Junaid, simplest idea of reducing laser power below 10% is to use surface reflection over a glass plate. If the refractive index of the glass is 1.5 at the green laser wavelength, normal reflectance is given by ((1.5-1)/(1.5+1))^2=0.04. Shigeo

Dear Junaid

You mentioned to use a polarizer and half waveplate to change the light intensity. That is the best way to use within a microscope system. You could buy very cheap sheet polarisers to test.

Hope it helps.

Bw

Xuhua

Perhaps you can look at something like

Continuously Variable ND Filter,

https://www.thorlabs.com/thorproduct.cfm?partnumber=NDL-10C-2

https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=2876

Also you can power the laser diode (via series 47ohm resistor or so) and power it by variable duty ratio pulse generator like FY6900

https://www.banggood.com/FY6900-Dual-Channel-DDS-Function-Arbitrary-Waveform-Signal-Generator-Pulse-Signal-Source-Frequency-Counter-Fully-Numerical-Control-20MHZ30MHZ50MHZ60MHZ-p-1495502.html?gmcCountry=IE¤cy=EUR&createTmp=1&utm_source=googleshopping&utm_medium=cpc_bgcs&utm_content=haosen&utm_campaign=ssc-ie-all-0310&ad_id=424489510797&gclid=Cj0KCQjw0rr4BRCtARIsAB0_48OqKIgLahG0fTEfbpeiN2kN5BYtOm6pUfJG3Df0r_eCKDEofUlaLEYaAvnsEALw_wcB&ID=4283647184&cur_warehouse=CN

Maybe you can try dimming the laser electronically for example using pulse width modulation (PWM) signal to control the gate of a mosfet. Use that mosfet as the switch between battery and laser driver.

Thanks a lot eveyone. I ended up using just a polarizer and i can modulate the intensity by changing planar angle of polarizer to the incident light. It can reduce intensity upto 10%.

Amy Johnson

How about gray filters? They can be bought in various optical densities.

Pulsing the laser just reduces the average intensity. Is this sufficient? Just reducing the laser current would maybe bring the laser diode below the lasing threshold and then you could use an LED instead...

Hi Junaid,

happy to hear you found a decent solution to reduce your laser intensity by up to 10%.

I would suggest another cheap solution for reducing it further, simply by expanding the beam (using two lenses in a telescopic configuration) and by and additional iris to choose the desired portion of the expanded beam.

By adjusting the lenses ratio you can get increase your spot size and the beam intensity will in turn be reduced to your desired value.

Hope you will find this helpful.

Regards,

Nathaniel.

Nathaniel Hai I tried that but I do not have enough space between laser and the objective to place a lot of instruments. I have very special objective and if I place Iris close to the objective, I get whole IRIS imaged in the camera. Moreover, Expanding the beam and the using a converging lens is not going to allow me to change intensity dynamically. I would need to change the distance and both lens probably to achieve that and I am constantly switching between two different lasers. Polarizer works really good because it is just one plate and slight change in angle reduce intensity quite a lot. Nonetheless, I really appreciate your response. Thanks.

Marc Schneider I moved away from LED because I do not get good quality image. Laser I am using does not have current modulation so it only works at constant intensity. We have already burned one objective and that is why we are sticking to low power lasers but these ones have their own limitations and intensity control is one of them. I will look into grey filters. Thanks.

Amy Johnson

Neutral density filter is a simplesolution. If you want polarized beam and use a sheet polarizer then possibilty of leakage of orthoonal polarized beam arises.

It depends on laser initial intensity. All the above solutions work when demanded change of laser intensity is small. Absorbing filters are not the best solution for higher intensities since absorbed energy can change filter properties and result in beam deformation. Half reflecting mirror on transparent substrate is the best and when strong attenuation is necessary then total reflecting mirror will do the trick transmitting only fraction of initial laser density. Remember to incline slightly the mirror in order to avoid reflecting beam directly back into laser.

Amy Johnson

The best way is by external elements suitable for given laser intensity. Neutral density filters are OK for low power cw laser provided the beam is not focused. Even coloured glass may be sufficient.

Pulsed lasers even at low mean power may have high pulse intensity. Attenuation of high intensity beams is obtained by the use of beam splitters or attenuators working as semitransparent mirrors.

Junaid, simplest idea of reducing laser power below 10% is to use surface reflection over a glass plate. If the refractive index of the glass is 1.5 at the green laser wavelength, normal reflectance is given by ((1.5-1)/(1.5+1))^2=0.04. Shigeo

I think you can use Gray filters, also called as Neutral Density (ND) filters. These filters are available in different optical density i.e 0.3, 2, 3 etc. ND filter with 0.3 optical density transmits 50% output. You can use 1 or combination of these filters according to your measurement requirements.I would suggest that you mount these filters directly on to the objective lens then its convenient to use and change. For this, you will need an adapter that can fit objective lens internal threading and ND filter external threading.

What is power laser

Power laser means light amplification from stimulated emission of radiation .laser is created by specific process within the laser device to cause the controlled emission of radiation in form of radiation in form of light .lasers were first inverted in physiotherapists for relief of pain to accerelate healing and decrease inflammation.

Lower power laser is an output power of less than 0.5 walts is classified as low level laser therapy LLLT (class lll in the U.S.A),LLLT is often referred to as "cold laser''since they do not create a healing sensation during treatment.

Laser device is made up of an optical cavity or chamber that contains active medium for which laser is named .the chamber has mirrors either end that are perfectly parallel to each within a single wavelength of light .one of the mirror is paratially open .Electricity or energy is added to the medium which excites it .

ABSTRACT

Pain is the most common reason for physical consultation in the united states.one out of three Americans is affected by chronic pain annually.the number one reason for missed work or school days is musculoskeletal pain current accepted therapies consist of non steroidal anti inflammatory drugs steroid infectious ,opiate pain medications and surgery ,each of which carries their own specific risk profiles .what is needed at effective treatments of pain which have an acceptably low risk profile .for over forty years low level laser (light )therapy (LLLT) and LED(light emitting diode ) therapy (also known as photobiodilution) has been shown to reduce edema,induce analgesia and promote healing in a range of musculoskeletal pathologies .the purpose of this paper is to review the use of LLLT for pain,the biochemical mechanisms of action ,the dose response curves and how LLLT may be employee by orthopedic surgeons to improve outcomes and include adverse events.

KEYWORDS:-Musculoskeletal,pain,low level laser therapy ,photobiomodilution injury repair.

INTRODUCTION

Muscularskeletal pain affects 116 million Americans annually at a cost of $635 billion a year in medical bills lost productivity and missed work or school .All therapeutic treatments have processes different side effects risks and or complications the current treatment for muculoskeletal pain includes modalities ,immobilization,medications,chiroproactic care physical therapy behaviour management ,injection and/or surgery .these standard therapies have their associated risks /side effects profiles inckuding peptic ulcers (cardiovascular ),infections(including epidural access narcotic dependency/addiction ,deformities neurologic deficits and surgical complications ,the neutral history of chronic pain is one of increasing dysfunction impairment and possible disability .the definition of pain by the "lnternational association for the study of pain states ,pain unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage .clinically low level laser therapy (LLLLT)can treat noceptive and neuropathic pain,while central pain has not yet been proven to be responsive to LLLT .

WHAT IS LLLT(low level laser therapy).

Low level laser therapy (LLLT)sometimes known as low level light therapy or photobiomodilution(PBM) is also a low intensity light therapy .the effect is photochemical not thermal .the light triggers biochemical changes not thermal .the light triggers biochemical changes within cells and can be compared to the process of photosynthesis in plants,where the photons are absorbed by cellular photoreceptors and triggers chemical changes.

HISTORY OF LLLT

In 1903,Dr Nilas finsen was awarded a Nobel prize for his contribution to the treatment of diseases,especially lupus vulgaris ,with concentrated light radiation .ln 1960,professor maiman TH built the first working used ruby laser,but it was not until 1967 when mester E et al.was able to demonstrate the phenomenon of "laser bio stimulation "in 1999,where TT et al.presented his work on the medical applications of light emitting duodes (LED)for use on the NASA space station .

A laser is a device that generates light through a process of process of optical amplification based in the stimulation based in the stimulation emission of electromagnetic radiation

.there are four main classes of laser are defined by the international engineering consortrium (IEC standard 60825).these classes indicate potential danger the radiation is to edge.LLLT ES the application of light (usually a low power range of (10mw -500MW ).light with a wavelength in red of near infared region.

MECHANISMS OF LLLT

For low power visible or near infared light to have affect on a biologic system ,the photon must be absorbed by electrons absorption hands.belonging to a photon acceptor or chromosome(First law of photo biology).A chromophore is a molecule (or portion of a molecule )Which imparts a colour to a compound( e.g chlorophy 11 haemoglobin catochromes,flavin ,flavoproteins or porphyrins.the optical window in a tissue describes a range of wavelengths where the penetration of light into tissue is maximized by employing red and near infared wavelength has been estimated to be around 810 nm mitochondria are the cellular power points in our cells and such they convert food molecules and oxygen into energy (ATP)by oxiolation phosphorylstion.it has been proposed that cytochrome C oxidase is the primary photo acceptor for the red NR wavelength range in msmmalian cells.

Nitric oxide produced in mitochondria can inhibit respiratory by binding to cox and displace oxygen especially in injured or hypoxic cells.it is a proposed that LLLT can photo-dissociate no from cox and reverse the mitochodria in hibition of respiration due to excessive no binding .the process of light mediated vaso dialation was first RF survivor in 1968 and his research on biological properties of nitric oxide eventually led to the award of nobel prize in 1998.

LLLT is able to produce s shift in the overall cell redox potential in the overall cell redox potential in the direction of greater oxidation by increasing reactive oxygen species and decreasing reactive nitrogen species the long term effect of LLLT are thought to be due to the activation of various transcription factors by immediate chemical signaling molecules produce from mitochodria stimulation by LLLT .the most impottant of these signaling are thought to be ATR,cyclic Amp,no and rose.LLLT at low doses has been shown to enhence cell proliferation of fiblasts ,kerotinocytes endothelial cells and lymphocytes.

Amy Johnson

To everyone else, I have found a solution in form of polarizer as I stated before. I have already conducted my experiment and results look really good. Thanks for all of your comments.

Thanks for pointing it out.

The beam expander is a good solution if the beam shape is don't a matter