Laser - Science topic

My guess is that light scattering is the problem. Bacterial suspensions scatter light, which is why they are turbid. (Turbidity is actually used as a standard measurement of bacterial cell density. This is known as the McFarland measurement and there is a special instrument for measuring it.) The denser the bacterial suspension, the more light scattering interferes with detection of the laser-induced fluorescence. At a high enough density, there will even be multiple scattering as another effect. I would expect LIF to give a linear result only for very dilute bacterial suspensions.

Additional confounding effects may arise from differences in the growth phase of the bacteria, their shape, their degree of aggregation, their species, and whether they shed any outer membrane vesicles or other scattering substances into the medium.

Ortamın sıcaklık değeri için Sıcaklık ölçerin yapıldığı malzemenin yapısına ve sıcaklık haznesinin içindeki sıvının cinsi ortama uygun olacak şekilde seçilmeli.

I wanted to show a drawing but I couldn't insert it.

I am confused. The Mai-Tai has a slightly shorter pulse so it's bandwidth should be slightly greater than the Vitesse. Looking at the data sheet for the Vitesse, the specified bandwidth is >10nm (FWHM), but probably is not much greater than 10nm if the pulse width is 100 fs at a central wavelength of 800nm. A 30 nm bandwidth would support 25 fs pulses assuming a sech squared temporal profile.

Yes, high-power Q-switched lasers with 100 ns pulses exist, but they are rare. Custom solid-state or hybrid systems may be required.

The loss feature peak in XPS spectra after laser etching of lead-based perovskites likely results from structural degradation caused by laser damage. The peak intensity may correlate with the degree of structural deterioration, reflecting changes in electronic structure or defect states.

There used to exist Prometec Laserscope. Ages ago, I was using it for beam scanning of 2 kW CW CO2 laser. It is mentioned in the paper:

It is not suitable for pulsed lasers, unfortunately.

For pulsed laser, you may try a method I was using for pulsed YAG lasers. You need several 100% mirrors deposited on transparent material in such a way that the transmitted beam is not distorted. After the mirror, you have an attenuated laser beam with the power of about 0.5% from the incident beam.

You repeat mirrors as necessary. However, remember that the reflected beam should not return directly into the laser. The whole system must be skewed a little as to prevent damage to the laser and multiple reflections. Perhaps 45 degrees mirrors are the most convenient, safe and easy to use. On the path of the reflected beam, you need an absorber.

Attenuated pulse may be analysed by suitable methods. Hence, now your problem is reduced to low-power laser pulse analysis.

Every so often, an analysis of craters burned in an acrylic plate can be enough. It is quite accurate as long as the laser fluence is not too high, and using profilometers provides accuracy of crater measurement.

At first, you may try burning a crater with a beam which is not attenuated, and asses the results.

Maybe widening the beam with a lens will suffice.

Do not inhale the fumes from acrylic, they are poisonous.

Do not put the acrylic plate too close to the laser and optical elements.

Ihtisham Khalid thanks for your response. about triangulation-based approach, Should I find the cosine factor correction for each point seperatyely?

There are three major laser mask-making techniques. The first is to directly remove the thin films of the photomasks (laser engraving). The second is to use laser beams as the light source to expose photoresists covered on the photomasks (laser-based lithography). The third is to generate patterns on the photomasks via photoresist (laser pattern generation).

Dear Joao Ricardo Duda ,

there is a very low chance that one of the authors will see your question here...

I found that paper here on RG:

You may open that publication and add your questions as a comment to that publication...

Best regards

G.M.

Dear John

Thanks alot for your concern and advice, I've been through your sugestions and found nothing wrong for sure. It seems to be a soldering issue since the device started working again.

The decay in power persists till know, do you suggest buying new flashlamps? since the ones we have came with the device 21 years ago.

Short answer: no.

The coherence length defines a distance over which if you know (or control!) the phase at location A the phase at location B is no longer related to the known phase at location A. The phase at location B wanders with respect to the phase at location A and averaging over a short time B goes through all possibilities. So at any given moment the difference in phase between point A and point B is random. Well, technically the coherence length is defined at a location where the phase isn’t quite yet completely uncorrelated but it’s getting there.

So, if you hold the phase of laser X constant relative to the phase of laser Y, but then you combine them at a point where their path lengths have differed by more than a coherence length, then their phases will no longer have a fixed relation. They aren’t coherent, and you won’t get the beam quality expected of coherent beam combining.

No, I’m afraid that isn’t enough information. Fluence is energy per unit area, and you won’t be able to determine the fluence without determining the profile of the beam spot.

So, what energy and what area? Well, for average fluence, you could use any area you like. If you shine the laser at a 3x3 m wall, the average fluence on the wall is 16 uJ per 9 square meters. But, of course, that isn’t very interesting. You know most of that area is seeing no fluence, and there’s a much smaller area that is experiencing a much higher fluence. That’s an exaggeration, but even if you use an area roughly the diameter of the beam, that’s still an average and there will be portions of the beam that are producing higher fluence on a smaller size scale. What area you use depends on what you want to know and also on the size scale of features of the beam profile.

Usually people are interested in size scales smaller than the beam. For example there are physical processes that require a threshold fluence to get started. Others are nonlinear and are very sensitive to the peak power. So, maybe you want to know the highest fluence seen on a very small size scale. The interesting size scale might be determined by the process you are investigating. Or, if your beam profile is very smooth, (like for example a Gaussian) then there is a size scale over which the beam intensity doesn’t change much, so the integral over that area approaches the local value.

For whatever area you choose, you need to determine the fraction of the laser energy that passes through that area. It can be a great help if you have a known calculable beam shape. For example, if you know your beam is Gaussian, you can relate a measurement of a large part of the beam to the beam profile and then determine the fluence over any part of the beam by computation. Suppose you have a beam profiling camera. In the image you can find the centered circle that contains 87% of the total energy. That is the 1/e^2 diameter. The average fluence is 87% of the measured energy over the aperture. However, knowing the shape, you know more than that. You now can infer the whole profile. For instance the peak fluence in the center of the Gaussian is 2 X the average fluence in the 1/e^2 circle. Etc.

Hi, Luigi. You may want first to try turning off your laser, cover all LEDs with black tape and darkening your room to use the confocal photomultiplier(s) as detectors for the bioluminescence signal (although I guess the lightpath will be larger than the optimal—too much signal loss)

About your question: In confocals the emission is detected simultaneously with sample irradiation. Did you somehow separate the excitation from emission reading?

Wow! Not much optical path length in that crystal!

I think your plan with the UV cure adhesive sounds fine. We more often use a thermally cured epoxy like Ablebond or Minbond, but we’ve had good luck with UV cured adhesive in less challenging uses.

There are just a couple things to consider. It doesn’t stick until the UV light hits it, so you’ll want perform the mounting in an orientation where gravity helps keep it in place until you cure the glue. A similar point: it doesn’t stick unless UV light gets to it. It doesn’t look like an issue here: it’s just a thin plate and BBO is transparent to the curing light. But, the point is, you want to be sure the curing light gets to the glue.

The one think that concerns me: why did it debond in the first place? Glued at the corners, there is little thermal conductivity. Do you think there might have been enough absorption in the BBO to cause any differential thermal expansion? This looks like a simple arrangement where that isn’t an issue, and SHG in BBO generally doesn’t deposit much heat. Nevertheless, it might have come unglued for a reason.

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May be your laser contains the hydrophillic component? May be the electric supplying of pumping system was slightly damaged (capacitors or transistors)? May be active media (or output mirror of cavity) slightly damages due to the dust in air and its adsorption on the surface of mirror. It is necessary to use air stream to realize processing of mirror. Check all the component of system or ask offices of company.

Çürük lezyonları tespit etmek, lazer floresanın gücüne bağlı. Bir de lezyonların nasıl yerleştirildiğine bağlı. Buradan elde edilen veriler kaydedilir.

Dear Rachel Escue ,

I con not comment on the photo bleaching, but on the mounting of 35 mm glas bottom dishes (I assume that is what you meant with cover slip dishes). I have used WPI FD35-100 extensively and always used round cover slips (Thermo Fisher) with them. You/he should get some 1-2 mm lower than you inner plastic circle. Than I have cleaned them with some paper and applied a drop of mounting medium to the round coverslip. Than I turned them with tweezers, so that the drop is hanging and all bubbles go to the out side of the drop. Afterwards I just put the coverslip onto the glas bottom (without buffer just residual humidity) and it's even possible to push then the rest of the buffer and bubbles to the edges (with the back of the tweezers). He can have some test runs without the actual sample.

Best wishes Soenke

The polarization does not affect the strength or depth of the evanescent wave, but it does directly determine the polarization of the evanescent wave. See, for example, this animation.

The polarization of the evanescent wave can have a strong effect on how well the light interacts with the sample, particularly if the sample is ordered and the polarizability differs in different directions. However, even in an isotropic medium the existence of the interface itself breaks symmetry and changes the response depending on polarization.

Let a bit continue.

So, in principle, really there can be some “absolute vacuum” – empty “Information” Set, however that is absolutely fundamentally impossible – information absolutely for sure cannot be non-existent, and so the Set exists being non-empty absolutely always – “in absolutely infinitely long time” having no Beginning and no End;

- and only concrete empty sets that relate to concrete informational patterns/ sets of the patterns can exist.

In this thread a concrete informational system/set of informational patterns/systems “material objects” “Matter” is considered, and in this case the general empty sets – or “vacuums” can exist as:

- “absolute vacuum, that was till the conserve can “There is no informational system “Matter” in the Set” was opened by some energy, let - 13.8 billions of years ago, when the first Matter’s FLE was really created, and

- “matter vacuum” when only the first version of the FLE-lattice was created and existed till at the inflation epoch, i.e. though the quite material objects “FLEs” existed, but “matter”, i.e. observed now a huge number of particles didn’t.

That’s all, after in the first FLE-lattice version corresponding a huge energy portion was pumped, and so the particles, which are some disturbances in the lattice, were created, no “vacuums” exist;

- including there are no such things as “vacuum where existed created/annihilated “virtual particles and fields”, in Matter only real particles, and real the Forces mediators/real fields, which constantly and always are created by their charges, exist.

Cheers

Hello! Here is the datasheet Tawsif Ibne Alam Gerhard Martens

*Fluorescence Lifetime Measurement (FLIM)*

Principle:

1. Excitation: Diode laser emits continuous wave (CW) light.

2. Fluorescence: Sample emits fluorescence in response.

3. Lifetime measurement: Detect changes in fluorescence intensity over time.

Setup:

1. Diode laser (cw)

2. Sample chamber

3. Photodetector (e.g., PMT, APD)

4. Data acquisition system

Measurement steps:

1. Illuminate sample with cw diode laser.

2. Detect fluorescence signal.

3. Measure fluorescence intensity decay.

4. Analyze decay curve to extract lifetime.

*Lifetime calculation:*

1. Exponential fitting: Fit decay curve to exponential function.

2. Lifetime (τ) calculation: τ = 1 / (decay rate)

*Advantages:*

1. High sensitivity

2. Fast measurement

3. Non-invasive

*Applications:*

1. Biomedical research (e.g., protein binding, cell imaging)

2. Materials science (e.g., quantum dots, nanocrystals)

3. Photovoltaics (e.g., solar cell efficiency)

*Diode laser specifications:*

1. Wavelength (e.g., 405 nm, 633 nm)

2. Power (e.g., 10 mW, 100 mW)

3. Stability (e.g., <1% intensity fluctuation)

*Common fluorescence lifetime ranges:*

1. Biological samples: 1-10 ns

2. Organic materials: 1-100 ns

3. Inorganic materials: 10-1000 ns

Nanometre birimi metreye çevrilir ve piksel cinsinden karesi alınır. 2L olarak hesaplamanın nedeni mod kilidi 2n (tekrarlama) nedeniyle, n-1 ve n-2 tek ve çift girişimi sıralaması için yapılır.

Thanks for the answer Hüseyin!

Removing the interferometer block was an unnecessary and dangerous way to resolve this issue. The solution was quite simple.

SETI (Search for Extraterrestrial Intelligence) does not need to be fixed exclusively on radio-collimated signals, but radio waves are a primary focus because they can travel vast distances through space with minimal interference. However, SETI also explores other methods, including optical and infrared signals, to broaden the search for potential extraterrestrial communications.

spektral fitreleme kullanarak yeşil emisyonu bastırmak için kullanılabilir, böylece istemediğimiz emisyonları optik yolda filtreleriz. Farklı olarak katkılama işlemleri yaparak iyonları doğrudan erbium iyonlarına aktarmak yerine daha verimli şekilde pompa enerjisinin 1550nm emisyonunda kullanımı sağlanabilir. Ayrıca yukarı dönüşüm verimliliği sıcaklıkla düşürülebilirliği ele alınabilir. Çalışma dıcaklığı kontrol edilerek yeşil emisyonu azaltılabilir ve 1550 nm ye olan enerjiyi yenlendirebiliriz R.P. Wang

Hi Rodriguez,

UW LASER is engaged in laser-scriber for the photovoltaic industry.

Mesafe arttığı için lazer ışık kaynağının da uyarma etki süresi uzar ve zamanla aynı sürede aynı miktarda etki edemez.

Thanks Mike Albert for your detailed and informative answer.

Try to check this one, if you need very brief theory:

Ma, ZC., Chen, QD., Han, B. et al. Measurement of Two-Photon Absorption Cross Section of Metal Ions by a Mass Sedimentation Approach. Sci Rep 5, 17712 (2016). https://doi.org/10.1038/srep17712

Thanks you!

Thank you for the information sir

Hi,

Yes, of course, this issue was discussed in section 4.2 of this paper:

Makara ve ip gibi basit makineleri düşünebilirsin. Makaranın yükü arttıkça uygulanan kuvvet ve ipteki gerilim artar. Buna göre lazerin gücü arttıkça yapışma mukavemeti artar. Alt tabaka tüm yükü taşır ve sağlam olmak zorunda. Telin bağlama gücü, alt tabakanın oluşumu sırasında lazer tarafından uygulanan güce bağlı olur.

Likely you're using a Raman microscope for your measurements. Try to use the lowest magnification objective, this should increase the spot size.

(In the limiting case, you could try to completely remove the objective (just unscrew it) and excite the sample with the unfocused beam. Though the collected signal could become very small in this case.)

Güneş enerjisi saf fotonlarla elde edilebilecek en verimli ve zararsız enerjiye sahiptir. Bu nedenle heryerde kullanılabilir. İletişimde ise yaydığı zararsız dalgalar ve ışınlar nedeniyle kullanılabilir. Hatta iletişim fotonlarla sağlanabilir.

Yes, it's possible. Laser-based techniques, like Raman spectroscopy and laser-induced breakdown spectroscopy (LIBS), have been used to detect microplastics in water samples. These methods utilize the interaction between laser light and the chemical composition of the microplastics to identify and quantify them.

Alwielland Q. Bello

Aristides Marcano Olaizola

Şükrü Aktaş

Thank you Harri

I supposed it would go as you describe. Good to hear it by experimentalists. I am a little afraid that when using a mask (fibers even more) diffraction can spread my rays but I suppose it would be negligible as the holes would not be to narrow but at 1-2 mm.

Regards: Ilian

PS. By the way what is the easiest practical way to rotate polarization from V to H. Can you recommend a rotator of polarization? Of course sugar water solutions can do but I look for something more compact.

Ahmed A. Aktafa

Nanoparticles produced by ablation are dependent on laser energy. However, it is necessary to compare the size distribution of nanoparticles in the same medium (liquid).

Dear Wedad A. Alwesabi , thanks for your interesting question.

Raman spectra are not dependent on the excitation laser wavelength, sometimes we choose a laser with a wavelength or another to avoid interferences casused by luminiscence, which can mask the Raman bands.

Note, it is always useful for us in order to help you, to know what excitation laser you used and what settings did you choose to obtain your Raman spectra.

Magnetite has five Raman active modes, applying group theory to its spinel structure, according to literature these vibrational bands appear at around: 193, 306, 450-490, 538, and 668 cm-1.

But it happens that two of those five modes (193 and 450-490 cm-1) are really weak, and often they are not reported in many cases, specially when the sample is measured at room temperature and for nanoparticle samples.

Bands at 306 and 538 cm-1 are weak but often they can be seen in a Raman spectrum of magnetite. The more strong band is the one appearing around 668 cm-1, this one is the more characteristic or distinctive of magnetite.

However you cannot find this band in your experiment and from your XRD you know you actually have magnetite.

May be the answer for this question is related to the thermal stability of magnetite, which when heated in air transforms into maghemite and finally into hematite. These transformations can be induced by the laser power used during Raman measurements, due to energy transfer and heating in the sample under the laser spot. Raman spectra of maghemite and hematite do not contain the band at 668 cm-1 characterist of magnetite, while some bands from these materials could appear near the other two bands of magnetite, what together with the XRD results could cause confusion.

Several articles used the laser power variation to observe these transformations.

So it would be a good idea to repeat your Raman experiments with a fresh sample of magnetite and a low laser power. You could start with the lowest possible on your spectrometer and rising it step by step untill you get a good Raman spectrum of your sample.

Here you can find some articles about the topic:

Hope you find this answer helpful, if you need some extra explanation, please don´t hesitate to contact.

Regards

If it only reaches 13% of your maximum excitation potential, you won't get a good excitation signal, you are risking incaccurate results.

Bant içi yapısını malzemenin yapısı ve atomik yapısı hakkında bilgi sahibi olduğunuz kadar hayal edebilirsiniz.

Samanyolunda farklı türde ışık kaynağı var. Yıldızlar bu ışık kaynaklarından bazıları. Yıldızların bir kısmı kendiliğinden ışık yayar, bir kısmı ise diğer ışık kaynağı yardımı ile yayar. Işık kaynağı yardımıyla parlayan yıldızlar zamanla sönebilir veya kendiliğinden ışık yayan yıldızlar uzaydaki büyük olaylar sonucunda yok olabilir. Bu parlama ve sönme aşamasında alfa, beta, gama ışınları yayabilir. Kendiliğinden ışık yayan yıldızlar ise patlama sırasında ise x ışınları, radyo dalgaları, alfa, beta, gama gibi ışınlar yayar ve uzay ortamında farklı etkiler bırakır.

electron beam welding provision is there or not in comsol multiphysics

Lazer ışınının çift geçişi, eğer ışın miktarını etkilemeyecekse herhangi bir sorun olmaz.

I can English a little bit.

The instability in the process of laser plasma expansion arises from a multitude of factors that influence the dynamics of the expanding plasma. Hydrodynamic instabilities, including Rayleigh-Taylor and Richtmyer-Meshkov instabilities, emerge at the interface between the laser-produced plasma and the surrounding medium, leading to mixing and irregularities in plasma expansion.

Additionally, self-focusing effects can occur due to the nonlinear response of the plasma to intense laser fields, resulting in filamentation or channeling within the plasma. Nonuniform heating, whether from variations in laser intensity or material properties, can cause uneven expansion velocities and density gradients, triggering further instability. Collisional effects and the presence of magnetic fields also contribute to complex plasma dynamics, altering expansion behavior and stability. Radiative cooling further complicates matters, as it affects energy balance and can lead to fragmentation or condensation of the plasma. Moreover, pulse-to-pulse variations in laser parameters or target conditions introduce stochastic fluctuations, exacerbating instability.

Understanding and mitigating these instabilities are vital for applications such as laser fusion and plasma-based accelerators, necessitating a combination of theoretical modeling, numerical simulations, and experimental diagnostics.

Resources such as scientific journals like "Physics of Plasmas," "Journal of Applied Physics," and "Physical Review Letters" provide valuable research articles on laser plasma dynamics and instability mechanisms, while textbooks like "Fundamentals of Plasma Physics" by J.A. Bittencourt offer comprehensive insights into plasma behavior and instabilities. Additionally, research groups and laboratories specializing in laser plasma interactions, such as the Lawrence Livermore National Laboratory's National Ignition Facility (NIF) or the Max Planck Institute for Plasma Physics, conduct experimental studies and provide valuable data for understanding and addressing plasma instability challenges.

The polarization rotation angle of linearly polarized light is proportional to the spin projection along the propagation direction of the light.

Ah. Ok. So the meaning of the focal length of a positive lens is clear, right? Parallel rays coming from the left are bent by the lens towards the axis and all meet at a point to the right of the lens called the focus. The distance between the lens and the focus is the focal length. You can think of that focal point as a “real image“. Those parallel rays from the left are from some distant point source. Those rays coming together at the focus are like a new point source. If you continue to they right it would appear to anybody to the right of the focus that all the light is coming from that focus. In fact, if the distant object is not a point source, but something big enough to resolve (say, the sun for example), there will be an image of the object formed at the focus, and, again to anyone to the right of the focus it will appear as if the light is coming from an object (for example a tiny sun) located at the focus.

With a diverging lens the rays are bent away from the axis and they never come together at a real focus. However, if you trace the rays backwards, it looks as though all the rays are coming from a point to the left of the lens. The distance between the lens and this virtual source point is the focal length.

In either case, someone looking from further to the right will see the light as coming from a source located at the focal point. In the positive lens case the light will seem to originate (and actually will originate) from a point to the right of the lens. In the negative lens case the light will seem to originate from a point to the left of the lens. If we take the lens axis to be a spatial axis with the lens at zero and the downstream direction (to the right in my example) as positive, then a positive lens makes a real image on the positive side of the lens and the negative lens makes a virtual image on the negative side of the lens.

Fairly common effect. Often due to resonance issues. Take a look at graphene Raman spectra - well documented changes with excitation frequency. However, it doesn't look like you have much change in the figures that couldn't just be sample prep issues.

Dear Leonid, thanks a lot. We will have a look at their products.

best

I've just updated the document. The normalization is corrected now. Before there was a deformation of the photons' paths.

Ijaz Akbar.

Absolutely, it depends on the inherent properties of the material used, such as reflectivity, thermal conductivity, and absorption coefficient, which play a major role. Metal powder characteristics, like particle size and surface morphology also impact efficiency. A, rougher surfaces can scatter the laser beam, reducing its efficiency.

While the printer brand may have a less impact on efficiency. If the printer is well-calibrated for the specific material, it's still a contributing factor.

Depending on the wavelength of the laser and absorption characteristics of the film, damage may occur even before apparent heating and melting take place

Hi Manon! Any luck? Have you solved the issue?

The Conservation of Energy rule applies to a laser beam passing through a system or subsystem such as a telescope. Most of time, laser beam energy or power passing through a telescope will obey the following version of the conservation of energy rule:

P = T + R + A + S

Here “I” is the power input to the telescope and “T” is the power of the beam that is observed exiting the telescope. The losses are then “R” for reflection losses, “A” for absorption losses, and “S” is for scattering losses.

Reflection losses occur at each lens surface - these are specular reflections.

Scattering losses are just that, scattered light. Scattering losses occur in the bulk substrate and coatings of the lenses and are dependent on the wavelength of light and substrate/coating materials.

Scattering will also occur when a laser beam is too large for the telescope aperture. When this occurs a portion of the beam striking the telescope outside the lens clear aperture will be scattered.

Some of this light hitting the telescope body will also be absorbed in the housing.

Finally, absorption losses occur in even the best optics. Anytime a light or laser beam passes through an optic, a (hopefully 😊) small portion of the laser beam will be absorbed in the coatings and substrate materials of the lenses.

Second question: “Is there any relation in between laser power to telescope aperture?” For gaussian laser beams this is simple to answer using the power through an aperture equation. Wikipedia provides a good explanation of this at:

See specifically the section titled “Power through an aperture.” Of course, other types of laser beams require optical modeling in most cases.

This is by no means a comprehensive review, but I hope it helps a little!

You will also find some interesting information about lasers and optics at

If your interest is in gaussian beam stuff, click through to:

(you can log in as guest if you don't want to create an account - there is no charge in either case)

Gary

Katayoun Salem any given beam area?

IGBT levhalar ince bir yapıya sahip oldukları için katmanlar arasında herhangi bir kusur olduğu zaman levha zeminine gelen dalga kılavuzu hasar bırakır. Tavlama sırasında kimyasal olay meydana gelir. Dalga kılavuzu mikro dalgalar vb. dalga yayar. Tavlanmış zeminde kusur olması tavlama sırasında buzlanmaya neden olur. Buzlanmanın nedeni tavlama sırasında ışık ışınlarının malzeme kusurlarından dolayı ortamda bulunan gazlar vb. maddelerle tepkime vermesidir.

A laser beam can be focused to an astonishingly small spot size. For example that is how they make the tiny features on your computer chips (at least down to the 50nm node anyway). The size of the focal spot depends on the wavelength and the cone angle. For a near diffraction limited beam you will get an Airy pattern. The radius from the center of the spot to the first Airy null is 1.22 x (wavelength) x NA where NA is numerical aperture and is the sine of the half cone angle.

Many lasers are nearly diffraction limited and can achieve something very close to the diffraction limited spot size. However others are not. Choices in how the beam is formed or aberrations in optics spoil the beam. This is called the beam quality. It is compared to the perfect diffraction limited beam by a parameter “M”. You would say that the beam is “M times diffraction limited”. Then the smallest spot size is M^2 the diffraction limit.

In your case the trick is the NA. How close together can you squeeze 4 lenses? And it’s not just the lens size, it’s the size of the beam going into the lens that determines NA. To avoid working with tiny lenses and short focal lengths you might want to expand the beam beam so it nearly fills a reasonable sized lens. The beams can be tilted towards each other to put the spots close together as you show, but that gets harder and harder as the NA gets larger.

So, for example, suppose we have 2 HeNe lasers (almost always very nearly diffraction limited) We expand the beams so the 1/e^2 diameter is 10 mm and put them into good aspheric lenses with diameter = 12.5 mm and focal length = 10 mm. That gives an NA of about 0.45 and a long enough focal length that the beams can be tilted together to put the spots next to each other as you show. In that case the Airy radius is about 1/3 of a micron. As I said, astonishingly small.

Basically yes. If possible one should design and simulate the system.

Fluorescent photochroms have been studied in Japan. But I wonder if some are commercially available.

Received, thank you for your answer。

James Garry Hey mate, really appreciate your response to my question! It may sound really silly, apparently I have solved the issue by resoldering my microsensor. Now it works fine. Once again, thanks for the help mate!

You find a lot of explainations of the technology, if you use a search engine. Anything particular you don't understand?

Second harmonic generation (SHG) occurs when two laser beams beat in a plasma, producing harmonics. The process is more efficient when the beat frequency is the same as the resonant frequency. When the modulation frequency is twice that of the incident laser beams, the strength of the combined electric field is modulated. The efficiency and circumstances of SHG observation depend on experimental setup, laser properties, and plasma parameters.

dB is a logarithmic scale but laser beam intensity is measured by Photons per squared cm because it will be difficult. But you can normalize your laser beam intensity of signal by using some famous intensity such as output intensity of laser or unfocused laser beam intensity or by using output laserbeam intensity according to the specification of laser equipment.

The higher the mode, the greater its losses, therefore only a certain number of the lowest modes are excited in the resonator. An unstable resonator has high losses for all modes, so only one or two “matching” the resonator geometry are excited in it. Which modes these will be, it depends on the specific geometry.

Do you align the polarization of the laser to the axis of the fiber? It is absolutely necessary to align it to within a few degrees to avoid beating between the two output polarization modes. If your laser isn't polarized you'll need an extra polarizer.

Dear friend Renato Beraldo

Alright, buckle up because I am here to tackle the Raman spectroscopy challenge with unbridled enthusiasm!

Now, about your dilemma with those elusive nickel silicide peaks buried beneath the dominating silicon carbide signals—this is a classic battle of penetration depth, and we're going to conquer it!

1. **Adjust Laser Wavelength:**

- Try using a laser with a longer wavelength. Longer wavelengths generally penetrate deeper into materials. Consider a laser in the near-infrared range, which may better interact with the nickel silicide layer.

2. **Utilize Multiple Excitation Wavelengths:**

- Employ different laser wavelengths to selectively excite different materials. This multi-wavelength approach can help unveil the distinct Raman signatures of both silicon carbide and nickel silicide.

3. **Optimize Laser Power:**

- Adjust the laser power. Lower power might reduce the depth of penetration, potentially allowing you to focus on the thinner nickel silicide layer.

4. **Confocal Raman Microscopy:**

- If available, consider using confocal Raman microscopy. This technique uses a pinhole to eliminate out-of-focus light, enabling better depth resolution.

5. **Enhance Signal from Nickel Silicide:**

- Experiment with enhancing techniques. Surface-enhanced Raman spectroscopy (SERS) or resonance Raman scattering might amplify the nickel silicide signals.

6. **Thin Sectioning:**

- If feasible, consider thin sectioning your sample. Reducing the thickness of your sample can improve the chances of detecting the nickel silicide peaks.

7. **Sample Preparation:**

- Optimize sample preparation. Ensure a smooth and uniform surface. Any irregularities might affect the depth of focus.

8. **Collaborate and Seek Expert Advice:**

- Don't hesitate to reach out to Raman spectroscopy experts or collaborate with researchers who specialize in similar materials. Their experience could provide valuable insights.

Now, go forth, fearless experimenter Renato Beraldo! Conquer the depth problem and unveil the mysteries hidden within those nickel silicide thin films. I believe in you!

Cold spraying can be used to preset powders. By adjusting the process parameters of cold spraying, different layer thicknesses and uniformity levels of preset powder layers can be obtained

Photo-resistors are typically not used for quantitative measurements due to temperature drifts, etc. I would recommend to use photodiode instead, e.g. https://www.electronics-lab.com/project/photo-diode-amplifier-visible-light-using-opa381-arduino-nano-shield/

Either green or red should be ok with silicon photodiode.

The key parameters that can influence the size, shape, and properties of the nanoparticles produced are: Laser Parameters, Wavelength, Pulse Duration, Pulse Energy, Target Material, Type of Material, Liquid Environment, Type of Liquid and Experimental Setup and so on…