The diagram25as shown inFIG.4differs from the diagram15inFIG.3by block401. Instead of using a shutter14(seeFIG.5), double slits46and48and a scanning mirror47, for example a MEMS scanning mirror (MEMS=Micro-Electro-Mechanical System) are used, as illustrated inFIG.6. The use of a MEMS scanning mirror47allows reduction of exposure time and prevents saturation of the linear array8, trimming out the undesirable fluorescence in a different manner than shutter14.

In some embodiments, this can be similar to tandem slit scanning microscopy. A tandem scanning slit microscope is for example described in the scientific publication by Stephen C. Baer “Tandem Scanning Slit Microscope”, Proc. SPIE 1139, Optical Storage and Scanning Technology, (28 Sep. 1989); https://doi.org/10.1117/12.961780.

For example, in order to confine illumination to just the plane of focus, a tandem scanning mirror can be used similar to an epi-illumination tandem scanning pinhole microscope using slits instead. Epi-illumination is an operational mode used in microscopy in which illumination and detection occurs from the same side of the sample. The mirror image of one field aperture is coincident with the other, where an opaque mirror is used at the edge of the plane defined by the viewing slit and the center of the objective aperture. The mirror can then reflect light from the illuminated slit onto just one semicircle of the objective aperture. The remaining semicircle can be used for projecting light from the specimen to the viewing slit. Scanning can be accomplished by reciprocally rotating the two slits and the mirror. MEMS can be used to achieve rotating movements.

As further shown in diagram35ofFIG.5, the operation of optoelectronic laser9is controlled via GaN FET10. The laser9comprises an anode A and a cathode C. The anode A is connected to a voltage supply provided by a voltage source (not shown). The cathode C is electrically connected to the drain D of transistor10. The source S of transistor10is connected to ground gnd. The control signal (frame sync signal)11is applied to the gate of transistor10. The control signal10can for example be a square-wave signal, and it can be configured to rapidly switch the electric current that drives the laser9between a level at which lasing occurs and a level at which the laser9is not emitting light.

The control signal10is provided to the shutter14to open and close the shutter14in dependence on the control signal14. In the setup45ofFIG.6, the control signal10can be used to control the operation of the scanning mirror47.

The laser9is turned on and off using the GaN FET10, which can for example switch at dV/dt>100 V/s. For example, the laser9can have an approximate 8V forward bias, a turn on and off time of 160 ps is then possible. As the laser9can be a low power laser, it will not require a high voltage rail. The GaN FET10is well suited for these types of fast switching applications.

The generated pulses of the excitation radiation provided by the laser diode9is collimated using a lens12, which can produce a Gaussian beam which is desirable for accurate Raman scattering analysis. The pulses of the excitation radiation are then condensed via objective1, also referred to as probe optics, for example by using a common low f-number optics.

The pulses of laser light can be focused down to a spot size of approximately 20 microns to stimulate Raman scattering on the sample215.

The backscattered light is mostly rejected at high pass filter2, which can be a dichroic mirror, except the red-shifted component of the Raman scattered light. Thus, only the Stokes shifted light of the Raman light is further processed. The high pass filter2can start at the laser wavelength of the pulses as provided by laser9, for example corresponding to a wavelength of 520 nm, 785 nm, 850 nm, or 940 nm.

Condensing lens3focuses the pulses of Raman light through slit4which determines the resolution of the system and optical throughput. For example, a 10-50 micron slit4is used to filter the signal. The pulses of Raman light pass through collimation and aberration correction optics5, such as anachromat. The expanded and somewhat collimated pulses pass through diffracting element6which can be a 2D photonic crystal or a volume Bragg grating, and it acts as a wavelength separator.

Imaging lens7directs the first order of the spatially separated lines of the Raman light towards detector8while avoiding the zero order. The shutter14is used to prevent fluorescence light from saturating the detector8and the shutter14is operated based on the frame sync signal11.

The now wavelength separated Raman light is imaged on detector8, for example a linear array8such as a SiPM, SPAD, InGaAS detector, or cut filtered silicon with bias voltage applied.

The frame sync11can also be used to clear excess charges prior to Raman scattering being imaged on the detector8.

The linear array8can be a deep well, large pixel (for example 8 um×8 um) linear array, and it can display an extremely tight form factor (8 mm×1 mm).

A temperature sensor or TEC13can be used to monitor the laser diode temperature to account for wavelength shift of laser diode9.

As shown inFIG.7, the setup55provides multiple wavelengths of excitation radiation to sample215. This can be realized by use of three lasers9,58, and59, each of which provides laser pulses at a particular wavelength. Each laser9,58, and59is a laser diode and the cathode C of each laser diode is connected to the drain D of transistor10.

The control signal11is applied to gate G of transistor10to control the electric current through the laser diodes9,58, and59and, thus, to switch the lasers9,58, and59on and off. The control signal11is also used to control the operation of the shutter14.

A blazed diffraction grating56is further used to diffract any wavelength. For example, consider a 520 nm laser9, a 785 nm laser58, and an infrared laser59providing pulses at 1064 nm. The control signal11is again used along with a shutter14and linear array8.

As an alternative to the diffraction grating56, the Raman scattered light from the sample215under investigation can be split into its spectral lines by means of a prism or optical grating to fall onto a linear detector grid. The respective spectrum can be derived from the light intensity on each of the linearly aligned detector elements of detector8.

In some alternative embodiments, the Raman light is directed to a sensor array, where each sensitive element or pixel is using a unique filter that only allows a specified narrow waveband to reach the sensor element. In this way, a diffraction element is not required. The number of pixels and the bandwidth of each corresponding filter in front of each pixel determine the spatial resolution of the detected spectrum.

The setup65as shown inFIG.8includes double slits46and48as well as scanner47instead of the shutter14as used in setup55ofFIG.7. The control signal11is used to control operation of the scanner47, which can be a scanning mirror or a MEMS scanning mirror. A multiplexing waveguide can also be utilized. The waveguide can be used for compactly combining multiple wavelengths such as those used, for example, in communication servers.

The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the techniques and their practical applications. Others skilled in the art are thereby enabled to best utilize the techniques and various embodiments with various modifications as are suited to the particular use contemplated.