Patent Application
20080037129
a is a block diagram of a multiphoton fluorescence system consistent with an aspect of the present disclosure.;
b is a block diagram of a multiphoton fluorescence system consistent with an additional aspect of the present disclosure;
a-4c illustrate an enlarged cross-sectional views of portions of a filter consistent with a further aspect of the present disclosure;
a and 5b illustrate bar charts indicating various layer thicknesses of a filter consistent with the present disclosure;
a-6e, 7, 8, 9a, 9b, 10a, and 10b illustrate transmission characteristics of consistent with the present disclosure; and
Reference will now be made in detail to various exemplary embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
a illustrates a system 100 consistent with an aspect of the present disclosure. System 100 includes an optical source 102, such as a conventional tunable Ti:Sapphire laser, which outputs light over a range of about 680 nm to 1100 nm. Light output from source 102 is fed to a laser scan head 104, which includes conventional optical components to scan the source light over sample 108. Before reaching sample 108, however, the source light passes through filter 106, which is typically a dichroic beam splitter, as well as lens 107, which is typically a multi-element microscope objective.
Light out from source 102 typically is at a wavelength and intensity such that multiphoton fluorescence of sample 108 takes place. Light emitted from sample 108 is collected by lens 107 and directed toward filter 106. A coating, to be described in greater detail below, is provided on filter 106, which reflects light at the emission wavelengths, but passes laser light directed to the sample and reflected off of the sample. The reflected emission light is passed through filter 110, such as an emission filter, which transmits the emission light, but substantially blocks light at other wavelengths, including the light output from source 102. After passing through filter 110, the emission light impinges directly onto optical detector 114, including, for example, a photodiode or photomultiplier tube, or, optionally, is focused by a lens 112 before impinging onto detector 114.
b illustrates system 101 consistent with a further aspect of the present disclosure. System 101 includes components similar to those discussed above. In the example shown in
a is a cross-sectional view of filter 110. Filter 110 includes a substrate 210, typically made of glass or other optically transparent material. A first plurality of layers 212 comprised of alternating first and second hard coating layers are provided on a first surface 211 of substrate 210. Such hard coating layers include, for example, SiO2 (refractive index of about 1.5), TiO2 (refractive index of about 2.4); Ta2O5 (refractive index of about 2.1); Nb2O5 (refractive index of about 2.2); and HfO2 (refractive index of about of about 2.0). It should be noted that these indexes of refraction may vary slightly depending on the method and process of thin film deposition, and they also vary somewhat with wavelength. These layers and a method for depositing them are described in U.S. Pat. No. 6,809,859, which is incorporated by reference herein. A method for depositing hard coating layers is also described in U.S. Pat. No. 7,068,430, which is incorporated by reference herein. Other patents related to filters include: U.S. Pat. Nos. 7,123,416; 7119,960; 6,894,838; and 6,611,378, each of which is incorporated herein by reference. A second plurality of layers 214 is provided on layers 212. The second plurality of layers includes a repeating sequence that is comprised of at least one layer each of a third layer, first group layer, and a fourth layer, each of which has a different refractive index from the others (i.e., a third refractive index, a first effective refractive index, and a fourth refractive index, respectively). A third plurality of layers 216 is further provided on second surface 213 of substrate 210. The third plurality of layers also includes a repeating sequence that is comprised of at least one layer each of a fifth layer, a second group layer and a sixth layer, each of which has a different refractive index from the others (i.e., fifth refractive index, a second effective refractive index, and sixth refractive index, respectively). As used herein, the phrase “group layer” means one layer or a plurality of sub-layers. Alternatively, the layers 214 may be provided on second surface 213 and layers 216 can be provided on layers 212.
Consistent with a further aspect of the present disclosure, layers 212, 214 and 216 may be provided on the same surface, e.g., surface 211, of substrate 210 (see
n=exp[aln(nSiO2)+(1−a)ln(nTa2O5)], where a=0.382
For nSiO2=1.5 and nTa2O5=2.1, n=1.8238 for a given reference wavelength within 840 nm to 950 nm. An optimal intermediate index value can be determined in a known manner, for example, as described in P. W. Baumeister, Optical Coating Technology, Section 5.3.5, the contents of which are incorporated herein by reference.
Because of practical limitations with materials, equipment, and processes, it is not always convenient to deposit intermediate-index layers with a refractive index sufficiently close to the required index to achieve the desired performance. As a result, an alternative approach is to replace each intermediate-index layer with a sequence of multiple, thinner “sub-layers” with indexes of refraction that are different from that of the intermediate-index layer, and which together approximate the optical performance of the single intermediate-index layer. Such a sequence of layers is known as a “Herpin equivalent layer.” For example, each of the single, intermediate-index first group layers (214-2 and 214-4 in the above example) may be replaced by a sequence of two or more relatively thin sub-layers as illustrated in
In a similar manner, as shown in
Due to the presence of the Herpin equivalent layers in layers 214 and 216 a relatively large number of layers is often formed on substrate 210. In addition, many of the Herpin sub-layers are relatively thin and have thicknesses less than 20 nm. Layer deposition techniques as described in U.S. Pat. No. 7,068,430 may be employed in order to form layers 212, 214 and 216 shown in
Other combinations of hard coating layers may also be provided. For example, each of the second layers, each of the fourth layers, each of the sixth layers, each of the second sub-layers, and each of the fourth sub-layers may include hafnium oxide (HfO2). Alternatively, each of the second layers, each of the fourth layers, each of the sixth layers, each of the second sub-layers, and each of the fourth sub-layers may include niobium pentoxide (Nb2O5), titanium dioxide (TiO2), or aluminum pentoxide (Al2O5).
a and 5b are bar charts indicating exemplary optical thicknesses (in quarter wavelengths of a 550 nm reference wavelength) of layers 212 (see range 512,
a illustrates a transmission characteristic 610 as a function of wavelength associated with filter 110. Transmission characteristic 610 has a relatively high average transmission, e.g., greater than 80% and preferably greater than 90% over a transmission band or first band of wavelengths 612, extending, for example, from about 300 nm to about 700 nm, corresponding to the range of wavelengths of emitted light typically generated in a multiphoton fluorescent system. Filter 110 also has first, second and third blocking levels or an amount of optical blocking with an OD greater than 5 and preferably greater than or equal to 6 over second 614 (about 700 nm to about 840 nm), third 616 (about 840 nm to about 950 nm), and fourth 618 (about 950 nm to about 1100 nm) wavelength bands, for example. The second, third and fourth wavelength bands collectively correspond, for example, to the range of wavelengths associated with the light output from a Ti:Sapphire laser. The presence of the intermediate-index layers or Herpin equivalent layers in layers 214 and 216 substantially reduces the second and third order stop bands in the wavelength band of 300 nm to 700 nm and provides improved transmission in this spectral region, as noted above.
b,
6
c, and 6d illustrate transmission characteristics 620, 630, and 640 having corresponding wavelength blocking bands 614, 616, and 618, respectively. Wavelength blocking bands 614, 616, and 618 are associated with layers 212, 214, and 216, respectively.
e illustrates multiple transmission characteristics corresponding to those shown in
An additional example of a filter 110 having the structure described above has an average transmission greater than 80% over a first wavelength range extending from a first wavelength equal to 380 nm to a second wavelength between 650 nm and 720 nm. This optical filter also has an average optical density (OD) greater than 6 over a second wavelength range extending from a third wavelength, which is greater than the second wavelength and is between 680 nm and 750 nm, to a fourth wavelength equal to 1100 nm. The third wavelength exceeds the second wavelength by an amount less than or equal to 30 nm. Preferably, the optical filter has an average OD greater than 8 over a third wavelength range extending from the third wavelength to 1040 nm. In addition, the optical filter may have an average transmission greater than 90% over a fifth wavelength range wavelength range of 400 nm to 650 nm.
It is noted that relatively precise monitoring may be required to deposit layers 212 and 214 on surface 211 of substrate 210. Cutoff edge 615 (see
Consistent with a further aspect of the present disclosure, layers 212 can also include either intermediate-index or Herpin equivalent layers, but with increased complexity, thus possibly requiring four separate filter designs on two substrates.
Further exemplary transmission characteristics 710 and 810 are shown in
Layer structures associated with the filters having the characteristics shown in
In addition, HfO2 may be employed, as noted above, instead of Ta2O5. In that case, UV transmission may be increased and the high transmission band can be extended to lower wavelengths due to the lower material absorption associated with HfO2 at wavelengths below about 330 nm.
Another transmission characteristic 1300 of an exemplary filter 120 is shown in
Other embodiments will be apparent to those skilled in the art from consideration of the specification. For example, instead of both layers 214 and 216 including Herpin equivalent sub-layers (see
Furthermore, layers 214 may be provided without layers 216. In that case the filter may have a transmission characteristic similar to that of transmission characteristic 610, with relatively high average transmission, e.g., greater than 80% and preferably greater than 90%, over a transmission band or first band of wavelengths 612, extending, for example, from about 300 nm to about 700 nm, and first, as well as second blocking levels over second and third bands of wavelengths, respectively. The second and third bands of wavelengths include wavelengths greater than 700 nm. Each of the first and second blocking levels has an average optical density (OD) greater than or equal to 5 and preferably greater than or equal to 6. The second and third bands being associated with layers 212 and 214, respectively. Layers 212 and 214 are associated with a respective, first and second transmission characteristic, and each of the first and second transmission characteristics has an average transmission greater than or equal to 80% over the band of wavelengths extending from about 300 nm to about 700 nm.
Further, consistent with the present disclosure, filters may have transmission characteristics in which the wavelength bands or ranges of high and low transmission may be scaled. In particular, such optical filters may have an average transmission greater than 80% over a wavelength range extending from a wavelength λa (λa is a wavelength between 300 nm and 600 nm) to a another wavelength between λa (650/380) and λa (720/380) (“λb”). Such optical filters may also have an average optical density (OD) greater than 5 and preferably greater than 6 over a range extending from a wavelength, which is greater than λb and is between λa(680/380) and λa(750/380), to a wavelength equal to λa(1100/380).
Accordingly, for example, as shown in
As discussed above, filters consistent with the present disclosure provide relatively high transmission over a wavelength range of about 300 nm to 700 nm, but have high blocking from about 700 nm to 1100 nm. Such filters are thus suitable for multiphoton fluorescence applications in which blocking of Ti:Sapphire laser wavelengths and high transmission at sample emission wavelengths of 300 nm to 700 nm are desired.
It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
The present application claims the benefit of provisional Application No. 60/799,647 filed on May 12, 2006, the contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60799647 | May 2006 | US |
